Binding Dependency Property to View Model - wpf

Question

I have two user controls defined as follows:
User Control 1
XAML
<UserControl x:Class="TestBindings.UserControlOne"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:TestBindings">
<UserControl.DataContext>
<local:UserControlOneViewModel/>
</UserControl.DataContext>
<StackPanel>
<TextBlock Text="{Binding MyProperty}"/>
<local:UserControlTwo PropertyTwo="{Binding DataContext.MyProperty, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}}"/>
</StackPanel>
</UserControl>
Code Behind
public partial class UserControlOne : UserControl
{
public UserControlOne()
{
InitializeComponent();
}
}
User Control 2
XAML
<UserControl x:Class="TestBindings.UserControlTwo"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:TestBindings">
<UserControl.DataContext>
<local:UserControlTwoViewModel/>
</UserControl.DataContext>
<TextBlock Name="TextBlock" Text="{Binding PropertyTwo}"/>
</UserControl>
Code Behind
public partial class UserControlTwo : UserControl
{
public static readonly DependencyProperty PropertyTwoProperty =
DependencyProperty.Register("PropertyTwo", typeof (string), typeof (UserControlTwo),
new FrameworkPropertyMetadata("Default", OnPropertyTwoChanged));
public UserControlTwo()
{
InitializeComponent();
var propertyTwoBinding = new Binding("PropertyTwo") {Mode = BindingMode.TwoWay};
SetBinding(PropertyTwoProperty, propertyTwoBinding);
}
public string PropertyTwo
{
get { return (string) GetValue(PropertyTwoProperty); }
set { SetValue(PropertyTwoProperty, value); }
}
private static void OnPropertyTwoChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var userControlTwo = (UserControlTwo) d;
userControlTwo.PropertyTwo = (string) e.NewValue;
}
}
In UserControlTwo's constructor I bind the dependency property PropertyTwoProperty to a property in the associated ViewModel. I ultimately want to bind this to a property in the ViewModel of UserControlOne, hence UserControlOne xaml
<local:UserControlTwo PropertyTwo="{Binding DataContext.MyProperty, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}}"/>
However this never seems to get set. Any ideas where I may be going wrong?

Answer 1

I think you are trying to pass a property from the datacontext of UserControlOne to a DependencyProperty in UserControlTwo.
In that case you use the below approach and also remove the setbinding in the code in your UserControl2 Constructor. Let me know if this is what you are looking for.
<UserControl x:Class="TestBindings.UserControlOne"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
x:Name="userControl"
xmlns:local="clr-namespace:TestBindings">
<UserControl.DataContext>
<local:UserControlOneViewModel/>
</UserControl.DataContext>
<StackPanel>
<TextBlock Text="{Binding MyProperty}"/>
<local:UserControlTwo PropertyTwo="{Binding DataContext.MyProperty, ElementName=userControl,Mode=TwoWay}"/>
</StackPanel>
</UserControl>