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WPF: binding to ObservableCollection in ControlTemplate is not updated

I created ControlTemplatefor my custom control MyControl.

MyControlcomes from System.Windows.Controls.Controland defines the following property public ObservableCollection<MyControl> Children{ get; protected set; }.

To display nested child controls, I use ItemsControl( StackPanel) which is surrounded GroupBox. If there are no child controls, I want to hide GroupBox.

Everything works fine when the application starts. The group field and child controls are displayed if the Children property originally contained at least one element. In another case, it is hidden.

The problem begins when the user adds a child control to an empty collection. Visibility GroupBoxstill collapsed. The same problem occurs when the last child control is removed from the collection. GroupBoxstill displayed. Another symptom is that the transducer is HideEmptyEnumerationConverternot triggered. Adding / removing child controls for non-empty collections works as expected.

What happened to the next binding? Obviously, it works once, but does not update, although the collection that I am linking is of type ObservableCollection.

<!-- Converter for hiding empty enumerations -->
<Common:HideEmptyEnumerationConverter x:Key="hideEmptyEnumerationConverter"/>
<!--- ... --->

<ControlTemplate TargetType="{x:Type MyControl}">
  <!-- ... other stuff that works ... -->
  <!-- Child components -->
  <GroupBox Header="Children"
            Visibility="{Binding RelativeSource={RelativeSource TemplatedParent},
              Path=Children, Converter={StaticResource hideEmptyEnumerationConverter}}">
    <ItemsControl ItemsSource="{TemplateBinding Children}"/>
  </GroupBox>
</ControlTemplate>

.

[ValueConversion(typeof (IEnumerable), typeof (Visibility))]
public class HideEmptyEnumerationConverter : IValueConverter
{
    #region IValueConverter Members

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        int itemCount = ((IEnumerable) value).Cast<object>().Count();
        return itemCount == 0 ? Visibility.Collapsed : Visibility.Visible;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }

    #endregion
}

Another, more general question: how do you guys debug your bindings? Found this ( http://bea.stollnitz.com/blog/?p=52 ), but still it’s very difficult for me to do this.

I am happy for any help or suggestion.

+1
2

, Children , . , . , Count . - DataTrigger :

<ControlTemplate TargetType="{x:Type MyControl}">
  <!-- ... other stuff that works ... -->
  <!-- Child components -->
  <GroupBox x:Name="gb" Header="Children">
    <ItemsControl ItemsSource="{TemplateBinding Children}"/>
  </GroupBox>
  <ControlTemplate.Triggers>
      <DataTrigger Binding="{Binding Path=Children.Count, RelativeSource={RelativeSource TemplatedParent}}"
                   Value="0">
        <Setter TargetName="gb" Property="Visibility" Value="Collapsed" />
      </DataTrigger>
  </ControlTemplate.Triggers>
</ControlTemplate>
+6

, . , INotifyPropertyChanged, Collection Collection Collection PropertyChanged.

:

public class MyControl : Control, INotifyPropertyChanged
{
    static MyControl()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(MyControl), new FrameworkPropertyMetadata(typeof(MyControl)));
    }

    public ObservableCollection<UIElement> Children
    {
        get { return (ObservableCollection<UIElement>)GetValue(ChildrenProperty); }
        set { SetValue(ChildrenProperty, value); }
    }

    // Using a DependencyProperty as the backing store for Children.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty ChildrenProperty =
        DependencyProperty.Register("Children", typeof(ObservableCollection<UIElement>), typeof(MyControl), new UIPropertyMetadata(0));

    public MyControl()
    {
        Children = new ObservableCollection<UIElement>();
        Children.CollectionChanged += new System.Collections.Specialized.NotifyCollectionChangedEventHandler(Children_CollectionChanged);
    }

    void Children_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
        RaisePropertyChanged("Children");
    }

    public event PropertyChangedEventHandler PropertyChanged;
    public void RaisePropertyChanged(String propertyName)
    {
        PropertyChangedEventHandler temp = PropertyChanged;
        if (temp != null)
        {
            temp(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}
0

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