Silverlight UserControl Custom Property Binding

Question

What is the proper way to implement Custom Properties in Silverlight UserControls?

Every \"Page\" in Silverlight is technically a UserControl (they are derived from the

Answer 1

Instead of binding data context to self, you can set the binding in xaml by adding an x:Name for the user control and then binding in the user control xaml follows:

<UserControl
  x:Class="SilverlightCustomUserControl.MyCustomUserControl" 
  x:Name="myUserControl
  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">
    <Grid>
        <StackPanel>
            <TextBox Text="{Binding SelectedText, ElementName=myUserContol, Mode=TwoWay}" />
            <Border BorderBrush="Black" BorderThickness="1">
                <TextBlock Text="{Binding SelectedText,ElementName=myUserControl}" Height="24"></TextBlock>
            </Border>
        </StackPanel>
     </Grid>
</UserControl>

Answer 2

I understand it as the reason your control is not receiving the new value from the maim page is that you are setting the DataContext of the control. If you hadn't then the control's DataContext will be inherited from its parent, the main page in this case.

To get this to work I removed you control's DataContext setting, added an x:Name to each control and set the binding in the constructor of the control using the [name].SetBinding method.

I did the binding in the ctor as I couldn't figure out a way of setting the Source property of the declarative binding in the xaml to Self. i.e. {Binding SelectedText, Mode=TwoWay, Source=[Self here some how]}. I did try using RelativeSource={RelativeSource Self} with no joy.

NOTE: All this is SL3.

Answer 3

The Issue was the UserControl was throwing a DataBinding error (visible in the Output window while debugging)

Because The UserControl's DataContext was set to "Self" in its own xaml, it was looking for the MainPageSelectedText within its own context (it was not looking for the MainPageSelectedText within the "MainPage" which is where you might think it would look, because when you are physically writing/looking at the code that is what is in "context")

I was able to get this "working" by setting the Binding in the code behind. Setting the binding in the code behind is the only way to set the UserControl itself as the "Source" of the binding. But this only works if the Binding is TwoWay. OneWay binding will break this code. A better solution altogether would be to create a Silverlight Control, not a UserControl.

See Also:

http://social.msdn.microsoft.com/Forums/en-US/silverlightcontrols/thread/052a2b67-20fc-4f6a-84db-07c85ceb3303

http://msdn.microsoft.com/en-us/library/cc278064%28VS.95%29.aspx

MyCustomUserControl.xaml

<UserControl
   x:Class="SilverlightCustomUserControl.MyCustomUserControl" 
 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">
 <Grid>
  <StackPanel>
   <TextBox x:Name="UserControlTextBox" />
   <Border BorderBrush="Black" BorderThickness="1">
    <TextBlock x:Name="UserControlTextBlock" Height="24"></TextBlock>
   </Border>
  </StackPanel>
 </Grid>
</UserControl>

MyCustomUserControl.xaml.cs

namespace SilverlightCustomUserControl
{
 public partial class MyCustomUserControl : UserControl
 {

  public string SelectedText
  {
   get { return (string)GetValue(SelectedTextProperty); }
   set { SetValue(SelectedTextProperty, value); }
  }

  public static readonly DependencyProperty SelectedTextProperty =
    DependencyProperty.Register("SelectedText", typeof(string), typeof(MyCustomUserControl), new PropertyMetadata("", SelectedText_PropertyChangedCallback));


  public MyCustomUserControl()
  {
   InitializeComponent();

               //SEE HERE
   UserControlTextBox.SetBinding(TextBox.TextProperty, new Binding() { Source = this, Path = new PropertyPath("SelectedText"), Mode = BindingMode.TwoWay });
   UserControlTextBlock.SetBinding(TextBlock.TextProperty, new Binding() { Source = this, Path = new PropertyPath("SelectedText") });
               //SEE HERE
  }

  private static void SelectedText_PropertyChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e)
  {
   //empty
  }

 }
}