从 AsyncTask 返回数据导致空指针错误

Question

我正在尝试执行我认为相当简单的任务来对我的服务器上的用户进行身份验证。我使用 AsyncTask 作为 Activity 的私有子类，但是当我在验证后尝试填充用户对象时，它始终将其设置为 null。 onPostExecute() 方法的调用方式是否有什么奇怪的地方导致了这种情况？我最初将 AsyncTask 作为自己的类，但遇到了同样的问题，所以我尝试使用私有子类来解决这个问题。有什么帮助吗？谢谢。

这是我的代码：

public class Testing extends Activity {

    private User user;

    public User getUser() {
        return this.user;
    }

    public void setUser(User value) {
        this.user = value;
    }

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        final ImageView iconImage = (ImageView) this.findViewById(R.id.image);
        final Button testButton = (Button) this.findViewById(R.id.testButton);
        final TextView text = (TextView) this.findViewById(R.id.text);
        iconImage.setImageResource(R.drawable.logo_real);
        testButton.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                LoginTask loginTask = (LoginTask) new LoginTask().execute(new Void[0]);
                text.setText(user.getFormattedFullName());
            }
        });
    }

    private class LoginTask extends AsyncTask<Void, Void, User> {

        public LoginTask() {
        }

        protected User doInBackground(Void... params) {
            User newUser = new User();
            try {
                System.out.println("testing task");
                HttpClient client = new DefaultHttpClient();
                HttpGet request = new HttpGet("http://10.0.2.2:8080/Dugout/[email protected]&PASSWORD=password");
                HttpResponse response = client.execute(request);
                HttpEntity entity = response.getEntity();
                InputStream is = entity.getContent();
                String message = "";
                String inputLine = "";
                BufferedReader bf = new BufferedReader(new InputStreamReader(is));
                while ((inputLine = bf.readLine()) != null) message+=inputLine;
                JSONObject returnedUser = new JSONObject(message);
                int userId = returnedUser.getInt("userId");
                boolean loginSuccess = returnedUser.getBoolean("login_success");
                String firstName = returnedUser.getString("firstName");
                String lastName = returnedUser.getString("lastName");
                newUser.setId(userId);
                newUser.setFirstName(firstName);
                newUser.setLastName(lastName);
                newUser.setLoginSuccess(loginSuccess);
                return newUser;
            } catch (Exception e) {
                newUser.setLoginSuccess(false);
                return newUser;
            }
        }

        protected void onPostExecute(User user) {
            setUser(user);
        }

    }

}

Answer 1

应该是

protected void onPostExecute(User user) {
    text.setText(user.getFormattedFullName());
}

您尝试在 AsyncTask 创建之前访问 user （重点是 doInBackground(..) 在后台运行因此线程不会阻塞 UI 线程）。