Question

I am a fairly beginner in Android Development. I am developing an application that extensively relays on Webservice calls. First screen takes username and password and validates the user by calling the Webservice. If U/P is valid, then I need to fire up the 2nd activity. In that 2nd activity, I need to do 3 calls. But I haven’t gotten to the 2nd part yet. In fact, I haven’t completed the full coding yet. But I wanted to test if the app is working as far as I’ve come through.

When calling webserivce, I am showing alert dialog. But the app is crashing somewhere.
The LoginActivity shows up. When I enter U/P and press Login Button, it crashes.

My classes:

TaskHandler.java

 public class TaskHandler {

private String URL;
private User userObj;
private String results;
private JSONDownloaderTask task; ;

public TaskHandler( String url, User user) {
    this.URL = url;
    this.userObj = user;
}

public String handleTask() {
    Log.d("Two", "In the function");
    task = new JSONDownloaderTask();
    Log.d("Three", "In the function");
    task.execute(URL);
    return results;
}

private class JSONDownloaderTask extends AsyncTask<String, Void, String> {

    private String username;// = userObj.getUsername();
    private String password; //= userObj.getPassword();

    public  HttpStatus status_code;

    public JSONDownloaderTask() {
        Log.d("con", "Success");
        this.username = userObj.getUsername();
        this.password = userObj.getPassword();

        Log.d("User" + this.username , " Pass" + this.password);
    }

    private AsyncProgressActivity progressbar = new AsyncProgressActivity();

    @Override
    protected void onPreExecute() {
        progressbar.showLoadingProgressDialog();
    }

    @Override
    protected String doInBackground(String... params) {

        final String url = params[0]; //getString(R.string.api_staging_uri) + "Authenticate/";

        // Populate the HTTP Basic Authentitcation header with the username and password
        HttpAuthentication authHeader = new HttpBasicAuthentication(username, password);
        HttpHeaders requestHeaders = new HttpHeaders();
        requestHeaders.setAuthorization(authHeader);
        requestHeaders.setAccept(Collections.singletonList(MediaType.APPLICATION_JSON));

        // Create a new RestTemplate instance
        RestTemplate restTemplate = new RestTemplate();

        restTemplate.getMessageConverters().add(new MappingJacksonHttpMessageConverter());

        try {
            // Make the network request
            Log.d(this.getClass().getName(), url);

            ResponseEntity<Message> response = restTemplate.exchange(url, HttpMethod.GET, new HttpEntity<Object>(requestHeaders), Message.class);
            status_code =  response.getStatusCode();
            return response.getBody().toString();
        } catch (HttpClientErrorException e) {

            status_code = e.getStatusCode();
            return new Message(0, e.getStatusText(), e.getLocalizedMessage(), "error").toString();
        } catch ( Exception e ) {
            Log.d(this.getClass().getName()  ,e.getLocalizedMessage());
            return "Unknown Exception";
        }
    }


    @Override
    protected void onPostExecute(String result) {
        progressbar.dismissProgressDialog();


        switch ( status_code ) {
        case UNAUTHORIZED:
            result =  "Invalid username or passowrd"; break;
        case ACCEPTED:
            result = "Invalid username or passowrd" + status_code; break;
        case OK:
            result = "Successful!"; break;
        }
    }
}
}

AsycProgressActivity.java

public class AsyncProgressActivity  extends Activity {

protected static final String TAG = AsyncProgressActivity.class.getSimpleName();

private ProgressDialog progressDialog;
private boolean destroyed = false;

@Override
protected void onDestroy() {
    super.onDestroy();
    destroyed = true;
}

public void showLoadingProgressDialog() {
    Log.d("Here", "Progress");
    this.showProgressDialog("Authenticating...");
    Log.d("Here", "afer p");
}

public void showProgressDialog(CharSequence message) {
    Log.d("Here", "Message");
    if (progressDialog == null) {
        progressDialog = new ProgressDialog(this);
        progressDialog.setIndeterminate(true);
    }
    Log.d("Here", "Message 2");

    progressDialog.setMessage(message);
    progressDialog.show();
}

public void dismissProgressDialog() {
    if (progressDialog != null && !destroyed) {
        progressDialog.dismiss();
    }
}
}

LoginActivity.java

public class LoginActivity extends AsyncProgressActivity implements OnClickListener {

Button login_button;
HttpStatus status_code;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //this.requestWindowFeature(Window.FEATURE_NO_TITLE);

    setContentView(R.layout.main);

    login_button = (Button) findViewById(R.id.btnLogin);
    login_button.setOnClickListener(this);
    ViewServer.get(this).addWindow(this); 
}

public void onDestroy() {  
    super.onDestroy();  
    ViewServer.get(this).removeWindow(this);  
}  

public void onResume() {  
    super.onResume();  
    ViewServer.get(this).setFocusedWindow(this);  
}  

public void onClick(View v) {
    if ( v.getId() == R.id.btnLogin ) {

        User userobj = new User();
        String result;
        userobj.setUsername( ((EditText) findViewById(R.id.username)).getText().toString());
        userobj.setPassword(((EditText) findViewById(R.id.password)).getText().toString() );


        TaskHandler handler = new TaskHandler(getString(R.string.api_staging_uri) + "Authenticate/", userobj);
        Log.d(this.getClass().getName(), "One");
        result = handler.handleTask();
        Log.d(this.getClass().getName(), "After two");
        Utilities.showAlert(result, LoginActivity.this);
    }
}

Utilities.java

public class Utilities {

public static void showAlert(String message, Context context) {

    AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(context);
    alertDialogBuilder.setTitle("Login");

    alertDialogBuilder.setMessage(message)
                      .setCancelable(false)
                      .setPositiveButton("OK",new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog,int id) {
                            dialog.dismiss();
                            //dialog.cancel();
                        }
                       });
    alertDialogBuilder.setIcon(drawable.ic_dialog_alert);

    // create alert dialog
    AlertDialog alertDialog = alertDialogBuilder.create();

    // show it
    alertDialog.show(); 
}
 }

EDIT: More info

I tried to add Logging step by step to see where its crashing. It looks like its crashing here. Because its not showing the log message after this.

        Log.d("Here", "Message");
    if (progressDialog == null) {
        progressDialog = new ProgressDialog(this);
        progressDialog.setIndeterminate(true);
    }
    Log.d("Here", "Message 2");

Message 2 is not showing up in the log, but Message shows up.

Answer 1

I think the issue is your handleTask method:

public String handleTask() {
    Log.d("Two", "In the function");
    task = new JSONDownloaderTask();
    Log.d("Three", "In the function");
    task.execute(URL);
    return results;
}

You are kicking off an AsyncTask which will populate the results variable in another thread when the task is finished. However, you are returning this value right away and immediately using it to build an AlertDialog. This variable probably has not been populated by the background thread yet and may still be null.

EDIT: You probably shouldn’t call showAlert in onClick. Instead, you should call it in onPostExecute.