xamarin/Xamarin.Forms

[Bug] iOS CollectionView's Scrolled event can not be fired when scrolling in HeaderTemplate

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#8,548 opened on Nov 18, 2019

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Description

Description

I use scrolled event of collection view for detecting scroll offset, then hide the StackLayout when scrolling up for more space at bottom. But when I create a HeaderTemplate which has HeightRequest bigger than current screen's height, the Scrolled event can not be fired, so I can not scroll down for showing the hidden layout. The ItemsViewScrolledEventArgs.VerticalOffset can not be back to zero. Take a look at before and after screenshot

Basic Information

  • Version with issue: Xamarin.Forms 4.3.0.947036
  • iOS: 13.2
  • Nuget Packages:

Screenshots

Before scrolling up image

After, can not scroll down to view the top layout

image

Reproduction link

https://drive.google.com/file/d/1Ug5Hzr2tw947UyDU6SZjqUOdTcMqdFrs/view?usp=sharing

Contributor guide

Research direction
Investigate the iOS native UICollectionView scroll event handling when a large header template is used. Check if the Scrolled event is suppressed due to content offset interaction with the header.
Tech stack
csharp
Domain
mobile
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C#Xamarin.FormsiOS development
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40