A converter return a border. It doesn't work.

Question

When the tag of b1 changes, I want to change the child of the b1.

the converter of returnBorder is returning a new border.

 

<Border Name="b1" Tag="HelloWorld">
     <Border.Child>
         <Binding ElementName="b1" Path="Tag" Converter="{StaticResource returnBorder}"></Binding>
     </Border.Child>
 </Border>

Answer 1

Border.Child (or rather Decorator.Child) is not a dependency property, so you can't bind to it.

You can however, use your own attached property, to set the Child property "from within", so to speak.

using System.Windows;
using System.Windows.Controls;

namespace WpfApplication68.Helpers
{
    class Attached
    {
        public static UIElement GetBindableChild(DependencyObject obj)
        {
            return (UIElement)obj.GetValue(BindableChildProperty);
        }

        public static void SetBindableChild(DependencyObject obj, UIElement value)
        {
            obj.SetValue(BindableChildProperty, value);
        }

        public static readonly DependencyProperty BindableChildProperty =
            DependencyProperty.RegisterAttached("BindableChild", typeof(UIElement), typeof(Attached), new UIPropertyMetadata(null, BindableChildPropertyChanged));

        static void BindableChildPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
            var ele = sender as Decorator;
            ele.Child = (UIElement)e.NewValue;
        }
    }
}

using System;
using System.Windows.Data;
using System.Windows.Controls;
using System.Windows.Media;

namespace WpfApplication68.Helpers
{
    public class MyConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            if (value == null) return null;

            var border = new Border { Background = Brushes.Red, Width=100, Height=50 };
            border.Child = new TextBlock { Text = value.ToString() };
            return border;
        }

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

<Window x:Class="WpfApplication68.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525" xmlns:local="clr-namespace:WpfApplication68.Helpers" >
    <Window.Resources>
        <local:MyConverter x:Key="MyConverter"/>
    </Window.Resources>
    <Grid>
        <Border local:Attached.BindableChild="{Binding Tag, RelativeSource={RelativeSource Self}, Converter={StaticResource MyConverter}}" Tag="Hello World" />
    </Grid>
</Window>

 

BTW, I uploaded the demo to MSDN Samples, in case you cannot replicate this from the code snippets above:

Binding to Border Child (aka Decorator Child)

(please rate it if you like it ;)

Regards,
Pete

---

#PEJL