I. Preparations

1. Development Platform and SDK Download

Wechat Open Platform

https://open.weixin.qq.com

Download SDK

Wechat Payment Demo Download

http://pay.weixin.qq.com/wiki/doc/api/app.php?chapter=11_1

 

2. Creating Applications

Creating Mobile Applications to Get AppID AppSecret

To obtain payment function, it also needs developer qualification certification, 300 RMB / year fee, which seems to be the only fee in the open platform.

 

3. Android Mainfest File Modification

Jurisdiction

<uses-permission android:name="android.permission.INTERNET"/> 
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>
<uses-permission android:name="android.permission.READ_PHONE_STATE"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

　　

II. Business processes

Interaction between merchant system and Wechat payment system

Step 1: User chooses goods in APP, submits orders, and chooses Wechat to pay.

Step 2: The merchant receives the user's payment form in the background and invokes the unified order interface of Wechat payment. See also[ Unified Order API].

Step 3: Unified single interface returns normal prepay_id, and then regenerates the signature according to the signature specification, then transfers the data to APP. The fields participating in the signature are appId, partnerId, prepayId, nonceStr, timeStamp, package. Note: The value format of package is Sign=WXPay

Step 4: Merchant APP calls Wechat Payment. See this chapter for api[ Description of development steps on app side]

Step 5: Business background receives payment notification. api see[ Payment Result Notification API]

Step 6: Business background query payment results. api[ Query Order API]

 

III. Development

1. Registration Application

final IWXAPI msgApi = WXAPIFactory.createWXAPI(this, null);
msgApi.registerApp(Constants.APP_ID);

　　

2. Call Unified Payment Single Interface and Return PrepayID

private class GetPrepayIdTask extends AsyncTask<Void, Void, Map<String,String>> {
 
        private ProgressDialog dialog;
 
        @Override
        protected void onPreExecute() {
            dialog = ProgressDialog.show(PayActivity.this, getString(R.string.app_tip), getString(R.string.getting_prepayid));
        }
 
        @Override
        protected void onPostExecute(Map<String,String> result) {
            if (dialog != null) {
                dialog.dismiss();
            }
            sb.append("prepay_id\n"+result.get("prepay_id")+"\n\n");
            show.setText(sb.toString());
            resultunifiedorder=result;
        }
 
        @Override
        protected void onCancelled() {
            super.onCancelled();
        }
 
        @Override
        protected Map<String,String>  doInBackground(Void... params) {
            String url = String.format("https://api.mch.weixin.qq.com/pay/unifiedorder");
            String entity = genProductArgs();
            Log.e("orion",entity);
            byte[] buf = Util.httpPost(url, entity);
            String content = new String(buf);
            Log.e("orion", content);
            Map<String,String> xml=decodeXml(content);
            return xml;
        }
    }

3. Setting parameters of PayReq request and sending payment request

//Setting parameters for PayReq requests
private void genPayReq() {
        req.appId = Constants.APP_ID;
        req.partnerId = Constants.MCH_ID;
        req.prepayId = resultunifiedorder.get("prepay_id");
        req.packageValue = "prepay_id="+resultunifiedorder.get("prepay_id");
        req.nonceStr = genNonceStr();
        req.timeStamp = String.valueOf(genTimeStamp());
 
        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);
        sb.append("sign\n"+req.sign+"\n\n");
        show.setText(sb.toString());
        Log.e("orion", signParams.toString()); 
    }

 

//Send requests
msgApi.sendReq(req);

　

4. Processing Result Callback

IWXAPIEventHandler Interface for Implementing Wechat API

api.handleIntent(getIntent(), new IWXAPIEventHandler);

Processing request callbacks in onResp(BaseResp resp) of IWXAPIEventHandler

@Override
    public void onResp(BaseResp resp) {
        Log.d(TAG, "onPayFinish, errCode = " + resp.errCode);
 
        if (resp.getType() == ConstantsAPI.COMMAND_PAY_BY_WX) {
                    //Handling PayReq callbacks
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle(R.string.app_tip);
        builder.setMessage(getString(R.string.pay_result_callback_msg, resp.errStr +";code=" + String.valueOf(resp.errCode)));
        builder.show();
    }
}