Xamarin android - How to add addOnPreDrawListener for viewgroup in c#

Question

I am tryign to create a extended FAB menu in xamarin android(c#). I have following this article(https://blog.stylingandroid.com/floating-action-button-part-3/), convered all from java code to c# except adding "addOnPreDrawListener" listener for fabContainer(ref to below code)

 final ViewGroup fabContainer = (ViewGroup) findViewById(R.id.fab_container);
 fabContainer.getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
        @Override
        public boolean onPreDraw() {
            fabContainer.getViewTreeObserver().removeOnPreDrawListener(this);
            offset1 = fab.getY() - fabAction1.getY();
            fabAction1.setTranslationY(offset1);
            offset2 = fab.getY() - fabAction2.getY();
            fabAction2.setTranslationY(offset2);
            offset3 = fab.getY() - fabAction3.getY();
            fabAction3.setTranslationY(offset3);
            return true;
        }
    });

I am tring to do following but OnPreDrawListener class is not available in xamarin android.

  ViewTreeObserver treeObserver = fabContainer.ViewTreeObserver;
        treeObserver.AddOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener
        {
        });

Please guide me.

Thanks

@paul

Answer 1

How to add addOnPreDrawListener for viewgroup in c#

As @Dharmik Patel said, you could implement the ViewTreeObserver.IOnPreDrawListener in your Activity

public class MainActivity : AppCompatActivity, ViewTreeObserver.IOnPreDrawListener
{
    ...
    fabContainer.ViewTreeObserver.AddOnPreDrawListener(this);
    ...

    public bool OnPreDraw()
    {
        //Do your logic 
    }
}

Alternative choice :

class MyOnPreDrawListener : Java.Lang.Object, ViewTreeObserver.IOnPreDrawListener
{
    private MainActivity mainActivity;

    public MyOnPreDrawListener(MainActivity mainActivity)
    {
        this.mainActivity = mainActivity;
    }

    public bool OnPreDraw()
    {
       //Do your logic 
    }
}

fabContainer.ViewTreeObserver.AddOnPreDrawListener(new MyOnPreDrawListener(this));