If you change the theme after running the app, it will not be applied normally.

[dimohy]

Description

From a project created with a default project template to App.xaml.cs

	public App()
	{
		InitializeComponent();

		Application.Current.UserAppTheme = AppTheme.Light; // or AppTheme.Dark

		MainPage = new AppShell();
	}

If you specify a theme with UserAppTheme, it seems to work well.

| AppTheme.Dark

| AppTheme.Light

However, if you change 'UserAppTheme' after the app runs, it does not reflect that well.

| Dark

| Change theme to 'Light'

At first, I suspected that 'AppThemeBinding' was missing in 'Styles.xaml' of the control expressed, but this is not the case. (Of course, there were RadioButton and other things that were missing)

1. The background color of the page does not respond to the theme. 'Styles.xaml' specifies the background color of the page as 'AppThemeBinding'.

    <Style ApplyToDerivedTypes="True" TargetType="Page">
        <Setter Property="Padding" Value="0" />
        <Setter Property="BackgroundColor" Value="{AppThemeBinding Light={StaticResource White}, Dark={StaticResource Black}}" />
    </Style>

1. The background color of Shell also does not change depending on the theme. Of course, it depends on the platform, but Android changes and Windows doesn't.

| Android

| Windows Machine

It looks like a bug to me.

Steps to Reproduce

1. Create a MAUI project by selecting MAUI App from the project template
2. Modify 'MainPage.xaml' to change theme by pressing radio button as follows

        <VerticalStackLayout Padding="30" Spacing="25">
            <HorizontalStackLayout
                HorizontalOptions="End"
                IsVisible="true"
                Spacing="8">
                <Label Text="Theme" VerticalTextAlignment="Center" />
                <RadioButton
                    x:Name="lightThemeRadioButton"
                    CheckedChanged="lightThemeRadioButton_CheckedChanged"
                    Content="Light"
                    GroupName="theme"
                    MinimumWidthRequest="80" />
                <RadioButton
                    x:Name="darkThemeRadioButton"
                    CheckedChanged="darkThemeRadioButton_CheckedChanged"
                    Content="Dark"
                    GroupName="theme"
                    MinimumWidthRequest="80" />
            </HorizontalStackLayout>
            ...

3. Modify 'MainPage.xaml.cs' as follows

...
	public MainPage()
	{
		InitializeComponent();

		var theme = Application.Current.RequestedTheme;
		if (theme is AppTheme.Light)
			lightThemeRadioButton.IsChecked = true;
		else if (theme is AppTheme.Dark)
			darkThemeRadioButton.IsChecked = true;
	}

	private void lightThemeRadioButton_CheckedChanged(object sender, CheckedChangedEventArgs e)
	{
		Application.Current.UserAppTheme = AppTheme.Light;
	}

	private void darkThemeRadioButton_CheckedChanged(object sender, CheckedChangedEventArgs e)
	{
		Application.Current.UserAppTheme = AppTheme.Dark;
	}
...

4. Press the Theme RadioButton Light or Dark to see if it is working

Version with bug

Release Candidate 2 (current)

Last version that worked well

Unknown/Other

Affected platforms

Android, Windows

Affected platform versions

Android 21.0, Windows 10.0.17763.0

Did you find any workaround?

No response

Relevant log output

No response

[v-longmin]

Verified repro on 17.3.0 Preview 1.0 [32427.505.main]. Repro with above code.

[dimohy]

.NET MAUI RC3 seems to have solved the problem.

However, when the theme is specified when the app is started, it is not reflected in Windows.

Reproduction is as follows.

public partial class App : Application
{
	public App()
	{
		InitializeComponent();

        Application.Current.UserAppTheme = AppTheme.Light;

        MainPage = new AppShell();
	}
}

Android works fine.

[samhouts]

Duplicate of #6596