How to Write a DependencyProperty for a TextBlock when it is a child element of a parent Button class in WPF C#?

Question

Hi there, I want to make a Dependency Property for a Text Block and the functionality of this property is to apply a Scale Transformation on the Text Block but I am unable to do that Because it's a child element inside of a Button class. I have a reference Dependency Property where the Same Logic (Scale Transformation) is applied on a Grid because the Grid is the Root Element but the Data Binding would not work or fails and completely breakdown when the UI Element is inside of an another parent Element rather than the Root element.

Here is the Working Code of the Dependency Property (When UI Element (Grid) is the Root Element) :

public partial class MainWindow : Window
{
    public MainWindow() => InitializeComponent();
    #region ScaleValue Depdency Property
    public static readonly DependencyProperty ScaleValueProperty = DependencyProperty.Register("ScaleValue", typeof(double), typeof(MainWindow), new UIPropertyMetadata(1.0, new PropertyChangedCallback(OnScaleValueChanged), new CoerceValueCallback(OnCoerceScaleValue)));
    private static object OnCoerceScaleValue(DependencyObject o, object value)
    {
        MainWindow mainWindow = o as MainWindow;
        if (mainWindow != null)
            return mainWindow.OnCoerceScaleValue((double)value);
        else return value;
    }
    private static void OnScaleValueChanged(DependencyObject o, DependencyPropertyChangedEventArgs e)
    {
        MainWindow mainWindow = o as MainWindow;
        if (mainWindow != null)
            mainWindow.OnScaleValueChanged((double)e.OldValue, (double)e.NewValue);
    }
    protected virtual double OnCoerceScaleValue(double value)
    {
        if (double.IsNaN(value))
            return 1.0f;
        value = Math.Max(0.1, value);
        return value;
    }
    protected virtual void OnScaleValueChanged(double oldValue, double newValue) { }
    public double ScaleValue
    {            
        get => (double)GetValue(ScaleValueProperty);
        set => SetValue(ScaleValueProperty, value);
    }
    #endregion
    private void MainGrid_SizeChanged(object sender, EventArgs e) => CalculateScale();
    private void CalculateScale()
    {
        double yScale = ActualHeight / 250f;
        double xScale = ActualWidth / 200f;
        double value  = Math.Min(xScale, yScale);
        ScaleValue = (double)OnCoerceScaleValue(myMainWindow, value);
    }
}

And here How I applied it on the Main Grid (Root Element) :

<Window x:Class="WpfApplication1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" 
    Name="myMainWindow"
    Width="200" Height="250">
<Grid Name="MainGrid" SizeChanged="MainGrid_SizeChanged">
    <Grid.LayoutTransform>
        <ScaleTransform x:Name="ApplicationScaleTransform"
                        CenterX="0"
                        CenterY="0"
                        ScaleX="{Binding ElementName=myMainWindow, Path=ScaleValue}"
                        ScaleY="{Binding ElementName=myMainWindow, Path=ScaleValue}" />
    </Grid.LayoutTransform>
    <Grid VerticalAlignment="Center" HorizontalAlignment="Center" Height="150">
        <TextBlock FontSize="20" Text="Hello World" Margin="5" VerticalAlignment="Top" HorizontalAlignment="Center"/>
        <Button Content="Button" VerticalAlignment="Bottom" HorizontalAlignment="Center"/>
    </Grid>
</Grid>

All of the above Code works really great but the ScaleX and ScaleY Binding fails When I tried to apply on the Below TextBlock Code :

<Button
     x:Name="BtnSettings"
     Width="70"
     Height="24"
     Margin="165,14,0,0"
     HorizontalAlignment="Left"
     VerticalAlignment="Top"
     DockPanel.Dock="Left"
     FontSize="10"
     RenderOptions.BitmapScalingMode="NearestNeighbor"
     RenderOptions.ClearTypeHint="Enabled"
     SnapsToDevicePixels="True"
     UseLayoutRounding="True">
     <Button.Content>
         <TextBlock
             x:Name="myTextbox"
             Margin="0,-2,0,0"
             FontSize="10"
             RenderOptions.BitmapScalingMode="NearestNeighbor"
             RenderOptions.ClearTypeHint="Enabled"
             SnapsToDevicePixels="True"
             TextAlignment="Center"
             TextOptions.TextFormattingMode="Display"
             TextOptions.TextRenderingMode="ClearType"
             TextWrapping="Wrap"           
             UseLayoutRounding="True">
             Settings
             <TextBlock.RenderTransform>
                 <ScaleTransform       
                                x:Name="ApplicationScaleTransform"                        
                                CenterX="0"
                                CenterY="0"                                
                                ScaleX="{Binding ElementName=myMainWindow, Path=ScaleValue}"
                                ScaleY="{Binding ElementName=myMainWindow, Path=ScaleValue}" />
             
                </TextBlock.RenderTransform>
         </TextBlock>
     </Button.Content>
 </Button>

As you clearly see from the Above Code that the TextBlock is present inside of the Button Element and thus the Binding will fail. My Question is How Can I write a DependencyProperty for a TextBlock So that I can achieve the Scale transformation on it.

Another important part is, if I can achieve this thing by using any custom class or any attach behavior, that answer is also welcome.

Answer 1

@MERUN KUMAR MAITY, Welcome to Microsoft Q&A, you could try the following code to scale the textblock inside the button with MainWindow.

First, please create two custom Converter classes.

    public class WidthToScaleConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            double width = (double)value;
            
            return width / 100.0;
        }
        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }
    public class HeightToScaleConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            double height = (double)value;
      
            return height / 50.0;
        }
        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

Second, please add the following xaml code in App.xaml.

  <Application.Resources>
    <local:WidthToScaleConverter x:Key="WidthToScaleConverter"/>
    <local:HeightToScaleConverter x:Key="HeightToScaleConverter"/>
</Application.Resources>

Third, please use the following XAML code to reduce the Text size without effecting Font Size 10.

<Window x:Class="WpfApp1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp1"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800"  Name="myMainWindow">
    <Grid Name="MainGrid" SizeChanged="MainGrid_SizeChanged">
        <Grid.LayoutTransform>
            <ScaleTransform x:Name="ApplicationScaleTransform"
                       CenterX="0"
                       CenterY="0"
                       ScaleX="{Binding ElementName=myMainWindow, Path=ScaleValue}"
                       ScaleY="{Binding ElementName=myMainWindow, Path=ScaleValue}" />
        </Grid.LayoutTransform>
        <Grid VerticalAlignment="Center" HorizontalAlignment="Center" Height="150">
            <Button VerticalAlignment="Center" HorizontalAlignment="Center" Height="80" Width="180">
                <Button.LayoutTransform>
                    <ScaleTransform ScaleX="{Binding ElementName=myMainWindow, Path=ScaleValue}"
                               ScaleY="{Binding ElementName=myMainWindow, Path=ScaleValue}" />
                </Button.LayoutTransform>
                <!-- Embedding TextBlock via Button.Content -->
                <Button.Content>
                    <!-- Binding FontSize to ScaleValue with a multiplier -->
                    <TextBlock x:Name="myTextBlock"
                           Text="Settings"
                           HorizontalAlignment="Center"
                           VerticalAlignment="Center"
                           FontSize="10">
                        <TextBlock.LayoutTransform>
                            <!-- ScaleTransform will change the size of the TextBlock without affecting the font size -->
                            <ScaleTransform ScaleX="{Binding ActualWidth, ElementName=myButton, Converter={StaticResource WidthToScaleConverter}}" 
                                        ScaleY="{Binding ActualHeight, ElementName=myButton, Converter={StaticResource HeightToScaleConverter}}"/>
                        </TextBlock.LayoutTransform>
                    </TextBlock>
                </Button.Content>
            </Button>
        </Grid>
    </Grid>
</Window>

Note: I used the same code with you in MainWindow.cs.

Tested Result:

As you can see from the above picture, fontsize will be changed by the window size.

Hope it could help you.

Best Regards,

Jack

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