ProgressDialog not shown when AsyncTask.get() called [duplicate]

Question

Possible Duplicate:
AsyncTask block UI threat and show progressbar with delay

I want to show a progressDialog while retrieving JSON from any server. So I had used AsyncTask as a solution (not sure any different way out).

Everything is fine, the ProgressDialog works properly until I call .get() method using AsyncTask instance. I suppose it's blocking UI somehow. Here is my AsyncTask:

public class myAsync extends AsyncTask<String, String, List> {

    String message; // for dialog message
    ProgressDialog progress; 
    Intent myIntent;
    Context ctx;

    public myAsync(String message, Context ctx) {
        this.message = message;
        this.ctx = ctx;
        progress = new ProgressDialog(ctx);
    }

    @Override
    protected void onPreExecute() { 
        progress.setMessage(message);
        progress.setIndeterminate(true);
        progress.setCancelable(false);
        progress.show();    
    }

    @Override
    protected List doInBackground(String... params) {
        //returns any list after the task
        return anyList; 
    }

    @Override
    protected void onPostExecute(List result) {
        if(progress.isShowing())
            progress.dismiss();
    }
}

And here is myActivity which is calls AsyncTask:

myAsync asyncTask = new myAsync("Loading...", this);
asyncTask.execute("Any string", "Other string");
asyncTask.get(); // If I comment out this line, ProgressDialog works

After execute, when I tried to log the result from doInBackground and onPostExecute both there is no problem. But if I want to get with .get() the result ProgressDialog is not shown or shown so little time (maybe 0.2 seconds)

What's the problem?

Answer 1

Yes, get() waits if necessary for the computation to complete, and then retrieves its result. This means, that you are blocking your UI thread, waiting for the result.

Solution: Don't call get

Usually, you will call a function (callback) in the postExecute.

Answer 2

Calling .get() changes your AsyncTask into an effective "SyncTask" as it causes the current thread (which would be the UI thread) to wait until the AsyncTask has finished its processing. Since you are now blocking the UI thread the call to the ProgressDialog's .show() method never gets a chance to allow the dialog to draw itself the screen.

Removing the call will allow it to run properly in the background.

If you need to do processing after the task has completed I suggest you either put it inside the onPostExecute method itself or use a callback to the Activity from onPostExecute.