使用JSONObject的Android应用程序无法在使用API​​ 19的设备上运行

Question

我正在尝试使用mysql数据库和php创建一个android应用程序。该代码在使用API​​ 21的设备上运行良好，但是在使用API​​ 19的设备上，出现此错误：

  

异常：java.lang.String类型的值异常无法转换为JSONObject

我看到了JSONArray的解决方案，但没有JSONObject的解决方案。

这是MainActivity.java：

public class MainActivity extends Activity {

EditText name, password;
String Name, Password;
Context ctx = this;
String NAME = null, PASSWORD = null, EMAIL = null;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    name = (EditText) findViewById(R.id.main_name);
    password = (EditText) findViewById(R.id.main_password);
}

public void main_register(View v) {
    startActivity(new Intent(this, Register.class));
}

public void main_login(View v) {
    Name = name.getText().toString();
    Password = password.getText().toString();
    BackGround b = new BackGround();
    b.execute(Name, Password);
}

class BackGround extends AsyncTask<String, String, String> {

    @Override
    protected String doInBackground(String... params) {
        String name = params[0];
        String password = params[1];
        String data = "";
        int tmp;

        try {
            URL url = new URL("https://something.com/login.php");
            String urlParams = "name=" + name + "&password=" + password;

            HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
            httpURLConnection.setDoOutput(true);
            OutputStream os = httpURLConnection.getOutputStream();
            os.write(urlParams.getBytes());
            os.flush();
            os.close();

            InputStream is = httpURLConnection.getInputStream();
            while ((tmp = is.read()) != -1) {
                data += (char) tmp;
            }

            is.close();
            httpURLConnection.disconnect();

            return data;
        } catch (MalformedURLException e) {
            e.printStackTrace();
            return "Exception: " + e.getMessage();
        } catch (IOException e) {
            e.printStackTrace();
            return "Exception: " + e.getMessage();
        }
    }

    @Override
    protected void onPostExecute(String s) {
        String err = null;
        try {

            JSONObject root = new JSONObject(s);
            JSONObject user_data = root.getJSONObject("user_data");

            NAME = user_data.getString("name");
            PASSWORD = user_data.getString("password");
            EMAIL = user_data.getString("email");
        } catch (JSONException e) {
            e.printStackTrace();
            err = "Exception: " + e.getMessage();
        }

        Intent i = new Intent(ctx, Home.class);
        i.putExtra("name", NAME);
        i.putExtra("password", PASSWORD);
        i.putExtra("email", EMAIL);
        i.putExtra("err", err);
        startActivity(i);

     }
  }
}

有什么解决办法吗？