What is iOS UIScrollView's equivalent to Android's OnDraw(Canvas canvas)?

I'm trying to write the iOS equivalent of my Android code for a ScrollViewRenderer.

In Android I have the following method which is called each time the scrollview is scrolled, allowing me to update the UI:

protected override void OnDraw(Canvas canvas)
{
    ...
    ...
    base.OnDraw(canvas);
}

In iOS I'm trying to do the same thing with the following method. However it is only called when the page loads and not upon each scroll event:

public override void Draw(CoreGraphics.CGRect rect)
{
    ...
    ...
    base.Draw(rect);
}

I have a few questions:

• What is the iOS equivalent method I should be using instead of Draw?
• Will this method provide me with a canvas to draw on? I want to display a scrolling bitmap, but can't do much with just a CGRect.
• How can I get the current ScrollY? In Android this is a Property of the Renderer class. I can't find it in iOS.