####1.服务器首先联网获取ACCESS_TOKEN，然后根据获取到的access_token，生成预支付订单； ####2.客户端会去访问服务器获取预支付订单，主要是 prepayId、nonceStr 这两个参数； ####3.客户端获取到以上两个参数后； //调起微信支付 private void sendPayReq(String prepayId, String nonceStr) {
PayReq req = new PayReq();
req.appId = Constants.WX_APPID;
req.partnerId = Constants.WX_PARTNER_ID;
req.prepayId = prepayId;
req.nonceStr = nonceStr;
req.timeStamp = String.valueOf(SystemClock.currentThreadTimeMillis());
req.packageValue = "Sign=WXPay";
List<NameValuePair> signParams = new LinkedList<NameValuePair>();
signParams.add(new BasicNameValuePair("appid", req.appId));
signParams.add(new BasicNameValuePair("noncestr", req.nonceStr));
signParams.add(new BasicNameValuePair("package", req.packageValue));
signParams.add(new BasicNameValuePair("partnerid", req.partnerId));
signParams.add(new BasicNameValuePair("prepayid", req.prepayId));
signParams.add(new BasicNameValuePair("timestamp", req.timeStamp));
req.sign = genAppSign(signParams);
// 在支付之前，如果应用没有注册到微信，应该先调用IWXMsg.registerApp将应用注册到微信
api.sendReq(req);
}
//生成签名方法
private String genAppSign(List<NameValuePair> params) {
StringBuilder sb = new StringBuilder();
for (int i = 0; i < params.size(); i++) {
sb.append(params.get(i).getName());
sb.append('=');
sb.append(params.get(i).getValue());
sb.append('&');
}
sb.append("key=");
sb.append(Constants.WX_APP_KEY);
String sign = MD5.getMessageDigest(sb.toString().getBytes()).toUpperCase();
return sign;
}