xamarin/Xamarin.Forms

Retain Strategy on Listview with DataTemplateSelector causes BindingContext to revert to null

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#3,602 opened on Aug 17, 2018

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Description

Description

The issue seems to come up because of this await

https://github.com/xamarin/Xamarin.Forms/blob/a9a7277ad8d6b40a9f28081c248ba282a6476d95/Xamarin.Forms.Core/TemplatedItemsList.cs#L1206

The await happens, a new template is swapped in, and then the above code sets the BindingContext back to null. If you set the ListView Cache strategy to Recycle the issue doesn't happen because that await doesn't occur

For example I had to do this little hack here

https://github.com/xamarin/Xamarin.Forms/pull/3518/files#diff-bb6d28847711cc5f78841d28a70d000bR168

To make sure the BindingContext doesn't get reset back to null after already being set inside the DataTemplateSelector

Steps to Reproduce

In the Control Gallery remove the hack I added above and you'll see the effect of the BindingContext getting set and then unset to null because of the race condition

Expected Behavior

The BindingContext on the view cell should remain what I set it to. A pending operation shouldn't set it back to null.

Actual Behavior

A pending operation sets the BindingContext back to null

Basic Information

  • Version with issue: 3.2
  • Last known good version: Not sure

Contributor guide

Research direction
Investigate the await in TemplatedItemsList.cs line 1206 that causes BindingContext to revert to null. Examine the race condition with DataTemplateSelector and the workaround in commit 3518.
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.
Stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Mostly clear
Prerequisites
C#Xamarin.Forms
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30