WPF Binding to Child Collection - wpf

Question

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}" />