[iOS] UIScrollView Custom Handler's Zoom View changes position after button click or resuming from OnSleep state

[Takashi125]

Description

I'm currently porting our Xamarin.Forms application that has a custom ScrollViewer implementing UIKit's ScrollView. But there's a bug that whenever the screen's zoomed and the app resumes from a sleep state, the view changes its position, shrinks its ScrollHeight , and zooming out positions the page on the upper left of the screen.

Update: Pressing the button inside the grid while on zoomed state also produces the same bug.

Steps to Reproduce

1. Load the repro project (including setting an app identifier if testing on a physical device)
2. Start the application on an iOS device or simulator
3. Pinch zoom in the app
4. Go back to the home screen, then go back to the app
5. ScrollView height shrinks, and when you pinch zoom out, the main page's offset moves to the upper left of the screen

Link to public reproduction project repository

https://github.com/Takashi125/UIScrollViewBugProj

Version with bug

7.0.101 , 8.0.3 GA

Is this a regression from previous behavior?

Yes, this used to work in Xamarin.Forms

Last version that worked well

Unknown/Other

Affected platforms

iOS

Affected platform versions

iOS 17, iOS 15

Did you find any workaround?

No response

Relevant log output

No response

[Takashi125]

Unfortunately, I wasn't able to figure out a workaround on a ScrollViewHandler. Instead, I reused XF's ScrollViewRenderer, and manually set the Frame of the ViewForZooming as a workaround. this eliminates the bug where the screen repositions itself off the screen after sleep or button tap.

            var frameSize = new CGSize(this.Width, this.Height);
            var nativeView = ((UIKit.UIView)zoomableSV.Handler.PlatformView);
            nativeView.Subviews[0].Frame = new CGRect(x: 0, y: 0, width: frameSize.Width , height: frameSize.Height);

[Cast324]

Unfortunately, I wasn't able to figure out a workaround on a ScrollViewHandler. Instead, I reused XF's ScrollViewRenderer, and manually set the Frame of the ViewForZooming as a workaround. this eliminates the bug where the screen repositions itself off the screen after sleep or button tap.

            var frameSize = new CGSize(this.Width, this.Height);
            var nativeView = ((UIKit.UIView)zoomableSV.Handler.PlatformView);
            nativeView.Subviews[0].Frame = new CGRect(x: 0, y: 0, width: frameSize.Width , height: frameSize.Height);

We're experiencing this same issue. When were you setting the frame? In the backing class OnSizeAllocated?

[Takashi125]

In our application, I only needed to adjust the native view's frame after adding child views inside the StackLayout contained within the ScrollViewer. This was necessary because rendering a UIScrollView using the ScrollViewRenderer does not automatically set the frame for the ViewForZooming child. It appears that in addition to setting the ViewForZooming, manually adjusting its frame is also required.