xamarin/Xamarin.Forms

HasUnevenRows fires ItemAppearing for invisible screen items when the cell is an Image

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#3,874 opened on Sep 22, 2018

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a/listviewe/5 :clock5:help wantedinactivep/Androidt/bug :bug:up-for-grabs

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Description

Description

If a ListView has cells that are made up of only Image instances (or wrapper layouts whose only content is an Image) and HasUnevenRows is set to true, then ItemAppearing will be fired for virtually every list item even if it does not appear on the screen. This is bad for scenarios involving infinite scrolling. The issue seems to exist on both Android and iOS.

Ref: an old issue (27845) that's been resolved.

Steps to Reproduce

  1. Run the attached repro
  2. Observe that ItemAppearing is fired for dozens of items even though it should be fired only a few times upon page load

Reproduction Link

App2.zip

Contributor guide

Research direction
Reproduce the issue by running the attached app. Investigate the ListView's measure and layout logic for HasUnevenRows, particularly when cells contain only images. Look for where ItemAppearing is fired and why it fires for off screen items.
Tech stack
csharp
Domain
frontend
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.
Stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
csharp
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70