the method onPostExecute simply was not executed, I have seen 16 at LogCat but I can not see 16 in LogCAT. I tried to debug it, it seemed that it goes to the first line of the class (package line) after return statement.

private class Client extends AsyncTask<Integer, Void, Integer> {
        protected Integer doInBackground(Integer... params) {
            Log.e(TAG,10+"");
            try {
                socket = new Socket(target, port);
                Log.e(TAG,11+"");
                oos = new ObjectOutputStream(socket.getOutputStream());
                Log.e(TAG,14+"");
                ois = new ObjectInputStream(socket.getInputStream());
                Log.e(TAG,15+"");
            } catch (UnknownHostException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
            Log.e(TAG,16+"");
            return 1;
        }

        protected void onPostExecute(Integer result) {
            Log.e(TAG,13+"");
            try {
                Log.e(TAG,12+"");
                oos.writeUTF(key);
                Log.e(TAG,13+"");
                if (ois.readInt() == OKAY) {
                    isConnected = true;
                    Log.e(TAG,14+"");
                }else{
                    Log.e(TAG,15+"");
                    isConnected = false;
                }
            } catch (IOException e) {
                e.printStackTrace();
                isClosed = true;
            }
        }
    }