Exception "Can't create handler inside thread that has not called looper prepare" in android app

Question

I'm working on my first android app and I'm trying to use Quickblox.com as my backend.

In order to use it, I need to authorize the app by creating a session using their SDK.

So, I have the following code:

// Initialize QuickBlox application with credentials.
            QBSettings.getInstance().fastConfigInit(Consts.APP_ID, Consts.AUTH_KEY, Consts.AUTH_SECRET);

            // Authorize application

            QBAuth.createSession(new QBCallback() {
                @Override public void onComplete(Result result) {}
                @Override
                public void onComplete(Result result, Object context) {
                    if (result.isSuccess()) {
                        showMainScreen();
                    } else {
                        // print errors that came from server
                        Toast.makeText(getBaseContext(), result.getErrors().get(0), Toast.LENGTH_SHORT).show();
                        progressBar.setVisibility(View.INVISIBLE);
                    }

                }
            }, QBQueries.QB_QUERY_AUTHORIZE_APP);

This code works well with an emulator, but it doesn't work if I try with a real android phone. I have a connection timeout error. I think I need to make this kind of requests (Web Services) in the background right?

So I tried to use the AsyncTask to make the request to QB in the background, and changed the code to this:

new AsyncTask<Void, Void, Void>() {

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

            // Initialize QuickBlox application with credentials.
            QBSettings.getInstance().fastConfigInit(Consts.APP_ID, Consts.AUTH_KEY, Consts.AUTH_SECRET);

            // Authorize application

            QBAuth.createSession(new QBCallback() {
                @Override public void onComplete(Result result) {}
                @Override
                public void onComplete(Result result, Object context) {
                    if (result.isSuccess()) {
                        showMainScreen();
                    } else {
                        // print errors that came from server
                        Toast.makeText(getBaseContext(), result.getErrors().get(0), Toast.LENGTH_SHORT).show();
                        progressBar.setVisibility(View.INVISIBLE);
                    }
                }
            }, QBQueries.QB_QUERY_AUTHORIZE_APP);
            return null;
        }
    }.execute();

I've seen a lot of similar questions here at SO, but I can't seem to find an answer that works with my code. I saw that functions that deal with the UI need to be called from the main thread, so I suppose that the code I have inside

onComplete(Result result, Object context)

should be inside a block like this right?

runOnUiThread(new Runnable() 
{
    public void run() 
    {
        // code here
    }
}); 

But I tried that as well and it didn't work. Any guesses?

I believe the problem is not because of the Toast and showMainScreen(). It still fails with this code:

// Initialize QuickBlox application with credentials.
            QBSettings.getInstance().fastConfigInit(Consts.APP_ID, Consts.AUTH_KEY, Consts.AUTH_SECRET);

            QBAuth.createSession(new QBCallback() {

                @Override
                public void onComplete(Result arg0, Object arg1) {
                    // TODO Auto-generated method stub

                }

                @Override
                public void onComplete(Result arg0) {
                    // TODO Auto-generated method stub

                }
            }, QBQueries.QB_QUERY_AUTHORIZE_APP);

But it doesn't fail if I just create the QBCallback object, without passing it to the QBAuth.createSession function.

Answer 1

You can't show a Toast in doInBackground of AsyncTask as it is a different threat and not the main UI thread.

To show a toast or any UI related task you have to do it in onPostExecute method of AsyncTask.

What you can do is

    new AsyncTask<Void, Void, boolean>() {

            @Override
            protected boolean doInBackground(Void... params) {

                // Initialize QuickBlox application with credentials.
                QBSettings.getInstance().fastConfigInit(Consts.APP_ID, Consts.AUTH_KEY, Consts.AUTH_SECRET);
                boolean res = false;

                // Authorize application

                QBAuth.createSession(new QBCallback() {
                    @Override public void onComplete(Result result) {}
                    @Override
                    public void onComplete(Result result, Object context) {
                        if (result.isSuccess()) {
                            //showMainScreen();
                            res = true
                        } 
                        //else {
                            // print errors that came from server
                            //Toast.makeText(getBaseContext(), result.getErrors().get(0),                   //Toast.LENGTH_SHORT).show();
                            //progressBar.setVisibility(View.INVISIBLE);
                        //}
                    }
                }, QBQueries.QB_QUERY_AUTHORIZE_APP);
                return res;
            }

          protected void onPostExecute(boolean result) {
             if(result) {
                showMainScreen();
             } else {
                Toast.makeText(getBaseContext(), result.getErrors().get(0),                   Toast.LENGTH_SHORT).show();
                            progressBar.setVisibility(View.INVISIBLE);
             }
          }
        }.execute();

Answer 2

You don't need to use AsyncTasks, because all operations already perform in background.

And also this one

 QBAuth.createSession(new QBCallback() {

it performs request in background to QB and call callback in Main thread.

Could you explain what 'connection timeout error' you got. Is there anything in log?