#1,040 – An Example of Dependency Property Inheritance

One of the attributes of dependency properties in WPF is that they support inheritance of property values within a tree of user interface elements.  Controls (dependency objects) within the tree that make use of a particular dependency property can set a property value locally or retrieve a value from an element higher up in the tree.  The local value takes precedence over the inherited value and then in turn applies to all elements “further down”.

(There are a number of other places from which a dependency property can get its value).

Below is an example.  FontSize is set to 20 for the top-level Window.  This value is use for lower-level elements unless they set their own value.  The GroupBox sets FontSize to 14, which then applies to it and elements under it.  Within the GroupBox, the second Label sets its own value for FontSize.

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:sys="clr-namespace:System;assembly=mscorlib"
        xmlns:local="clr-namespace:WpfApplication1"
        Title="Dependency Properties" 
        Width="280" Height="252"
        FontSize="20">

    <StackPanel Name="spOuter" 
                Margin="5">
        <Label Name="lbl1" Content="Label 1"/>
        <Label Name="lbl2" Content="Label 2"/>
        <GroupBox Name="gb1" Header="Stuff" FontSize="14">
            <StackPanel Name="spInner" Orientation="Horizontal">
                <Label Name="lbl3" Content="Label 3"/>
                <Label Name="lbl4" Content="Label 4" FontSize="10"/>
            </StackPanel>
        </GroupBox>
        <Button Name="btn1" Content="I'm a Button"
                            Padding="10,5" HorizontalAlignment="Center"
                            Click="btn1_Click"/>
    </StackPanel>
</Window>

See this post for another example of dependency property inheritance.