Question

当我尝试显示asynctask的工作对话框时，我收到以下错误： java.lang.reflect.InvocationTargetException 显示java.lang.NullPointerException

活动和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();
            }
        }

    }

}

任何帮助???谢谢！

Answer 1

您通过在dialog方法中定义局部变量dialog，将您的成员onLogin(...)隐藏在代码中。因此，dialog永远不会初始化为任何内容，这就是您在Login课程中获得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);
    }

Answer 2

当你解雇它时，你确定你的对话存在吗？我认为在onLogin中，您重新创建一个与活动字段变量同名的新对话框变量。

protected void onPostExecute(CloudApp api) {

            dialog.dismiss(); // this one is not initialized
            try {
                CloudAppAccount acc = api.getAccountDetails();

你可以安全地玩：

 if (dialog != null) dialog.dismiss();

asynctask中的对话框错误

2 个答案: