java - 异步任务中的对话框错误

Question

当我尝试显示异步任务的工作对话框时，出现以下错误:java.lang.reflect.InvocationTargetException异常java.lang.NullPointerException

activity 和 asynctask 的代码是:

public class MainActivity extends Activity {

    private ControlLogin ctlLogin;
    private ProgressDialog dialog;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login);

        ctlLogin = (ControlLogin)findViewById(R.id.controlLogin);

        ctlLogin.setOnLoginListener(new OnLoginListener()
    {
        @Override
        public void onLogin(String email, String password, Boolean saveAccount){


            ProgressDialog dialog = new ProgressDialog(getApplicationContext());
            dialog.setMessage("Signing...");
            dialog.setIndeterminate(true);
            dialog.setCancelable(false);

            new Login().execute(email, password);
        }
    });



    }

    public class Login extends AsyncTask<String, Float, CloudApp> {

        protected void onPreExecute(){
            dialog.show();
        }
        @Override
        protected CloudApp doInBackground(String... arg0) {
            CloudApp api = new CloudAppImpl(arg0[0], arg0[1]);
            return api;
        }

        protected void onPostExecute(CloudApp api){

            dialog.dismiss();
            try {
                CloudAppAccount acc = api.getAccountDetails();
                Toast toast = Toast.makeText(getBaseContext(), "test: " + acc.getEmail(), Toast.LENGTH_LONG);
                toast.show();
            } catch (CloudAppException e) {
                e.printStackTrace();
            }
        }

    }

}

有什么帮助吗？？？谢谢!!

Answer 1

您通过在 onLogin(...) 方法中定义局部变量 dialog 来隐藏您的代码中的成员 dialog。因此，dialog 永远不会被初始化为任何东西，这就是为什么您在 Login 类中获得 NPE 的原因。

    @Override
    public void onLogin(String email, String password, Boolean saveAccount){

        //remove the leading ProgessDialog here...it is hiding your member 'dialog'
        //dialog = new ProgressDialog(getApplicationContext());
        ProgressDialog dialog = new ProgressDialog(getApplicationContext());
        dialog.setMessage("Signing...");
        dialog.setIndeterminate(true);
        dialog.setCancelable(false);

        new Login().execute(email, password);
    }