ProgressDialog not appearing

I have code that starts a ProgressDialog inside an AsyncTask, it looks like this:

class RetrieveApps extends AsyncTask<String, Void, List<ApplicationInfo>> {
    PackageManager pm;

    @Override
    protected List<ApplicationInfo> doInBackground(String...params) {
        dialog = ProgressDialog.show(Apps.this,
                "Retreiving Application list",
                "Retrieving list of installed applications", true);
        pm = getPackageManager();
        return pm.getInstalledApplications(PackageManager.GET_META_DATA);
    }
    @Override
    protected void onPostExecute(List<ApplicationInfo> result) {
        for(ApplicationInfo nfo : result){
            Drawable icon = nfo.loadIcon(pm);
            String name = nfo.loadLabel(pm).toString();
            if(name != null && icon != null){
                apps.add(new App(name, icon));
            }
        }
        dialog.dismiss();
    }

}

I'm getting a RuntimeException saying

Can't create handler inside thread that has not called Looper.pr开发者_高级运维epare()

It points at the line where ProgressDialog.show() was called.

public class RetrieveApps extends AsyncTask<String, Void, List<ApplicationInfo>> {
    PackageManager pm;

    @Override
    protected List<ApplicationInfo> doInBackground(String...params) {

        pm = getPackageManager();
        return pm.getInstalledApplications(PackageManager.GET_META_DATA);
    }
    @Override
    protected void onPostExecute(List<ApplicationInfo> result) {
        for(ApplicationInfo nfo : result){
            Drawable icon = nfo.loadIcon(pm);
            String name = nfo.loadLabel(pm).toString();
            if(name != null && icon != null){
                apps.add(new App(name, icon));
            }
        }
        dialog.dismiss();
    }

    @Override
    protected void onPreExecute(){
      dialog = ProgressDialog.show(Apps.this,
                "Retreiving Application list",
                "Retrieving list of installed applications", true);

    }

}

try the above class , i moved the dialog creation in the onPreExecute method which runs on UI thread

Remember onPreExecute , onPostExecute and onProgressUpdate methods run on UI thread doInBackground method runs on non-UI thread

Your dialog creation is suppose to be on the UI thread so that I can post back progress to the dialog, implement onPreExecute() with your dialog creation code. To post progress call and implement onProgressUpdate (Progress... values).

Move this:

dialog = ProgressDialog.show(Apps.this,
        "Retreiving Application list",
        "Retrieving list of installed applications", true);

To the onPreExecute method.

onPreExecute (and onPostExecute, where you will cancel the dialog) happens on the UI thread and therefore can make UI changes. doOnBackground works in a different thread and therefore can't make UI changes.