Form materials cannot exist at the same time as the page

[hui3215]

Describe the bug

I use the following method and want to change the material of the form, but here this. Content cannot be null, and null in the framework will show the corresponding page

To Reproduce

using System.Runtime.InteropServices; // For DllImport
using WinRT; // required to support Window.As<ICompositionSupportsSystemBackdrop>()

WindowsSystemDispatcherQueueHelper m_wsdqHelper; // See separate sample below for implementation
Microsoft.UI.Composition.SystemBackdrops.MicaController m_micaController;
Microsoft.UI.Composition.SystemBackdrops.DesktopAcrylicController m_acrylicController;
Microsoft.UI.Composition.SystemBackdrops.SystemBackdropConfiguration m_configurationSource;

bool TrySetAcrylicBackdrop()
{
    if (Microsoft.UI.Composition.SystemBackdrops.DesktopAcrylicController.IsSupported())
    {
        m_wsdqHelper = new WindowsSystemDispatcherQueueHelper();
        m_wsdqHelper.EnsureWindowsSystemDispatcherQueueController();

        // Hooking up the policy object
        m_configurationSource = new Microsoft.UI.Composition.SystemBackdrops.SystemBackdropConfiguration();
        this.Activated += Window_Activated;
        this.Closed += Window_Closed;
        ((FrameworkElement)this.Content).ActualThemeChanged += Window_ThemeChanged;

        // Initial configuration state.
        m_configurationSource.IsInputActive = true;
        SetConfigurationSourceTheme();

        m_acrylicController = new Microsoft.UI.Composition.SystemBackdrops.DesktopAcrylicController();

        // Enable the system backdrop.
        // Note: Be sure to have "using WinRT;" to support the Window.As<...>() call.
        m_acrylicController.AddSystemBackdropTarget(this.As<Microsoft.UI.Composition.ICompositionSupportsSystemBackdrop>());
        m_acrylicController.SetSystemBackdropConfiguration(m_configurationSource);
        return true; // succeeded
    }

    return false; // Acrylic is not supported on this system
}

private void Window_Activated(object sender, WindowActivatedEventArgs args)
{
    m_configurationSource.IsInputActive = args.WindowActivationState != WindowActivationState.Deactivated;
}

private void Window_Closed(object sender, WindowEventArgs args)
{
    // Make sure any Mica/Acrylic controller is disposed so it doesn't try to
    // use this closed window.
    if (m_acrylicController != null)
    {
        m_acrylicController.Dispose();
        m_acrylicController = null;
    }
    this.Activated -= Window_Activated;
    m_configurationSource = null;
}

private void Window_ThemeChanged(FrameworkElement sender, object args)
{
    if (m_configurationSource != null)
    {
        SetConfigurationSourceTheme();
    }
}

private void SetConfigurationSourceTheme()
{
    switch (((FrameworkElement)this.Content).ActualTheme)
    {
        case ElementTheme.Dark:    m_configurationSource.Theme = Microsoft.UI.Composition.SystemBackdrops.SystemBackdropTheme.Dark; break;
        case ElementTheme.Light:   m_configurationSource.Theme = Microsoft.UI.Composition.SystemBackdrops.SystemBackdropTheme.Light; break;
        case ElementTheme.Default: m_configurationSource.Theme = Microsoft.UI.Composition.SystemBackdrops.SystemBackdropTheme.Default; break;
    }
}

 TrySetAcrylicBackdrop();

Page is not displayed

 TrySetAcrylicBackdrop();
this.content = null;

Page displays, but form materials do not

Additional context

No response

Applies to the following platforms:

• [X] WinUI
• [ ] WPF
• [ ] UWP

About your setup

• Visual Studio Version: 2022
• Template Studio Wizard Version: latest
• Windows Build: