Toast created in an IntentService never goes away

The problem is that IntentService is not running on the main application thread. you need to obtain a Handler for the main thread (in onCreate()) and post the Toast to it as a Runnable.

the following code should do the trick:

@Override
public void onCreate() {
    super.onCreate();
    mHandler = new Handler();
}

@Override
protected void onHandleIntent(Intent intent) {
    mHandler.post(new Runnable() {            
        @Override
        public void run() {
            Toast.makeText(MyIntentService.this, "Hello Toast!", Toast.LENGTH_LONG).show();                
        }
    });
}

This works for me:

public void ShowToastInIntentService(final String sText) {
    final Context MyContext = this;

    new Handler(Looper.getMainLooper()).post(new Runnable() {
        @Override
        public void run() {
            Toast toast1 = Toast.makeText(MyContext, sText, Toast.LENGTH_LONG);
            toast1.show();
        }
    });
};

IntentService will create a thread to handle the new intent, and terminated it immediately once the task has done. So, the Toast will be out of controlled by a dead thread.

You should see some exceptions in the console when the toast showing on the screen.

For people developing in Xamarin studio, this is how its done there:

Handler handler = new Handler ();
handler.Post (() => {
    Toast.MakeText (_Context, "Your text here.", ToastLength.Short).Show ();
});