WPF Binding to Child Collection

Question

Hello, if the parent's datasource has a child property that is a collection (let's say it is called ChildCollection) is there a trick to reference it?

So, this code sample is basically what I am attempting to do. But when I use this approach I do not get any data to my child controls.

<UserControl>
    <UserControl.Resources>
        <sample:Data x:Key="MyData" />
    </UserControl.Resources>
    <Canvas DataContext="{StaticResource MyData}">
        <TextBlock Text="{Binding Title}" />
        <My:UserControl DataContext="{Binding ChildCollection}" />
    </Canvas>
</UserControl>

My dependency property looks like this:

public static readonly DependencyProperty DataProperty =
    DependencyProperty.Register("Data", typeof(IEnumerable), typeof(ButtonList), 
    new UIPropertyMetadata(new PropertyChangedCallback(DataChanged)));
public DoubleCollection Data
{
    get { return (DoubleCollection)GetValue(DataProperty); }
    set { SetValue(DataProperty, value); }
}
static void DataChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
    (sender as FrameworkElement).DataContext = e.NewValue;
}
public void SetData(IEnumerable data)
{
    (View as CollectionViewSource).Source = data;
}

Thank you in advance for your help.

Answer 1

If I understand your code right, you want the collection to be in the UserControl's DataProperty.

To achieve this, you have to do the Binding like this:

 <Canvas DataContext="{StaticResource MyData}">
    <TextBlock Text="{Binding Title}" />
    <My:UserControl Data="{Binding ChildCollection}" />
 </Canvas>

Instead of:

<Canvas DataContext="{StaticResource MyData}">
    <TextBlock Text="{Binding Title}" />
    <My:UserControl DataContext="{Binding ChildCollection}" />
 </Canvas>

Hope this is helpful. Also: I dont know if a canvas inherits it's DataContext to childs. Use a Panel instead (Grid/Stackpanel/WrapPanel).

Jan

Answer 2

Below is a working sample with a user control (ButtonList) that has a DP of type IEnumerable<double> and creates a button for each double value. Compare it to you code to see what you are doing incorrectly.

XAML:

<UserControl x:Class="UserControlDemo.ButtonList"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:UserControlDemo="clr-namespace:UserControlDemo"
    Name="_buttonList">
    <ItemsControl ItemsSource="{Binding Path=Data, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControlDemo:ButtonList}}}">
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <Button Content="{Binding}" />
            </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ItemsControl>
</UserControl>

Code behind:

using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;

namespace UserControlDemo
{
    public partial class ButtonList : UserControl
    {
        public ButtonList()
        {
            InitializeComponent();
        }

        public IEnumerable<double> Data
        {
            get { return (IEnumerable<double>)GetValue(DataProperty); }
            set { SetValue(DataProperty, value); }
        }

        public static readonly DependencyProperty DataProperty =
            DependencyProperty.Register("Data",
                                        typeof(IEnumerable<double>), 
                                        typeof(ButtonList), 
                                        new UIPropertyMetadata(new List<double>()));
    }
}

Usage:

 <UserControlDemo:ButtonList Data="{Binding Path=Numbers}" />