Improve performance and stability of BindableLayout

[albyrock87]

Description of Change

This PR improves the performance of BindableLayout in all cases where the item source changes entirely or there is a Reset or Replace event (see more on #23135).
The strategy is simple: reuse existing views when possible, and simply change the BindingContext.

Video - Before

Video - After

Issues Fixed

Fixes #23135

[davidortinau]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[PureWeen]

/rebase

[PureWeen]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[MartyIX]

https://github.com/dotnet/maui/pull/23136/checks?check_run_id=28884287267 mentions a test failure that might be a real change in behavior:

Microsoft.Maui.TestCases.Tests.Issues.Issue22417(Windows).AddItemsToCarouselViewWorks

VisualTestUtils.VisualTestFailedException :
Snapshot different than baseline: AddItemsToCarouselViewWorks.png (20.50% difference)
If the correct baseline has changed (this isn't a a bug), then update the baseline image.
See test attachment or download the build artifacts to get the new snapshot file.

More info: https://aka.ms/visual-test-workflow

[albyrock87]

@MartyIX thanks for point it out, there was indeed an issue which I fixed in 997079d but it was related to another failing test.

The one you're talking about seems to be a different issue given that Carousel test is not using a BindableLayout.

[PureWeen]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[MartyIX]

Now I can see this test to fail:

BindableLayout Does Not Leak
Assert.Equal() Failure: Values differ\r\nExpected: 6\r\nActual:   3

Not sure if it is a real issue but looks like it can.

[albyrock87]

Thanks @MartyIX for keeping an eye on this.
The test had to be updated to account for the enhanced behavior: baa4aa2
No real memory leaks fortunately ;)

[PureWeen]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[albyrock87]

Faling unrelated tests:

• Core.UnitTests (Android) UnitTests.NavigationPageLifecycleTests.RemoveInnerPage(true)
• Controls.TestCases.Shared.Tests (Android): RegisterTwoDoubleTapHandlersAndCheckNumberOfFiredEventsAsync
• Controls.DeviceTests (iOS): HandlerDoesNotLeak(typeof(WebView))

[MartyIX]

Tests appear to be green now.

[PureWeen]

/rebase

[PureWeen]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[cagriy]

I see a change in the BindableLayout behaviour 8.0.90, which may or may not be related to this, but I wanted to report it:
I update BindableLayout using

BindableLayout.SetItemsSource(MyStackLayout, MyListOfObjects);

Before the update, the layout was redrawn and reapplied the settings (in my case colors) that were hardcoded in XAML, after the update, the content gets updated, but the changes to layout items (such as colors) persist.

I managed to resolve the issue by adding a

MyStackLayout.Children.Clear();

before setting the item source. I just wanted to report it in case it was an unintentional breaking change.

[albyrock87]

@cagriy you're correct, this was an intentional breaking change, and your workaround is correct.

BindableLayout is now trying to reuse the views as much as possible considering that creating a platform view from scratch has higher cost than changing a few binded property.

One thing you could do instead of the Clear to benefit from this change is override OnBindingContextChanged in your custom view and reset the colors there when BindingContext is not null.

[cagriy]

@albyrock87 , that's fantastic, and thanks for the quick reply, would it be a good idea to move this change into the breaking changes section so that others won't need to troubleshoot the same issue?