[Bug] CollectionView ScrollTo Position Is off when Collectionview has a header

[rileemallon]

Description

Steps to Reproduce

1. fork the collectionview sample
2. add collectionview header
3. call collectionView.ScrollTo

Expected Behavior

When scrolling to item with scroll position center, the item should be vertically centered within the collectionview area

Actual Behavior

As you increase the height of the header (Can be easily tested by increasing the padding of a label and the vertical centered of the item is no longer centered.

<CollectionView.Header>
   <StackLayout> 
       <Label Text="header" Padding="10,70"></Label>
   </StackLayout>
</CollectionView.Header> 

Basic Information

• Version with issue: 4.7
• Last known good version: unknown
• IDE: rider/visual studio for mac
• Platform Target Frameworks:
  • iOS: 11.1
• Nuget Packages:
• Affected Devices: iOS simulator

Screenshots

Reproduction Link

https://github.com/xamarin/xamarin-forms-samples/tree/master/UserInterface/CollectionViewDemos

https://docs.microsoft.com/en-us/xamarin/xamarin-forms/user-interface/collectionview/scrolling

Workaround

unknown

[LelicKAS]

I have the same problem ....
CollectionView.ScrollTo incorrectly determines any position if the list has a Header and Footer .... Invalid position for any of Start, Center and End ....
Any updates on this issue?

[quentinR0bert]

I have the same issue on iOS and Android with Xamarin Forms 4.8

[fbmiranda7]

I can confirm that this bug is reproducible on our project.