如何在VisualTreeHelper.GetParent（）更改时将属性附加到控件或使用会更新的绑定？

Question

I have a Button for which I need to detect if it goes into the ToolBarOverflowPanel.

Current Code:

(Logic: Monitor Children.Count for AncestorType ToolBarPanel , send to converter and if the value( ToolBarPanel.Children.Count ) = FallbackValue then ToolBarPanel probably didn't register as an Ancestor since the Button is now in ToolBarOverflowPanel instead)

public class IsInOverflowPanel : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value?.ToString().Equals("-1");
    }
    /*ConvertBack(...) not included here*/
}

and XAML:

<ControlTemplate.Resources>
    <local:IsInOverflowPanel x:Key="MyOverflowDetector"/>
</ControlTemplate.Resources>

<ControlTemplate.Triggers>
    <DataTrigger Binding="{Binding Children.Count, Converter={StaticResource MyOverflowDetector}, RelativeSource={RelativeSource AncestorType=ToolBarPanel}, FallbackValue=-1}" Value="True">
        <!--Do Stuff Here-->
    </DataTrigger>
</ControlTemplate.Triggers>

The problem with this code is that it doesn't update when the button goes into the ToolBarOverflowPanel .

But it works at first. My conclusion is that Children.Count isn't giving update notifications. Is there a way to fix it?

How can I force the converter to update? What kind of binding do I need to make it happen?

Answer 1

Try this for the binding:

<ControlTemplate.Resources>
    <local:IsOverflowPanelConverter x:Key="IsOverflowPanel" />
</ControlTemplate.Resources>
<ControlTemplate.Triggers>
    <DataTrigger Binding="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ToolBarOverflowPanel}}, Converter={StaticResource IsOverflowPanel}}" Value="True">

    </DataTrigger>
</ControlTemplate.Triggers>

and this converter

public class IsOverflowPanelConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value?.GetType() == typeof(ToolBarOverflowPanel);
    }

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

I haven't tested it, so let me know if there are any problems.