Android - Waiting till view is laid on screen without any guesswork

Question

I am creating a TutorialManager that handles all the user tutoring for app usage.

I have a ViewGroup that adds views to itself including a GridView that is filled with items after onMeasure() is called.

I am calling TutorialManagers method that's supposed to perform an action on the gridview but it needs to know when the gridview is filled in order to use any of it items

I added a callback method on the ViewGroup that is called right after all the view have been added

The problem is that the TutorialManager needs to know the X and Y coordinate of the views in order to highlight them using ShowCaseView

I've added a workaround using postDelayed(action, 100); which seems to work on my handset but what if on some device the view layout takes more than 100ms? It'll screw up the whole tutoring system.

I can't figure out any other way than creating a custom view that has a callback method which is called after the views position is known.

What's the common way of handling the issue that the laying view on screen is happening asynchronously?

Answer 1

You can try using an OnGlobalLayoutListener which fires whenever there is a layout change (Ie, your GridView and children have been added and measured. So where ever you initialize the GridView do this:

LayoutListener mLayoutListener = new LayoutListener;
mGridView.getViewTreeObserver().addOnGlobalLayoutListener(mLayoutListener);

private class LayoutListener implements OnGlobalLayoutListener {
    @Override
    public void onGlobalLayout() {
        ...Do your calculations here...

        mGridView.getViewTreeObserver().removeOnGlobalLayoutListener(this); //If you only need this to execute once.
    }
}

Note this will be called quite often. I'd recommend removing as soon as you don't need it.