xamarin/Xamarin.Forms

[iOS] DataTemplateSelector doesn't work when an item is re-created in code-behind

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#7,836 opened on Oct 5, 2019

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a/collectionviewhelp wantedp/iOS 🍎t/bug :bug:up-for-grabs

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Description

Description

This works in ListView but not CollectionView. When a template selector is used (in this case with two different data templates) and a button click clears StackLayout children and adds a new view, CollectionView renders items in wrong positions.

Steps to Reproduce

  1. Run repro.
  2. Scroll to item 49.
  3. Click the "Clear" button
  4. Observe that the scroll position changes and there are multiple items with the new "Cleared at timestamp" view.
  5. Comment out Items.Add(new Model1())
  6. Re-run the test.
  7. Observe that the issue does not happen this time.

Expected Behavior

Code-behind changes should not confuse the CollectionView when a DataTemplateSelector is used.

Basic Information

  • Version with issue: 4.4.0.1211-nightly
  • Last known good version: N/A
  • IDE: VS2019
  • Affected Devices: XS

Screenshots

file (1)

Reproduction Link

App100.zip

Contributor guide

Research direction
Investigate how CollectionView handles item re creation with DataTemplateSelector, focusing on the Clear and re add logic. Check if the issue relates to view caching or template resolution order.
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.
2
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
Git
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75