Question

I’m using a thread so that I can show a progress dialog while my app loads some data. If there is an error it will stop the progress dialog and show the popup saying “error”. However I found out that alert dialogs cannot run inside a UI thread and that I need to use a Handler. Can someone with help with this issue? Here is my code. Thanks

verifyCode.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View arg0) {
    // TODO Auto-generated method stub
    final ProgressDialog progressDialog = ProgressDialog.show(
          Activate.this, "", "Loading...");    

    new Thread(new Runnable() {
        public void run() {
               try {
                     new AlertDialog.Builder(Activate.this)
                    .setTitle(getResources().getString(R.string.InvalidKey))
                    .setMessage(getResources().getString(
                    R.string.PleaseEntervalidRegistration)).setNeutralButton(
                    "OK", null).show();

                    progressDialog.dismiss();

                    //more code
     }).start();
}

Answer 1

You can’t make changes to UI element on non-UI threads. onClick will run on the UI thread, but since you spawn a Thread inside onClick then non-UI elements cannot be manipulated from inside that Thread. Move your AlertDialog and ProgressDialog calls to just prior to spawning the new Thread.

Also, as @lightblade suggested, If you need to do some sort of action which requires heavy background processing and UI manipulation based on that processing, then you should use AsyncTasks. It provides methods you can override for pre-processing, actual processing, post-processing, and updating progress.