调用AsyncTask Android时崩溃

Question

I have one wcf service that returns true or false depending on the input (to check user log in). I'm trying to implement that in android app but whenever I press the button, the application crashes. This is the code:

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!");
            }
        }
    });

And the 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;
    }
}

That worked normal and suddenly stopped working… I'm not really sure how to debug due to my 2 weeks experience. Any ideas?

Answer 1

this line here:

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

is crashing because status hasn't been assigned yet, throwing a NullPointerException.

AsyncTasks are, by definition, asynchronous. This means that once you make the async call, the code control will return immediately and start the async work in another thread.

The correct way to do this is to use the AsyncTask callback onPostExecute() , and check your status there instead.

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
    }
}