CODEWITHSUNDEEP
wpfdependency-properties
Padmaja
Padmaja

Reputation: 447

WPF - Binding failing to a User Control Dependency Property

I have a Control Items Group that is bound to an ObservableCollection. The ItemTemplate for each of the items works if it is set to a TextBlock as:

<DataTemplate x:Key="SampleTemplate">
  <TextBlock Text="{Binding FirstName}"/>
</DataTemplate>

I created a User Control with a TextBlock within it. I want to pass the above "FirstName" to the User Control. I am trying to do this by defining a DependencyProperty in the User control code behind as:

public static DependencyProperty SomeValueProperty = DependencyProperty.Register(
  "SomeValue",
  typeof(Object),
  typeof(SampleControl));

public string SomeValue
{
  get
  {
    return (string)GetValue(SomeValueProperty);
  }
  set
  {
    (this.DataContext as UserControlViewModel).Name = value;
    SetValue(SomeValueProperty, value);
  }

and in the MainWindow's ItemTemplate, I changed it to:

<DataTemplate x:Key="SampleTemplate">
  <local:SampleControl SomeValue="{Binding FirstName}"/>
</DataTemplate>

But this does not work. I am not sure why this Binding is failing when the same Binding works fine for a TextBlock within MainWindow. What am I doing wrong here?

Upvotes: 0

Views: 452

Answers (1)

Justin Pihony
Justin Pihony

Reputation: 67065

There is a lot I can see wrong and it could be any of these things breaking this:

public static DependencyProperty SomeValueProperty = DependencyProperty.Register(
  "SomeValue", typeof(String), typeof(SampleControl), 
  new FrameworkPropertyMetaData(new PropertyChangedCallback(OnSomeValueChanged)));

private static void OnSomeValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
  ((d as SampleControl).DataContext as UserControlViewModel).Name = e.NewValue;
}

public string SomeValue
{
  get
  {
    return (string)GetValue(SomeValueProperty);
  }
  set
  {
    SetValue(SomeValueProperty, value);
  } 
}

Notice I am using a String, and not Object. And, doing extra work on changing values in the PropertyChangedCallBack. And, I am only doing the basics in the SomeValue POCO as the real work is done in SetValue. Also of note, I did not do any exception handling, which could be your error also...if set's .Name call fails in your current code, then SetValue never hits

Upvotes: 1

Related Questions