EASJ Notes

C# Programming
Exercises
(used in conjunction with Object-Oriented Programming With C#)

By Per Laursen
26-04-2017
Content
ProFun.0 ...................................................................................................................... 4
ProFun.1 ...................................................................................................................... 5
ProFun.2 ...................................................................................................................... 6
ProFun.3 ...................................................................................................................... 7
OOPFun.1..................................................................................................................... 8
OOPFun.2..................................................................................................................... 9
OOPFun.3................................................................................................................... 10
OOPFun.4................................................................................................................... 11
OOPFun.5................................................................................................................... 12
OOPFun.6................................................................................................................... 13
ProNex.1 .................................................................................................................... 14
ProNex.2 .................................................................................................................... 15
ProNex.3 .................................................................................................................... 16
ProNex.4 .................................................................................................................... 17
ProNex.5 .................................................................................................................... 18
ProNex.6 .................................................................................................................... 19
ProNex.7 .................................................................................................................... 20
ProNex.8 .................................................................................................................... 21
ProNex.8a .................................................................................................................. 22
ProNex.9 .................................................................................................................... 23
ProNex.10 .................................................................................................................. 24
ProNex.11 .................................................................................................................. 25
ProNex.12 .................................................................................................................. 26
DRY.1 ......................................................................................................................... 27
DRY.2 ......................................................................................................................... 28
OOPNex.1 .................................................................................................................. 29
OOPNex.2 .................................................................................................................. 30
OOPNex.3 .................................................................................................................. 31
OOPNex.4 .................................................................................................................. 32
OOPNex.5 .................................................................................................................. 33
OOPNex.6 .................................................................................................................. 34
DBI.0 .......................................................................................................................... 35
DBI.1 .......................................................................................................................... 36
DBI.2 .......................................................................................................................... 37
DBI.3 .......................................................................................................................... 38
DBI.4 .......................................................................................................................... 39
DBI.5 .......................................................................................................................... 40
DBI.6 .......................................................................................................................... 41
DBI.7 .......................................................................................................................... 42
DBI.8 .......................................................................................................................... 43
MVVM.0..................................................................................................................... 44
MVVM.1..................................................................................................................... 45
MVVM.2..................................................................................................................... 46
MVVM.3..................................................................................................................... 47
Files.1......................................................................................................................... 48
Excep.1 ...................................................................................................................... 49
MVVMStarter.1.......................................................................................................... 50
How to use this exercise set

This set of exercises is intended to be used in conjunction with the note Object-
Oriented Programming with C#. However, they are as such self-contained.

The formulation of each exercise follows a standard pattern:

 Exercise: Identifier for the exercise. The first part of the identifier is an
acronymed reference to the corresponding chapter in the notes.

 Project: A C# project used in the exercise. The specific details of how the
project is made available (.zip file, GitHub repository, etc.) may vary from
course to course. The projects are self-contained.

 Purpose: What aspect of the learning process does this exercise concern.

 Description: The “setup” for the exercise, typically some sort of simplified
domain-specific context.

 Steps: Specific steps in the exercise. The steps often become increasingly
difficult. Some steps are marked in red. These steps are considered quite
difficult.

To get around some technicalities with C# projects that are irrelevant for the begin-
ner, all projects contain an extra C# file called InsertCodeHere.cs. In that file, an area
is delimited by two comments

// The FIRST line of code should be BELOW this line

(sandbox area)

// The LAST line of code should be ABOVE this line

This area is referred to as the “sandbox area” in several exercises. If you are required
to put some code in the “sandbox area”, this is the place.
Exercise ProFun.0

Project Sandbox

Purpose Reality check – Visual Studio up and running

Description The Sandbox project is as simple as it gets – we will just use it to verify
that your installation of Visual Studio is up and running

Steps 1. Load, compile and run the project.

2. Verify that the message Hello world! Is printed on the screen.
Exercise ProFun.1

Project MovieManagerV05

Purpose Discuss variables with regards to types and naming

Description We imagine this project to be the very first steps in creating an appli-
cation for movie management. The application could be used to keep
track of relevant information for movies, e.g. a private collection of
movies on DVD/Blu-ray (yes, some people still watch movies on
physical media ).

Steps 1. Think about what specific information it could be relevant to

store for each movie.
2. For each specific piece of information, think about how you can
represent this information. Think about the nature of the infor-
mation; is it text, numeric, or something else.
3. In the sandbox area in the project, define a variable for each
piece of information. You should
a. Choose a proper type for the variable
b. Find a descriptive name for the variable
4. Once you are done, pair up with another student.
5. Switch computer with your partner
6. Review the work of your partner. For each variable in the
partner’s project, think about if
a. The purpose of the variable is easy to understand
b. The type seems properly chosen
7. Discuss your findings with your partner.
8. Was there any types of information that were particularly hard
to find a good representation for?
Exercise ProFun.2

Project WebShopV05

Purpose Get some practice in using arithmetic operators

Description Part of the business logic in a web shop involves calculating the total
cost of an order. The logic for calculating the total cost is as follows:
1. An item has a net price
2. You pay a 10 % tax on top of the net price
3. Shipping costs 49 kr., no matter the number of items
4. There is a credit card fee of 2 % on top of the entire cost,
including tax and shipping.

Steps 1. Load and open the project – you will see that some variables for
the net prices and number of items in order have already been
included. Also, the order details are printed on the screen.
2. The variable totalPrice is supposed to contain the total price for
the order. You must add the calculations needed to do this,
given the logic in the description.
3. Test your solution by varying the number of books, DVDs and
games in the order (you do this by assigning new values to the
noOf… variables)
4. The web shop decides to offer a discount, based on the total
number of items you buy:
 If you buy at least 15 items, you get a 5 % discount
 If you buy at least 30 items, you get a 10 % discount
The discount is applied to the total price – update the code to
include this discount.

Extra info Some test examples you can use to verify your solution:

Books DVDs Games Total price

8 3 2 711,96 kr.
0 12 4 1171,98 kr.
23 16 7 2507,16 kr.
Exercise ProFun.3

Project WebShopV06

Purpose Get some practice in using logical operators

Description Another part of the business logic in a web shop involves deciding if a
customer qualifies for certain special offers, based on the order. The
shop has four special offers. The logic for qualifying for each offer is:
1. The net total price (no taxes, etc.) is more than 1.000 kr.
2. You have ordered more books than games
3. You have ordered at least 10 items of one kind
4. You have ordered between 10 and 20 DVDs, or at least 5 games

Steps 1. Load and open the project – again, some variables are already
present. Note the boolean variables receiveSpecialOffer…
2. For each of these variables, you must specify a logical expres-
sion, corresponding to the logic given in the description.
3. Test your solution by varying the number of books, DVDs and
games in your order.
4. The web shop decides to offer an extra special offer. You qualify
for the extra offer, if you qualify for exactly two of the previous
offers. Update your code to include this extra offer.

Extra info Some test examples you can use to verify your solution (SO#1 means
“special offer 1”, and so on):

Books DVDs Games SO#1 SO#2 SO#3 SO#4

8 3 2 false true false false
0 12 4 false false true true
23 16 7 true true true true
3 5 4 false false false false
Exercise OOPFun.1

Project MovieManagerV10

Purpose Observe how to use an existing class.

Implement simple use of an existing class.

Description In this version of the movie manager, a class called Movie has been
added (in the file Movie.cs). It contains an absolute minimum of
information about a specific movie. The class is put to use in the
sandbox area, where some Movie objects are created and used.

Steps 1. Load the project, and go directly to the sandbox area. You will
see that some code is already present. See if you can figure out
what goes on in each line of code. If you hover the mouse
cursor over a specific element, you should see some useful
information pop up. Make sure you understand where
 Objects are created
 Parameters to the constructors are specified
 Properties are used
 Methods are called
 Return values are used
2. Feel free to create additional Movie objects, and exercise them
a bit (call methods, use properties, etc.)
Exercise OOPFun.2

Project BankV05

Purpose Implement minor additions to existing class.

Description The project contains a minimal BankAccount class. The class is put to
use in the sandbox area, where a BankAccount objects is created and
used.

Steps 1. Load the project, and take a look at the BankAccount class.
Make sure you understand the elements it contains. Then take
a look at how the class is used in the sandbox area.
2. We now want to add an extra property to the BankAccount
class: the name of the account holder. Add this feature to the
class. This will probably involve:
a. Adding an instance field
b. Adding a property
c. Updating the constructor
3. Once the class has been updated, make sure to test the new
feature by updating the code in the sandbox area.
Exercise OOPFun.3

Project RolePlayV10

Purpose Implement significant additions to an existing class.

Description The project contains a Warrior class, which is extremely simple – it

only contains a name property. We need to extend the class with a
few additional features.

Steps 1. Start out by taking a look at the Warrior class. Make sure you
understand the elements it contains. Then take a look at how
the class is used in the sandbox area.
2. We must now extend the class with a “level” feature. Details of
this feature are:
a. All warriors start at level 1.
b. The level can be retrieved freely, but not changed freely.
c. It must be possible to increase the level by one.
3. Implement this feature in the Warrior class. You will need to
consider if
a. An extra instance field is needed
b. An additional property is needed (if so, do we need both
the get and the set?)
c. The constructor needs to be updated.
d. A method for increasing the level is needed.
4. We must now extend the class with a “hit points” feature.
Details of this feature are:
a. Hit points are set individually when a warrior is created
b. Hit points can be retrieved freely, but not changed freely.
c. It must be possible to decrease hit points by a specified
amount.
5. Implement this feature in the Warrior class, going through the
same considerations as for the level feature
6. Implement a property called Dead, which returns a boolean
value. The property should return true if hit points are below
zero.
Exercise OOPFun.4

Project ClockV10

Purpose Implement a class from scratch, including use of the class

Description This project contains an empty class definition Clock. Your job is to
implement the class, given the below requirements:
1. The clock should keep track of hours and minutes.
2. The clock should use the 24-hour system.
3. It must be possible to set the clock to a specific time.
4. It must be possible to retrieve the current time from the clock.
5. It must be possible to advance the clock by a single minute.

Steps 1. Implement requirements 1-4. This will involve figuring out what
instance fields, constructor, properties and methods you need
for this. Remember to include code for testing the class.
2. Implement requirement 5. In this case, it becomes quite
important to choose relevant test cases.
Exercise OOPFun.5

Project DiceGame

Purpose Work with a project containing collaborating classes

Description This project contains two classes: Die and DiceCup. The Die class
represents a 6-sided die, and is completed. The DiceCup class needs a
bit of work to be complete. The DiceCup class uses the Die class.

Steps 1. Take a look at the Die class. It is complete, and fairly simple.
Note that we use another class in the Die class, called Random.
This class is from the .NET class library.
2. Open the DiceCup class. Note how the class contains two
instance fields of type Die. Also note the constructor – what
happens there?
3. The DiceCup class is not complete. Implement the Shake
method and the TotalValue property, as specified in the
comments in the code. Test that your code works as expected,
by creating and using a DiceCup object in the sandbox area.
4. How much would we need to change in order to have a dice
cup with three dice?
5. When we create a DiceCup object, we would also like to be able
to specify the number of sides the dice should have. Implement
the necessary changes in Die and DiceCup needed to enable
this feature.
Exercise OOPFun.6

Project StaticExamples

Purpose Defining and using static classes, methods and instance variables.

Description The project contains the class ListMethods, which defines two
methods FindSmallestNumber and FindAverage. The names should
hopefully indicate what they do. Code that tests the class is included
in the sandbox area. The class is tested in the traditional way; create
an object, and call methods on the object.

Steps 1. Change the ListMethods class into a static class. Remember

that a static class can only contain static methods.
2. Modify the code in the sandbox area , such that it uses the
ListMethods class as a static class. The output of running the
application should of course be as before.
3. The project also contains a simple class Car (see the code). We
would now like to track how the class is used. More specifically,
we wish to track the number of
a. Car objects that have been created
b. Uses of the property LicensePlate
c. Uses of the property Price
4. Add static instance fields to the Car class, to enable the tracking
described above. Increment the value of each variable at the
appropriate place in the class.
5. Add a static method that can print out the values of the static
instance fields. It could be called PrintUsageStatistics.
6. Test that your additions work, by including some test code in
the sandbox area. Create and use some Car objects, and finally
call the static method to observe the usage statistics.
Exercise ProNex.1

Project BankV10

Purpose Use simple if-statements in an existing class.

Description This project contains a minimal BankAccount class, that sort of works.
However, it has some problems…

Steps 1. Test the BankAccount class, by adding code in the sandbox

area. Specifically, make some tests that make the balance go
negative.
2. Now change the code in the Withdraw method, such that a
withdrawal is only done if the balance is larger than or equal to
the given amount. Remember to test that the change works as
expected.
3. This makes the BankAccount class more realistic, but there are
still problems – you can call both Withdraw and Deposit with
negative amounts (try it), which does not make much sense.
Make changes to both methods, such that they only perform a
withdrawal/deposit if the given amount is positive. Remember
that for the Withdraw method, the change made in part 2 must
still work!
4. Test that all your changes work as expected.
5. If we call Withdraw or Deposit, and detect an error situation,
we don’t do anything… What should we do?
Exercise ProNex.2

Project WTF

Purpose Use if-else-statements. Use method calls creatively.

Description This project contains a class called MysticNumbers, with a single

method ThreeNumbers. All that is known about ThreeNumbers is
that it takes three integers as input, and returns one of them

Steps 1. By reading the code for ThreeNumbers, try to figure out what it
does. Write some test code to see if you are right.
2. Write and test a new method TwoNumbers, that does the same
thing as ThreeNumbers, but now only for two numbers.
3. Write and test a new method FourNumbers, that does the
same thing as ThreeNumbers, but now for four numbers (tip –
you can probably use the method TwoNumbers to make the
code fairly short and easy).
4. Rewrite ThreeNumbers to use the TwoNumbers method. What
code do you like best – the original code or the new code?
Exercise ProNex.3

Project WeatherStationV10

Purpose Use multi-if-else-statements.

Description This project contains a class called Barometer, containing two

properties Pressure and WeatherDescription. The latter property
gives an old-fashioned description of the weather, as a function of the
pressure, according to this table:

Pressure WeatherDescription
Below 980 Stormy
980-1000 Rainy
1000-1020 Changing
1020-1040 Fair
Above 1040 Very dry

Steps 1. Implement the property WeatherDescription, according to the

table in the description.
2. Test your code.
Exercise ProNex.4

Project WhileLoopsBaseCamp

Purpose Get some experience with while-loops

Description The project contains some counter-controlled while-loops, and some

number sequences that should be generated using while-loops.

Steps 1. In the sandbox area, four while-loops (Case 1-4) are given. Try
to figure out what the output from each loop will be. When
ready, uncomment the line in each loop that prints the current
value of the counter variable, and see if you were right.
2. Next follows Case 5-8. Here you must implement a while-loop
yourself, to produce the number sequence given in the
comment for each case.
Exercise ProNex.5

Project CorrectChangeAutomat

Purpose Use while-loops for a more complicated problem

Description This exercise is about calculating the correct change when a customer
pays a due amount with too much cash (yes, some people still pay
with cash…).
Example: A customer has to pay 266 kr., but pays 500 kr.. The custo-
mer must then receive 234 kr. in change. The tricky part is to figure
out how to pay this amount using ordinary bills and coins, and paying
back as few bills and coins as possible. In this example, the correct
way to pay back correct change would be:
 One 200-kr bill
 One 20-kr coin
 One 10-kr coin
 Two 2-kr coins

Steps 1. Implement code to calculate and print out the correct change.
To keeps things simple, we assume that you only use 100-kr
bills, 10-kr coins and 1-kr coins. Remember to test your code
with some different values for change. You can just add the
code in the sandbox area.
2. Once the above problem is solved, include some more bills and
coins, like 50-kr bills, 5-kr coins, etc..
3. If you used while-loops for solving the problem: Try to solve the
problem without using loops.
Exercise ProNex.6

Project RolePlayV20

Purpose Get further experience with while-loops. Work with a project

involving several classes.

Description The project is supposed to model a very simple game, where a hero
can battle against a beast, until either beast or hero is dead! The
project contains four classes, which are described in general terms
here – see the code for more details:
 The NumberGenerator class, with the method Next. This is a
helper class for generating random numbers.
 The BattleLog class, where individual strings can be “saved”,
and later on printed out on the screen.
 The Hero class, which models a game character. It is a very
simple model, since it just has a number of hit points.
 The Beast class, which also models a game character, in a way
similar to the Hero class.
Even though this is a very simple setup, it does include fundamental
game mechanics from many popular role-playing games.

Steps 1. Study the classes in details, so you are sure of what they can do
and how they work. Note how the Hero and Beast classes make
use of the NumberGenerator and BattleLog classes.
2. See if you can figure out how to code a battle between a Hero
and a Beast (until the death!). A bit of code is present in the
sandbox area, but it obviously needs to be extended.
3. When you can make the two objects battle each other, there
are a number of things to consider afterwards:
a. It seems like the Hero wins most of the time (depending of
course on how you coded the battle…). Why is that? How
could we make the battle more fair?
b.The damage dealt by the Hero is always between 10 to 30
points. How could we change that? Could we even let the
creator of the Hero object decide this interval? Could this
also be done for the number of initial hit points?
c. Do we really need separate classes for Hero and Beast?
Exercise ProNex.7

Project DrawShapes

Purpose Get some experience with for-loops

Description This exercise is about trying to draw some simple shapes on the
screen, using for-loops to get the job done. A very simple class
DrawingTool is provided to help with this.

Steps 1. Study the class DrawingTool. As you can see, it is very simple.
Why is the class (and the methods) static?
2. Using for-loops and the DrawingTool class, see if you can create
code to draw the shapes A to E, as defined in the comments in
the sandbox area. NOTE: The shapes get increasingly hard to
draw…
Exercise ProNex.8

Project ListBaseCamp

Purpose Get some experience with methods in the List class.

Description This exercise is about predicting the result of applying some methods
of the List class to a List object, and also about writing some code to
use a List object

Steps 1. In the sandbox area, a List object is created, and some elements
are added and removed. At four points in the code (Case 1-4),
you must predict the outcome of the WriteLine statement.
When ready, you can uncomment the WriteLine statement,
and see if your prediction was correct.
2. Following the cases above, four more cases are given (Case 5-
8), where you must write code that use the List object, to
retrieve various information about the elements in the list.
Details for each case are given as comments in the code.
Exercise ProNex.8a

Project RolePlayV21

Purpose Get some experience with the List class.

Description This exercise picks up where ProNex.6 let off. Now the Hero must face
a greater challenge! (or maybe he’s just farming..).

The project RolePlayV21 is identical to the solution to ProNex.6. The

Hero can do a battle against a Beast, and both classes now take
several parameters in their constructor.

Steps 1. Change the code in InsertCodeHere.cs, to do a battle between a

single Hero and an army of Beasts. (Hint: You will need a List
and a couple of repetition statements). You might need to
adjust the strength of Beasts, to give the Hero a chance…
Exercise ProNex.9

Project LibraryV10

Purpose Use the List class. Implement linear search.

Description This exercise illustrates the concept of a catalog. A catalog is a class

that can store and use data of a certain type, without revealing the
specific representation of data to the user of the catalog.

The project contains the simple domain class Book (we consider the
isbn number to be a “key” for Book, i.e. no two Book objects can have
the same isbn number). Also, it contains the (incomplete) catalog class
BookCatalog. The three public methods in BookCatalog allow the user
to store and use Book objects in a simple way (see the comments in
the code for more details about each method).

Steps 1. Study the test written in the sandbox area, and figure out what
you expect the test to output.
2. Complete the three methods in the BookCatalog class.
3. Run the application, and see if the output of the test matches
your expectations (if not, you will have to examine the test and
your code once again…).
4. Is there anything in the code that prevents a user from adding
two Book objects with the same isbn value?
5. How could you prevent that Book objects with the same isbn
value are added to the catalog?
Exercise ProNex.10

Project LibraryV11

Purpose Use the Dictionary class.

Description NOTE: This exercise is intentionally almost identical to ProNex.9

This exercise illustrates the concept of a catalog. A catalog is a class

that can store and use data of a certain type, without revealing the
specific representation of data to the user of the catalog.

The project contains the simple domain class Book (we consider the
isbn number to be a “key” for Book, i.e. no two Book objects can have
the same isbn number). Also, it contains the (incomplete) catalog class
BookCatalog. The three public methods in BookCatalog allow the user
to store and use Book objects in a simple way (see the comments in
the code for more details about each method).

Steps 1. Study the test written in the sandbox area, and figure out what
you expect the test to output.
2. Complete the three methods in the BookCatalog class.
3. Run the application, and see if the output of the test matches
your expectations (if not, you will have to examine the test and
your code once again…).
4. Is there anything in the code that prevents a user from adding
two Book objects with the same isbn value?
5. How could you prevent that Book objects with the same isbn
value are added to the catalog?
Exercise ProNex.11

Project SchoolAdministrationV10

Purpose Use the Dictionary class. Work with an application containing several
classes.

Description The project contains the class Student. This is a simple representation
of a student, with three instance fields; id, name and test scores. The
first two are simple, but the “test scores” field is a Dictionary, holding
key-value pairs of course names (string) and scores (int).
The project also contains the class StudentCatalog. This class is sup-
posed to be able to retrieve various information about the students;
for this purpose, an instance field _students of type Dictionary is used
to hold key-value pairs consisting of ids and Student objects (since a
student is uniquely identified by an id)

Steps 1. The class Student is complete, and you need not change
anything in it. However, take a good look at the Student class
anyway, and make sure you understand how the methods
work. Pay particular attention to the property ScoreAverage.
2. Look in the class definition of StudentCatalog. It contains five
properties/methods (Count, AddStudent, GetStudent,
GetAverageForStudent, GetTotalAverage) that are not
completed. Add code to complete these methods, according to
the specification given in the comments in the code.
3. Code that tests the StudentCatalog class has been added in the
sandbox area,. Run the application, and check that the Student-
Catalog class behaves as expected.
Exercise ProNex.12

Project Flinter

Purpose Use enumerations

Description Flinter is supposed to be the start of a new dating app. You can create
profiles for those you are interested in meeting.

In the project, the class Profile has been included. The class contains
instance fields for gender, eye color, hair color, and height. You can
thus create a Profile object by specifying values for each of these four
fields in the class constructor. Furthermore, you can get a text
description of a Profile object by using the property GetDescription.

Steps 1. Code that tests the Profile class is as always included in sandbox
area. Examine the code in the Profile class definition, and see if
you can predict the outcome of running the test.
2. Running the test reveals some problems. In two cases, we have
specified hair color where we should have specified eye color,
and vice versa (unless you really want a partner with white eyes
and blue hair…), and in one case, we have specified a height
category that doesn’t exist. Change the Profile class definition
by adding enumerated types for gender, eye color, hair color
and height category. Use these new types for the four instance
variables. The constructor needs some changes as well. Also
consider if you still need the properties GenderDescription and
HeightDescription.
3. Change the code in the sandbox area , so it is compatible with
the redesigned Profile class. Observe how it is now only
possible to specify legal values for each type.
4. Reflect a bit on the changes. Is there anything in the new code
that is more complicated than it was in the original code? Was
it always relevant to use an enumerated type?
Exercise DRY.1

Project CalculationSimulation

Purpose Improve code structure by replacing values with constants, instance

fields and parameters

Description The project contains a simple simulation of a calculation. The inten-

tion is to simulate a calculation that takes about half a second. The
calculation takes two values x and y, and returns an integer value.

In order to speed up the calculation, a “cache” class is also provided.

The idea is that once a calculation has been done, the result can be
stored in the cache, from which it can be retrieved very quickly. See
the code for further details.

Steps 1. The code is set up to do calculations in a 5x5 table (that is, x and
y can be numbers between 0 and 4, both included). How many
places in the project would you have to change something, if
you want to do calculations in a 10x10 table instead?
2. Change the code, such that you get rid of all the instances of
the number 5 in the methods. This could be done by using
constants, instance fields and parameters.
3. It seems like -1 means “no value”. Change the code, such that
the value -1 does not occur in the methods.
4. Are there other values that are candidates for being replaced
with constants or parameters? If so, make the necessary
updates to the code.
Exercise DRY.2

Project WebShopV10

Purpose Improve code structure by creating new methods

Description Part of the business logic in a web shop involves calculating the total
cost of an order. The logic for calculating the total cost is found in the
code in the project.
In the project, the Order class contains an item list. For simplicity, the
item list just contains the net price for each item in the order. The
class also contains a property TotalOrderPrice for calculating the total
price for the order.

Steps 1. The implementation of the TotalOrderPrice property is less

than optimal. Rewrite it, with the intent of:
a. Removing duplicate code
b. Making the method easier to understand
Exercise OOPNex.1

Project EmployeeV10

Purpose See inheritance in action. Reorganise existing code to use inheritance.

Call base class constructors.

Description The project contains two existing classes Teacher and ITSupporter.
They have quite a lot in common, so there is a lot of code duplication
to get rid of.

Steps Reorganise the code using inheritance

1. Create a new class Employee, that contains the common parts

from Teacher and ITSupporter.
2. Let Teacher and ITSupporter inherit from Employee. The code
in InsertCodeHere.cs should work as before. Remember that
the derived classes will need to call the base class constructor.
Exercise OOPNex.2

Project RolePlayV23

Purpose Override existing methods in derived class

Description The project contains a working role-play system. Any character in the
game is represented by an object of the class Character.

Steps 1. Get an overview of the application. The most interesting class is

the Character class, which implements a generic game charac-
ter. Also note the code in InsertCodeHere.cs, where two teams
with two members are set up for battle.
2. Create a class Defender, which derives from Character. A
Defender has a 50 % chance of having the received damage
reduced by 40 %. This means that the ReceiveDamage method
must be overrided. Once you have created the class, update the
code in InsertCodeHere.cs to include a Defender on each team.
3. Create a class Damager, which derives from Character. A
Damager has a 40 % chance of dealing double damage. This
means that the DealDamage method must be overrided. Once
you have created the class, update the code in InsertCode-
Here.cs to include a Damager on each team.
4. Can we organise the code better, in order to e.g. make calls to
the base class methods for dealing and receiving damage?
(Maybe the calculation and the logging should be separated
into separate methods).
Exercise OOPNex.3

Project SimpleGeometry

Purpose Override abstract methods. See polymorphic behavior in action.

Description The project contains the (abstract) class Shape, with an abstract
property Area. The class also contains a static method FindTotalArea,
that should calculate the total area of a list of shapes

Steps 1. Create two classes Circle and Rectangle. Both classes should
inherit from Shape, and therefore implement the abstract
property Area. You also need to figure out what instance fields,
etc. the two classes need (if you need the value of π (pi), you
can get it by writing Math.PI).
2. Implement the FindTotalArea method properly, such that it
finds the total area of a list of shapes.
3. In the sandbox area, fill in some shapes in the given list, and see
if your implementation works as expected
Exercise OOPNex.4

Project FilteringV10

Purpose Use interfaces to generalise code

Description The project contains a class Filter, with a FilterValues method. The
method filters out values higher than 10 from a list of integers. The
project also contains an interface IFilterCondition.

Steps 1. Figure out how you can use the interface IFilterCondition to
change the FilterValues method, into a method that can filter a
list of integers according to any condition. That is, the condition
itself has to somehow become a parameter to the method. Try
out your solution with a couple of conditions.
2. Figure out how you can apply several filter conditions to a list in
a single method call.
3. Filtering is a very generic operation. Maybe some of the .NET
collection classes already support filtering…?
Exercise OOPNex.5

Project CarDealershipV05

Purpose Override methods from Object class.

Description The project contains a simple class Car, which contains a few proper-
ties. In the sandbox area, we attempt to print out Car objects, and
perform some comparisons between Car objects.

Steps 1. Run the program as-is, and observe the result. Can you figure
out when the comparisons return true?
2. In the Car class, uncomment the Equals method (only that
method), and run the program again. What has changed?
3. Uncomment the rest of the code in the Car class, and run the
program again. What has changed?
4. The printing of Car objects is still not very satisfying. In the Car
class, override the ToString method, so that it returns a string
giving a reasonable description of the Car object. Run the
program again, and see what difference it makes.
Exercise OOPNex.6

Project CompanyV10

Purpose Use inheritance when creating several classes

Description The project contains very little from the start. There is an Employee
class with a Name property, and some abstract properties. Concerning
salary calculation, only some very general rules exist:
 Part of the salary is a fixed amount
 Part of the salary is a bonus amount
 The bonus amount is paid if a certain condition is met
Specific definitions of the rules should be defined in classes that
inherit from Employee

Steps 1. Create a Worker class. The class should inherit from Employee.
For a worker, the below rules apply:
 A worker works a fixed amount of hours per month
 A worker is paid a fixed amount per hour
 A worker does not receive any sort of bonus

2. Create a Manager class, also inheriting from Employee. The

rules for salary calculation are more vague for a manager:
 A manager has a fixed monthly base salary
 A manager has a fixed monthly bonus
The condition for when the bonus is paid out may vary,
depending on the specific type of manager (NB: This implies
that Manager also becomes an abstract class).

3. Create a JuniorManager class, that inherits from Manager. A

junior manager will have the bonus paid out if (s)he has worked
at least 180 hours during the month.

4. Create a SeniorManager class, that inherits from Manager. A

senior manager will have the bonus paid out if (s)he has a
performance evaluation of at least 6 during the month
Exercise DBI.0

Project ExamAdmV10

Purpose Create data bindings between GUI controls

Description The project contains a simple GUI for an exam administration system.
In this version, you can just type in a name, a subject and a test score
for an exam. The data is entered through two text boxes and a slider
control.

Steps 1. Open the project, and open the MainPage.xaml file. Even
though the file contains quite a bit of XAML, we only need to
focus on the three named controls, with the names student-
Name, subject and score (two TextBox controls and a Slider
control). Make sure you can find these three controls in the
XAML code.
2. We want to bind three TextBlock controls to the value of the
three named controls. The three TextBlock controls are all part
of the top line of the GUI, which consists of a total of six
TextBlock controls. For each of the three relevant TextBlock
controls, figure out which specific named control to bind to.
3. Now create the actual bindings, using the syntax described in
the notes (for a Slider, you bind to the Value property; for a
TextBox, you bind to the Text property).
4. Test that your bindings work as expected
Exercise DBI.1

Project ExamAdmV11

Purpose Create data bindings between GUI controls and a domain object

Description The project is identical to the project from ExamAdmV10, except that
a class Student has been added. Right now, the constructor in Student
just sets the properties to some fixed values.

Steps 1. Open the MainPage.xaml file, and add a data context to the
Page control, specifying Student as the data context. See the
notes for the syntax for adding a data context.
2. Bind the three relevant TextBlock controls (the same as in the
previous exercise) to the corresponding properties on the
Student class. Again, see the notes if you cannot remember the
syntax for this.
3. Also create bindings for the three named controls, such that
each control – or more precisely; the relevant property in each
control – is bound to the corresponding Student property.
4. Run the application, and check that the bindings work as
expected. Try to change the values as well. Are the changes
reflected in the text line at the top?
Exercise DBI.2

Project ExamAdmV12

Purpose Create two-way data bindings between GUI controls and a domain
object

Description The project starts off where the previous exercise left off. The project
does contain data bindings, but changes in the values are still not
reflected in the rest of the GUI.

Steps 1. Open and run the application. Confirm that changes in the
values are not reflected in the top text line.
2. Open the Student class. All three properties now have a set-
part as well. Now let Student inherit from the INotifyProperty-
Changed interface, and implement the OnPropertyChanged
method (if ReSharper if installed, Visual Studio can generate the
code for you. If not, you can simply copy-paste the code from
the notes).
3. Run the application again – are value changes now reflected in
the text line?
4. For each property in Student, add a call to OnPropertyChanged
to the set-part of the property, after the value has been set.
5. Run the application again – are value changes now reflected in
the text line?
6. For each of the three bindings for the named controls (not the
TextBlock control), update the binding mode to TwoWay.
7. Run the application again – are value changes now reflected in
the text line?
8. Why don’t we need to update the three TextBlock bindings to
being TwoWay?
Exercise DBI.3

Project ExamAdmV13

Purpose Create data bindings between collection-oriented GUI controls and

domain object collections

Description We now introduce a StudentCollection into the application. For now,

it contains a Student list (with one entry), and a subjects list (initia-
lised with five entries). The class also has a property SelectedStudent,
that for now just returns the single entry in the Student list.

Steps 1. Open the StudentCollection class, and make sure you under-
stand the instance fields and properties it contains (except the
NewSubject property)
2. Open the MainPage.xaml file. The bindings are now a bit more
complex, since the data context is now StudentCollection. Most
properties are now bound to the corresponding property on the
SelectedStudent property (i.e. Student object). Make sure you
understand the new bindings.
3. Run the application (ignoring the two extra lines beneath
“Score”). The application does work, since updates to name,
score and subject are reflected in the top text line (try it!).
4. In the “New subject” line, the intention is that when a new
subject is entered, it should show up in the Subject combo-box.
Confirm that this is not the case right now (remember that you
must leave the text box, before the update is triggered).
5. The “No. of subjects” field tells how many entries the _subjects
list in StudentCollection contains. Right now, the number stays
at 5. Figure out how to create a binding for the text box next to
the “New subject” text, such that a new entry is indeed added
to _subjects (Hint: Take a look at the NewSubject property in
StudentCollection).
6. Once this binding works, the number should increase every
time a new subject is added. Still, the new subjects do not show
up in the combo-box. Figure out why this is the case, and fix it.
(Hint: Are we using the correct collection class for _subjects?)
Exercise DBI.4

Project ExamAdmV14

Purpose Create a data template for presenting objects in a ListView

Description The application main view contains a ListView control, where the
ItemsSource property is bound to the Students property on the
StudentCollection class. The list contains five students. However, the
presentation of the students in the list view is not optimal.

Steps 1. Try to improve the presentation of Student objects in the list

view, by providing an implementation of ToString in the
Student class.
2. Improve the presentation further by defining a data template
for the Student class (Tip: you can probably use the properties
in the Student class for this purpose).
Exercise DBI.5

Project ExamAdmV15

Purpose Create a Master/Details view

Description The application main view again contains a ListView control, where
the ItemsSource property is bound to the Students property on the
StudentCollection class. The list contains five students, and a reason-
able data template has been provided for presentation. The Student
class has however been extended with several additional properties.

Steps 1. Create the Details part of a Master/Details view (the ListView is

the Master part), such that all details of a given Student object
are shown in the Details part. The Details part should show the
details of the Student which is currently selected in the list
view. (Tip: use the example in the notes for inspiration).
2. Use the styles TextBlockStyle and TextBoxStyle to specify the
appearance of the Details part.
Exercise DBI.6

Project ExamAdmV16

Purpose Add deletion functionality to a Master/Details view

Description The application contains a working Master/Details view for the

Student class. We now wish to add functionality to delete a student

Steps The steps needed to create deletion functionality are very similar to
the steps described in the notes. Almost all changes are done in the
StudentCollection class. It can be assumed that the Name property
can be used as a key for Student objects.

In the StudentCollection class:

1. Change the _students instance field, such that it uses Obser-
vableCollection instead of List
2. Add a DoDelete method, similar to the DoDelete method in the
notes (it should call the existing Delete method)
3. Add a DoDeleteRelay method, similar to the DoDeleteRelay
method in the notes
4. Add a StudentIsSelected method, similar to the CarIsSelected
method in the notes
5. Add a _deleteCommand instance field, of type RelayCommand
6. Initialise the _deleteCommand instance field in the constructor,
using DoDeleteRelay and StudentIsSelected as parameters
7. Add a DeletionCommand property, similar to the Deletion-
Command property in the notes
8. Update the set part of the SelectedStudent property, such that
it calls _deleteCommand.RaiseCanExecuteChanged()

In the MainPage.xaml file:

9. Add a Delete button in a proper place in the view, and bind its
Command property to DeletionCommand

10.Check that you can now delete students from the view!
Exercise DBI.7

Project ExamAdmV17

Purpose Consider how insertion/editing functionality can be added to the

application

Description The application contains a working Master/Details view for the

Student class, with deletion functionality. A natural extension of the
application could be to add functionality for editing existing students,
and adding new students

Steps 1. Consider what it would take in order to add insertion and

editing functionality to the view. Consider for instance:
 How can we enable editing of specific fields?
 Should all fields be editable?
 Should editable fields be editable all the time?
 How can we manage the “editability” of fields in the
Details view?
 What are the detailed steps needed in order to create a
new student?
 What sort of validation will be needed when creating a
new student (remember we assume that student names
are unique)?
2. If you are up to the challenge, feel free to start on the actual
implementation of the functionality
3. Finally, consider if the Student and StudentCollection classes
are appropriate classes for containing all this functionality. Can
you envision a better distribution of the functionality?
Exercise DBI.8

Project ExamAdmV18

Purpose Save the day at StudentSoft A/S (see memo below)

Description MEMO: Finish the Show/Hide details feature in the Student view
From: Maurice Fischer (StudentSoft A/S CTO)
TO: EASJ Intern (can’t remember the name…)

Hi,
Unfortunately, our main developer on the Exam Administration
application died yesterday, due to an unfortunate incident involving a
hamster, three small oranges and a large piece of brown cardboard.
We would therefore like you to finish up the Show/Hide Details
feature he was working on in the Students view. I think it was
something about being able to toggle the visibility of parts of the
Details view on and off, using a ToggleSwitch or something… Anyway,
you can probably figure it out by looking in the C# project, as he said
he was “almost done” with it, and he always puts…uhh, used to put
comments in the code. I would like a demo of it later today, as we are
shipping a new version of the application tomorrow.

Regards,

M. Fischer

Steps Do as you’re told…

Exercise MVVM.0

Project ExamAdmV20

Purpose Change the given application from a Model-View (MV) architecture to

a Model-View-ViewModel (MVVM) architecture.

Description The project initially contains a class Student, which acts both as a
domain class and a “provider” to the main view (via data bindings in
MainPage.xaml).

Steps Add a new class StudentViewModel to the project, which will acts a the
ViewModel in an MVVM architecture. This involves:
1. Create the class StudentViewModel.
2. Add an instance field _domainObject of type Student to StudentView-
Model, and initialise it to refer to a new Student object in the constructor.
3. Let StudentViewModel inherit from INotifyPropertyChanged, and
generate the code needed (Tip: click the lightbulb ). If the includes are
not generated automatically, add to the top of the file:
using System.ComponentModel;
using System.Runtime.CompilerServices;
4. Add properties Name, Subject and Score to StudentViewModel, in the
style described in the notes.
5. Clean up the Student class, such that it no longer inherits from
INotifyPropertyChanged
6. Change the data context in MainPage.xaml, and check that the new
bindings work as expected.
7. Now create a new property TopLineText in StudentViewModel, of type
string. The intention is that this property should provide enough
information to enable you to delete the six TextBlocks in the top line of
the GUI, and replace them with a single TextBlock, that binds to
TopLineText.
8. Delete the six TextBlocks, replace them with a single TextBlock, and bind
the new TextBlock to TopLineText. Are changes to the data reflected in
the top text line?
9. Add extra calls of OnPropertyChanged to the Name, Subject and Score
properties, in the style described in the notes. Check that changes are now
reflected in the top text line
Exercise MVVM.1

Project ExamAdmV21

Purpose Add and use view model classes in an application

Description The given application provides simple read-only functionality for a

collection of students (only the Master part of a Master/Details view).
For now, the class StudentItemViewModel is not used.

Steps 1. Add a new class StudentMasterViewModel to the project. The intention is

that MainPage.xaml should use this class as its new data context.
2. Add two instance fields to the new class:
 _studentCollection of type StudentCollection
 _studentItemViewModelCollection of type
ObservableCollection<StudentItemViewModel>
3. Initialise the two instance fields in the constructor, by setting them to
refer to a new object of each type.
4. Still in the constructor, add StudentItemViewModel objects to
_studentItemViewModelCollection, by looping through the list of Student
objects in the collection (Hint: use the Students property in the
StudentCollection class), and create a new StudentItemViewModel object
for each Student object.
5. Add a property StudentItemViewModelCollection to StudentMaster-
ViewModel. Only the get-part of the property is needed; it should just
return _studentItemViewModelCollection.
6. Change the data context in MainPage.xaml to use StudentMaster-
ViewModel instead of StudentCollection, and change the binding of the
ListView property ItemsSource from Students to
StudentItemViewModelCollection.
7. Rebuild the application, and check that the data is still shown properly
when running the application.
8. Do these changes enable you to clean out any properties from Student
and StudentCollection, that were only there to supply GUI-specific data?
Exercise MVVM.2

Project ExamAdmV22

Purpose Add deletion functionality to a working read-only Master view.

Description The application contains a functional read-only Master view, where

students can be viewed. The application uses the MVVM architecture.
We now want to add deletion functionality to the application

Steps In the StudentMasterDetailsViewModel class:

1. Add a new property DeletionCommand (only the get-part is needed) of
type ICommand, that returns _deleteCommand.
2. Implement a CanDelete method, that returns a bool. The method should
return true when it is meaningful to execute the deletion functionality
(Hint: A student should probably be selected in the view).
3. Implement a DoDelete method, that deletes the selected student, using
the name of the student as key (Hint: Use the already implemented Delete
method ).
4. With CanDelete and DoDelete implemented, now make a proper
initialisation of the _deleteCommand instance field (Hint: Use the
RelayCommand class, using DoDelete and CanDelete as parameters).

In MainPage.xaml
5. Add a Delete button just after the ListView control, and bind its Command
property to DeletionCommand
6. Build and run the application. Does the Delete button work as it should
(probably not…)

Back in the StudentMasterDetailsViewModel class:

7. In the set-part of the StudentItemViewModelSelected property, add a call
of RaiseCanExecuteChanged on the _deleteCommand instance field, just
before the call of OnPropertyChanged.
8. Build and run the application again. Does the Delete button now work as it
should (Hopefully it does )
Exercise MVVM.3

Project ExamAdmV23

Purpose Rewrite domain-specific classes to use provided base classes

Description The project contains a working Master view with delete functionality.
All domain-specific classes are located in the folder DomainClasses.
A number of base classes are available in the folder BaseClasses, but
are not used yet.

Steps 1. Let the Student class inherit from DomainClassBase<string>. This will
require that you override the get-part of the property Key. The property
should just return _name (name acts as key for a Student object).
2. Let the StudentModel class inherit from ModelBase<Student, string>. You
can then delete everything else from the StudentModel class except the
constructor. In the constructor, change the calls of _students.Add to use
the base class method Add.
3. Let the StudentItemViewModel class inherit from ItemViewModel-
Base<Student>. The constructor must then call the base class constructor
with obj as parameter. Also delete the instance field _domainObject, and
replace the use of _domainObject with DomainObject in the properties.
4. Let the StudentMasterViewModel class inherit from MasterViewModel-
Base<Student, string>. You can then delete the method GetStudentItem-
ViewModelCollection from the class.
5. Open the StudentViewModelFactory.cs file, and uncomment the class
StudentViewModelFactory. (tip: select all of the code, and press Ctrl+K+U)
6. Let the StudentMasterDetailsViewModel class inherit from
MasterDetailsViewModelBase<Student, string>. Then delete everything
(yes, everything) from the class…
7. Implement the constructor for StudentMasterDetailsViewModel like this:
public StudentMasterDetailsViewModel()
: base(new StudentViewModelFactory(), new StudentModel())
{}
8. In MainPage.xaml, change the binding of ItemsSource to ItemView-
ModelCollection, and the binding of SelectedItem to ItemViewModel-
Selected
9. Make sure all files are saved, then build and run the application
Exercise Files.1

Project NoteBookV10

Purpose Add Load- and Save-functionality to an MVVM application

Description The given application contains a very simple system for creating
notes. A note consists of a title and some content. It is not allowed to
have two notes with the same title. However, the application does not
support saving and loading of notes yet.

Steps In the NoteMasterDetailsViewModel class:

1. Add a new instance field _loadCommand, of type RelayCommand
2. Add a new property LoadCommand, of type ICommand. It should just
return the instance field _loadCommand, in the same style as e.g. the
AddCommand property.
3. Add a new method Load, in the same style as in the notes. That is, it
should call Load on the _model instance field.
4. In the constructor, initialise _loadCommand in the same style as in the
notes.
5. In the method NotifyCommands, add a call of RaiseCanExecuteChanged
on the _loadCommand instance field
6. Repeat steps 1-5 for the Save functionality

In the MainPage.xaml file:

7. Add two new buttons Load and Save to the view, and bind them to the
LoadCommand and SaveCommand property, respectively.

8. Rebuild the application, and see if you can now load and save notes.
Create some notes, click Save, close the application, start it again, click
Load, and see if the saved notes reappear.
Exercise Excep.1

Project NoteBookV20

Purpose Use exceptions for error-handling in an MVVM application

Description The given application checks that notes cannot have the same title
(try it!), but the implementation is quite a mess… The handling is all
done in the set-part of the Title property in NoteDetailsViewModel,
with several calls to the model and the master-details view model

Steps Our aim is to clean up the error handling. This involves using exceptions for error
signaling and handling, and also to distribute various responsibilities to the proper
classes. An exception class TitleExistsException is included in the project.

1. In the NoteModel class, add checks to the methods Add and UpdateTitle,
such that a TitleExistsException is thrown if the new title exists
2. In the NoteMasterDetailsViewModel class, uncomment the method
UpdateTitle. See if you understand why the method is structured in this
particular way.
3. In the NoteDetailsViewModel class, go to the set-part of the Title
property. Remove ALL the code in the set-part, and replace it with a single
line of code:

_masterDetailsViewModel.UpdateTitle(value);

4. Clean up the NoteDetailsViewModel class a bit, since it no longer needs a

reference to the model (remove the instance field, and remove the
parameter from the constructor)
5. Rebuild the application and run it. See if the validation of titles still works
as before.
6. See if you can answer the below questions:
a. Which class detects and signals the error?
b. Which class assumes responsibility for handling the error?
c. Which class reports the error to the user?
7. If you have more time, see if you can update the application such that the
Title and Content fields in the view are only enabled if the user has
selected a Note in the list view.
Exercise MVVMStarter.1

Project MVVMStarterStudent

Purpose Integrate a domain class (Student) into the MVVMStarter framework

Description A domain class Student has been added to the MVVMStarter frame-
work application – now the subsequent steps described in the guide
need to be performed.

About the Student class:

 Some sample images have been added to the folder
Assets/Domain/Student, named “01” to “05”.
 The property PhotoID is included in the Student class, to make
it easy to set the photo used for a student. If you create a
TextBox in the Details view that is bound to PhotoID, the user
can type in a short string like “04”
 The aggregated property ImageSource will then contain the full
path to the image file, and can therefore be used in the Image-
Source property in the ItemViewModel class. Example: if the
value of PhotoID is set to “04”, the value of ImageSource will
become: "..\\..\\..\\Assets\\Domain\\Student\04.jpg". This is
the relative path to the images in the Assets/Domain/Student
folder

Steps 1. Use the guide “MVVMStarter Guide” on the MVVMStarter

website to integrate the Student class into the framework.
Remember to follow the steps carefully! It is always a good test
to try to build the project, after having completed a step.