Xamarin.forms: [Bug, iOS] Frame shadow layer not properly removed

[jfversluis]

Description

By the merge of #7518 there is now a bug where Frames aren't properly removed. At leased when used in a BindableLayout with the shadow on. This is discovered while reviewing the empty view implementation on the BindableLayout.

Investigation

I have tried to fix it, but can't quite get it right. When you add a Dispose to the FrameRenderer on iOS like this:

                protected override void Dispose(bool disposing)
        {
            if (_isDisposed)
                return;

            if (disposing && _shadowView != null)
            {
                _shadowView.RemoveFromSuperview();
                _shadowView.Dispose();
                _shadowView = null;
            }

            _isDisposed = true;

            base.Dispose(disposing);
        }

It seems a bit better, but not entirely fixed. See below on what that does to the behavior.

Notice how the first item is removed and the shadow disappears, but there still remains an artefact at the bottom. It almost seems like the boxes are removed in the opposite direction.

Steps to Reproduce

1. Start Gallery app
2. Go to BindableLayout Gallery - Legacy
   2 a. If the empty view PR (#7686) got merged in the meantime, remove the HasShadow="false" from the Frame on this page
3. Remove an item and observe that an empty yellow box stays behind

Expected Behavior

Frame is entirely removed from the layout, no empty yellow box is shown

Actual Behavior

The frame outline (yellow box) is still visible as an artefact on the screen

Basic Information

• Version with issue: current master branch
• Last known good version: Before #7518
• Platform Target Frameworks:
  
  
  
  • iOS: 13.2.2 but all are affected
  
  

Screenshots

[jfversluis]

I totally see this happening, thank you for your excellent report @jfversluis!

[samhouts]

@jfversluis Did you happen to fix this, by any chance? 😁

[jfversluis]

Well waddayaknow! I did! Assuming that the Frame fixes were merged and in master currently. Retested it and didn't see this problem anymore.

Also checked 4.5, not happening there anymore either