how to bind fontsize for wpf textbox?

Question

I have a textbox control that works appropriately, without binding, while its font size should be changed dynamically.

I wanted to do it right and work using binding.

I tried to bind the FontSize using (xaml):

<UserControl x:Class="<ClassName>"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         mc:Ignorable="d" Focusable="True"
         d:DesignHeight="300" d:DesignWidth="300">
<Grid>
    <TextBox x:Name="_textBox" Visibility="Visible" xml:space="preserve"
             Background="{Binding RelativeSource={RelativeSource FindAncestor,AncestorType={x:Type UserControl}},Path=Background}"
             Foreground="{Binding RelativeSource={RelativeSource FindAncestor,AncestorType={x:Type UserControl}},Path=Foreground}"
             FontFamily="{Binding RelativeSource={RelativeSource FindAncestor,AncestorType={x:Type UserControl}},Path=FontFamily}"
             BorderBrush="{Binding RelativeSource={RelativeSource FindAncestor,AncestorType={x:Type UserControl}},Path=BorderBrush}"
             Text="{Binding MultilineText}"
             FontSize="{Binding Path=MultilineFontSize}"
             KeyUp="_textBox_KeyUp"
             PreviewTextInput="_textBox_PreviewTextInput"
             DataObject.Pasting="_textBox_Pasting"
             VerticalContentAlignment="Top"
             PreviewKeyDown="TextBox_OnPreviewKeyDown"
             TextWrapping="Wrap"
             ScrollViewer.VerticalScrollBarVisibility="Visible"
             />
</Grid>

and in the code behind:

private double _multilineFontSize;
public double MultilineFontSize
    {
        get { return GetBestFittingFontSize();  }
        set
        {
            if (value != _multilineFontSize)
            {
                _multilineFontSize = value;
                OnPropertyChanged("MultilineFontSize");
            }
        }
    }

The only use for _multilineFontSize is to replace _textbox.Text wherever I used it (in events etc).

GetBestFittingFontSize() is a function (that works appropriately) and calculates the font size I need to use. Take it as given. It returns double.

It doesn't work. Does any one have any idea why? (maybe some DataContext issues?)

Answer 1

You can try to use the ViewBox which can be used to scale its content.

<Viewbox StretchDirection="Both" Stretch="Uniform">
    <local:UserControl1 Height="100" Width="100"/>
</Viewbox>