[Mac] TitleBar not always initally set

[tj-devel709]

Description of Change

When the TitleBar on MacCatalyst is set, on the initial page, it would not always display properly. The size and color would show up, but the page would not shift its content below the TitleBar and no elements would show inside the TitleBar. In a simple shell page, this behavior was not observed. However, it was observed inside a NavigationPage. In the NavigationPage example, if I pushed another ContentPage with the TitleBar set there, the titleBar would then display correctly.

The issue lied in the SetUpTitleBar method in the WindowViewController.cs file when comparing if (newTitleBar != iTitleBar). In the NavigationPage scenario, the initial window.TitleBar?.ToPlatform(mauiContext); was not null. Then when the MapTitleBar called SetUpTitleBar again, there would be a second comparison of two different types which would then null out our original TitleBar and remove the handler. When the handler was removed, everything would be reset leading to our elements in the titlebar not being displayed and the window content not shifting.

Issues Fixed

Fixes #27413

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Comments suppressed due to low confidence (4)

src/Core/src/Platform/iOS/WindowViewController.cs:111

• [nitpick] The variable name 'newTitleBar' is ambiguous. It should be renamed to 'titleBar'.

var newTitleBar = window.TitleBar;

src/Core/src/Platform/iOS/WindowViewController.cs:112

• [nitpick] The variable name 'newPlatTitleBar' is ambiguous. It should be renamed to 'platformTitleBar'.

var newPlatTitleBar = newTitleBar?.ToPlatform(mauiContext);

src/Core/src/Platform/iOS/WindowViewController.cs:110

• Ensure that the behavior change is covered by tests in TestCases.HostApp and TestCases.Shared.Tests.

public void SetUpTitleBar(IWindow window, IMauiContext mauiContext)

src/Core/src/Platform/iOS/WindowViewController.cs:110

• Verify that the public documentation reflects the behavior change if it affects the public API.

public void SetUpTitleBar(IWindow window, IMauiContext mauiContext)

[PureWeen]

/rebase