xamarin/Xamarin.Forms

UWP Missing back button after PushModalAsync

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#6,107 opened on May 6, 2019

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Description

Description

After a modal window in UWP is closed, the back button and page title are not shown after toggling between tabs on a Tab Page. This is not a problem in iOS or Android. This is not a problem if the same page is shown using PushAsync.

Suspect line 457 of Xamarin.Forms.Platform.UWP.NavigationPageRenderer should reference Navigation.NavigationStack.Count rather than PageController.InternalChildren.Count

Steps to Reproduce

  1. Run the attached program
  2. Click step 1 button to add a member to the navigation stack
  3. Click on Tab 2
  4. Click on Tab 1
  5. Click on Test 2 - Show page via PushModalAsync
  6. Close by clicking on button or press the back button in the top left corner

Expected Behavior

The back button and page title should be visible

Actual Behavior

The back button is not present. The page title show be visible (there is space so the navigation bar is still present)

Basic Information

  • Version with issue: 3.4.0.1008975
  • Last known good version: unknown
  • IDE: Visual Studio 2017 15.9.11
  • Platform Target Frameworks:
    • UWP: 16299
  • Nuget Packages: NETStandard.Library 2.0.3 Xamarin.Forms 3.4.0
  • Affected Devices:

Screenshots

before step 4

after step 4

Reproduction Link

BackButtonMissing.UWP.zip

Contributor guide

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.
half day
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# basicsXamarin.Forms navigationUWP platform
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
The issue suggests line 457 of Xamarin.Forms.Platform.UWP.NavigationPageRenderer should use Navigation.NavigationStack.Count instead of PageController.InternalChildren.Count. Investigate the NavigationPageRenderer code to confirm the correct property and implement the fix. Ensure the back button appears after modal navigation and tab switching.