TextBox/RichEditBox Shouldn't Force Light Theme on Focus

Describe the bug Both TextBox and RichEditText include a visual state like this:

<VisualState x:Name="Focused">
    <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentElement" Storyboard.TargetProperty="RequestedTheme">
        <DiscreteObjectKeyFrame KeyTime="0" Value="Light" />
    </ObjectAnimationUsingKeyFrames>
</VisualState>

This interferes with lightweight styling, most notably when trying to theme the editor to remain dark in a dark theme.

Steps to reproduce the bug

1. New UWP Application
2. Use this XAML for the main page (modify the x:Class to match your project)

<Page x:Class="App6.MainPage"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"
      RequestedTheme="Dark">

    <Grid>
        <Grid.Resources>
            <SolidColorBrush x:Key="TextControlBackground" Color="Transparent" />
            <SolidColorBrush x:Key="TextControlBackgroundPointerOver" Color="Transparent" />
            <SolidColorBrush x:Key="TextControlBackgroundFocused" Color="{ThemeResource SystemAltHighColor}" />
            <SolidColorBrush x:Key="TextControlForegoundFocused" Color="{ThemeResource SystemBaseHighColor}" />
        </Grid.Resources>
        
        <TextBox Text="Here is some text that I want to edit in a dark editor" FontSize="30"
                 TextWrapping="Wrap" />
    </Grid>
</Page>

Expected behavior I expect the TextBox to use SystemBaseHighColor from the dark theme, but it resolves to the Light theme instead. Even worse, TextControlBackgroundFocused resolves to dark because its theme isn’t changed in the Style.

Screenshots Screenshot showing the dark text (with some text selected in order to show that text exists)

[lukeblevins]

I think by default, user input controls like TextBox should not force light theme when dark mode is enabled. In many apps, it looks jarring and quite inconsistent for this control to light up white when focus is invoked.

[chingucoding]

@chingucoding , would you mind creating some prototype gif where this is done over image?

Sure!