Question

This is the wireframe of how my class is built:

public class HelloWorldActivity extends Activity 
{
    private ProgressDialog progressdialog;

    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);        
        setContentView(R.layout.main);        
    }       

    private class AuthenticateUserTask extends AsyncTask<Void,Void,String>
    {
        protected String doInBackground(Void... params)
        {
            //do something  
        }

        protected void onPostExecute(String result)
        {
            if (result.equals("success"))
                //do something
           else
           {               
               progressdialog.dismiss(); //this throws a null pointer exception
               /*
               When above line is commented to allow execution of app, Toast never shows on screen
               however no errors are recorded in the log
               */
               Toast.makeText(getApplicationContext(),"Login failed",Toast.LENGTH_SHORT);
           }
        }                   
    }   

    public void login(View v)
    {       
        progressdialog.show(HelloWorldActivity.this,"","Logging in...",true);
        new AuthenticateUserTask().execute();
    }   
}

I’m sorry if it seems I’m asking two questions in one thread, but I suspect the solution is similar for both.

Within onPostExecute:
1. If login fails and I do progressdialog.dismiss(), a null pointer exception is thrown and application crashes.
2. If I remove the ProgressDialog and attempt to show a Toast, nothing show up on the screen, however no exception or error is recorded either.

EDIT
I found the solution to my first problem in another thread here.
I had to display the ProgressDialog in an onPreExecute method.

Answer 1

To get the ProgressDialog to show, override the following method in your AsyncTask:

protected void onPreExecute() {
  progressdialog = ProgressDialog.show( HelloWorldActivity.this, "", "Logging in..." );
}

Note: you need to remove this line from your login() method:

progressdialog.show(HelloWorldActivity.this,"","Logging in...",true);

The reason your Toast is not showing is that you forgot to call .show():

Toast.makeText(getApplicationContext(),"Login failed",Toast.LENGTH_SHORT).show();