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[Windows] Fix "PlatformView cannot be null here" Exception using VisualStates #27877

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[Windows] Fix "PlatformView cannot be null here" Exception using VisualStates #27877

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jsuarezruiz
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Description of Change

Fix "PlatformView cannot be null here" Exception using VisualStates on Windows.

System.InvalidOperationException: PlatformView cannot be null here
   at Microsoft.Maui.Handlers.ViewHandler`2.get_PlatformView()
   at Microsoft.Maui.Handlers.ButtonHandler.MapBackground(IButtonHandler handler, IButton button)
   at Microsoft.Maui.Controls.VisualElement.MapBackgroundColor(IViewHandler handler, IView view)
   at Microsoft.Maui.Controls.Element.OnBindablePropertySet(BindableProperty property, Object original, Object value, Boolean changed, Boolean willFirePropertyChanged)
   at Microsoft.Maui.Controls.BindableObject.SetValueActual(BindableProperty property, BindablePropertyContext context, Object value, Boolean currentlyApplying, SetValueFlags attributes, SetterSpecificity specificity, Boolean silent)
   at Microsoft.Maui.Controls.BindableObject.SetValueCore(BindableProperty property, Object value, SetValueFlags attributes, SetValuePrivateFlags privateAttributes, SetterSpecificity specificity)
   at Microsoft.Maui.Controls.Setter.Apply(BindableObject target, SetterSpecificity specificity)
   at Microsoft.Maui.Controls.VisualStateManager.GoToState(VisualElement visualElement, String name)
   at Microsoft.Maui.Controls.VisualElement.ChangeVisualState()
   at Microsoft.Maui.Controls.View.ChangeVisualState()
   at Microsoft.Maui.Controls.Button.ChangeVisualState()
   at Microsoft.Maui.Controls.VisualElement.OnIsFocusedPropertyChanged(BindableObject bindable, Object oldvalue, Object newvalue)
   at Microsoft.Maui.Controls.Element.OnBindablePropertySet(BindableProperty property, Object original, Object value, Boolean changed, Boolean willFirePropertyChanged)
   at Microsoft.Maui.Controls.BindableObject.SetValueActual(BindableProperty property, BindablePropertyContext context, Object value, Boolean currentlyApplying, SetValueFlags attributes, SetterSpecificity specificity, Boolean silent)
   at Microsoft.Maui.Controls.BindableObject.SetValueCore(BindableProperty property, Object value, SetValueFlags attributes, SetValuePrivateFlags privateAttributes, SetterSpecificity specificity)
   at Microsoft.Maui.Controls.BindableObject.SetValue(BindablePropertyKey propertyKey, Object value, SetterSpecificity specificity)
   at Microsoft.Maui.Controls.VisualElement.Microsoft.Maui.IView.set_IsFocused(Boolean value)
   at Microsoft.Maui.Handlers.ViewHandler.UpdateIsFocused(Boolean isFocused)
   at Microsoft.Maui.Handlers.ViewHandler.DisconnectingHandler(FrameworkElement platformView)
   at Microsoft.Maui.Handlers.ViewHandler.OnDisconnectHandler(Object platformView)
   at Microsoft.Maui.Handlers.ElementHandler.DisconnectHandler(Object platformView)
   at Microsoft.Maui.Handlers.ElementHandler.Microsoft.Maui.IElementHandler.DisconnectHandler()
   at Microsoft.Maui.ViewExtensions.DisconnectHandlers(IView view)
   at Microsoft.Maui.Controls.Page.SendNavigatedFrom(NavigatedFromEventArgs args, Boolean disconnectHandlers)
   at Microsoft.Maui.Controls.NavigationPage.SendNavigated(Page previousPage, NavigationType navigationType)
   at Microsoft.Maui.Controls.NavigationPage.MauiNavigationImpl.<>c__DisplayClass8_0.<OnPopToRootAsync>b__2()

In the added sample, we have two pages, each with a Button to navigate forward and backward. Each Button is styled using VisualStates. After navigating back, ChangeVisualState is invoked which will invoke ButtonHandler.MapBackground. However, the button is null at this point, the handler has been disconnected.
The PR include changes to check if the PlatformView is not null and loaded before invoke the ChangeVisualState method.

Issues Fixed

Fixes #27101

@jsuarezruiz jsuarezruiz added t/bug Something isn't working area-xaml XAML, CSS, Triggers, Behaviors platform/windows labels Feb 18, 2025
@Copilot Copilot AI review requested due to automatic review settings February 18, 2025 12:32
@jsuarezruiz jsuarezruiz requested a review from a team as a code owner February 18, 2025 12:32
Copilot
Copilot AI reviewed Feb 18, 2025
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Copilot reviewed 4 out of 6 changed files in this pull request and generated no comments.

Files not reviewed (2)
  • src/Controls/tests/TestCases.HostApp/Issues/Issue27101.xaml: Language not supported
  • src/Controls/tests/TestCases.HostApp/Issues/Issue27101SecondPage.xaml: Language not supported
Comments suppressed due to low confidence (1)

src/Controls/tests/TestCases.HostApp/Issues/Issue27101SecondPage.xaml.cs:10

  • The OnNavigateBackButtonClicked method is not covered by tests. Add a test case to ensure this method works as expected.
async void OnNavigateBackButtonClicked(object sender, EventArgs e)

@jsuarezruiz
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/rebase

jfversluis
jfversluis requested changes Feb 27, 2025
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Looks like this one has some relevant test failures?

@michelmoorlag
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I am kind of waiting for this fix. Would be nice if we can get this pr merged so it will be in the next version?

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/rebase

MartyIX
MartyIX reviewed May 30, 2025
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src/Controls/src/Core/VisualElement/VisualElement.cs
IsFocused ? VisualStateManager.CommonStates.Focused : VisualStateManager.CommonStates.Unfocused);
}
}
catch(ObjectDisposedException)
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Suggested change
catch(ObjectDisposedException)
catch (ObjectDisposedException)

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I wonder about this approach. The PR description mentions:

In the added sample, we have two pages, each with a Button to navigate forward and backward. Each Button is styled using VisualStates. After navigating back, ChangeVisualState is invoked which will invoke ButtonHandler.MapBackground. However, the button is null at this point, the handler has been disconnected.

So why is ChangeVisualState called when the handler was disconnected?

MartyIX
MartyIX reviewed May 30, 2025
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src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue27101.cs
using UITest.Appium;
using UITest.Core;

namespace Microsoft.Maui.TestCases.Tests.Issues
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super nit: can be file-scoped namespace

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MartyIX commented May 30, 2025

@jsuarezruiz

The PR include changes to check if the PlatformView is not null and loaded before invoke the ChangeVisualState method.

This does not appear to be true. This PR adds a try-catch or not?

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@MartyIX MartyIX MartyIX left review comments

Copilot code review Copilot Copilot left review comments

@jfversluis jfversluis jfversluis requested changes

@StephaneDelcroix StephaneDelcroix Awaiting requested review from StephaneDelcroix StephaneDelcroix is a code owner automatically assigned from dotnet/dotnet-maui-reviewers

@tj-devel709 tj-devel709 Awaiting requested review from tj-devel709 tj-devel709 is a code owner automatically assigned from dotnet/dotnet-maui-reviewers

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"PlatformView cannot be null here" Exception in Switch control [Windows]
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