How to bind a WPF control to the code behind? - wpf

Question

I have this XAML:
<Window x:Class="WpfBindToCodeBehind.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300"
Loaded="Window_Loaded">
<StackPanel Orientation="Vertical">
<Button Name="ToggleExpand" Click="ToggleExpand_Click">Toggle Expander</Button>
<Expander Name="Expander"
Header="Don't click me, click the button!"
IsExpanded="{Binding RelativeSource={RelativeSource Self},Path=MayExpand}">
<TextBlock Text="{Binding}"/>
</Expander>
</StackPanel>
</Window>
This is the code behind:
public partial class Window1 : Window,INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public Window1()
{
InitializeComponent();
}
private void ToggleExpand_Click(object sender, RoutedEventArgs e)
{
MayExpand = !mayExpand;
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
Expander.DataContext = "Show me";
}
private bool mayExpand;
public bool MayExpand
{
get { return mayExpand; }
set
{
mayExpand = value;
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs("MayExpand"));
}
}
}
The Binding expression for the IsExpanded property is not working. This code is a simplification, in reality the expander's binding is already set through the datacontent of a parent control.
How can I bind the IsExpanded property to a property of the code behind?
Can I bind it to the result of a method in the code behind?

Answer 1

The source for the binding is a RelativeSource.Self. That means the source is the Expander rather than the Window. Something like this will work:
IsExpanded="{Binding MayExpand, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}"
You could also use a name to simplify things:
<Window x:Name="_root">
<Expander IsExpanded="{Binding MayExpand, ElementName=_root}"/>