調用AsyncTask Android時崩潰

Question

我有一個wcf服務，根據輸入（檢查用戶登錄）返回true或false。 我正在嘗試在android應用中實現該功能，但是每當我按下按鈕時，應用就會崩潰。 這是代碼：

btnLogin.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub

            email = editEmail.getText().toString();
            pass = editPass.getText().toString();

            if(email.matches("") || pass.matches("")){
                txtresult.setText("Please fill in the information!");
                return;
            }


            if(!isConnected){
                txtresult.setText("You don't have internet connection!");
                return;
            }

            new MyTask().execute();

            if(status.equals("true")){
                //savePreferences();
                finish();
            }
            else{
                txtresult.setText("Wrong login information!");
            }
        }
    });

和AsyncTask：

public class MyTask extends AsyncTask<Void,Void,Void> {

    String email1 = editEmail.getText().toString();
    String pass1 = editPass.getText().toString();

    @Override
    protected Void doInBackground(Void... params) {
        HttpClient httpclient = new DefaultHttpClient();
        HttpGet httpGet = new HttpGet("http://wswob.somee.com/wobservice.svc/checkLogin/"+email1+"/"+pass1);
        HttpContext localContext = new BasicHttpContext();

        HttpResponse response;

          try {

            response = httpclient.execute(httpGet, localContext);
            HttpEntity entity = response.getEntity();
            status = EntityUtils.toString(entity);



          } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
          } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
          }

        return null;
    }
}

那正常，突然停止工作了……由於我有2周的經驗，我不確定如何調試。 有任何想法嗎？

Answer 1

這條線在這里：

if(status.equals("true")){

由於尚未分配status而崩潰，拋出NullPointerException。

根據定義，AsyncTask是異步的。 這意味着一旦您進行異步調用，代碼控件將立即返回並在另一個線程中開始異步工作。

正確的方法是使用AsyncTask回調onPostExecute() ，並在那里檢查您的狀態。

public class MyTask extends AsyncTask<Void,Void,Void> {

    String email1 = editEmail.getText().toString();
    String pass1 = editPass.getText().toString();

    @Override
    protected Void doInBackground(Void... params) {
        HttpClient httpclient = new DefaultHttpClient();
        HttpGet httpGet = new HttpGet("http://wswob.somee.com/wobservice.svc/checkLogin/"+email1+"/"+pass1);
        HttpContext localContext = new BasicHttpContext();

        HttpResponse response;

          try {

            response = httpclient.execute(httpGet, localContext);
            HttpEntity entity = response.getEntity();
            status = EntityUtils.toString(entity);



          } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
          } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
          }

        return null;
    }

    @Override
    protected Void onPostExecute(Void result){
        super.onPostExecute(result);
        //TODO: your code here. check your status and handle from there
    }
}