WPF DataTemplate and Binding

Question

I continue my understanding of MVVC with the code of MSDN and I have a question.

In the .xaml they have a list of commands displayed to the screen.

   <Border 
    Grid.Column="0" 
    Style="{StaticResource MainBorderStyle}"
    Width="170"
    >
    <HeaderedContentControl
      Content="{Binding Path=Commands}"
      ContentTemplate="{StaticResource CommandsTemplate}"
      Header="Control Panel"
      Style="{StaticResource MainHCCStyle}"
      />
  </Border>

From here, I understand that the DataContext is set (not shown here) and it will display the collection of Commands. What I do not understand is the CommandsTemplate that you can see below:

<DataTemplate x:Key="CommandsTemplate">
<ItemsControl IsTabStop="False" ItemsSource="{Binding}" Margin="6,2">
  <ItemsControl.ItemTemplate>
    <DataTemplate>
      <TextBlock Margin="2,6">pou
        <Hyperlink Command="{Binding Path=Command}">
          <TextBlock Text="{Binding Path=DisplayName}" />
        </Hyperlink>
      </TextBlock>
    </DataTemplate>
  </ItemsControl.ItemTemplate>
</ItemsControl>
</DataTemplate>

How does the binding is created? How this code tell to check the property Command and DisplayName from the object inside the collection? Is it from the ItemsSource? If yes, I do not understand why it's only at {Binding}. Anyone can explain me please how the DataTemplate binding work from a ContentTemplate?

Answer 1

Example:

XAML

<Window x:Class="WpfApplication2.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300" Loaded="Window_Loaded">
    <Window.Resources>
        <DataTemplate x:Key="CommandsTemplate">
            <ItemsControl IsTabStop="False" ItemsSource="{Binding}" Margin="6,2">
                <ItemsControl.ItemTemplate>
                    <DataTemplate>
                        <TextBlock Margin="2,6">pou
                            <Hyperlink Command="{Binding Path=Command}">
                                <TextBlock Text="{Binding Path=DisplayName}" />
                            </Hyperlink>
                        </TextBlock>
                    </DataTemplate>
                </ItemsControl.ItemTemplate>
            </ItemsControl>
        </DataTemplate>
    </Window.Resources>
    <Grid>
        <Border Width="170">
            <HeaderedContentControl
                Content="{Binding Path=Commands}"
                ContentTemplate="{StaticResource CommandsTemplate}"
                Header="Control Panel"/>
        </Border>
    </Grid>
</Window>

C#

/// <summary>
/// Interaction logic for Window1.xaml
/// </summary>
public partial class Window1 : Window {
    public Window1() {
        InitializeComponent();

        Commands.Add(new Commander() { DisplayName = "DN1" });
        Commands.Add(new Commander() { DisplayName = "DN2" });
        Commands.Add(new Commander() { DisplayName = "DN3" });

        this.DataContext = this;
    }

    private void Window_Loaded(object sender, RoutedEventArgs e) {

    }

    private ObservableCollection<Commander> commands = new ObservableCollection<Commander>();

    public ObservableCollection<Commander> Commands {
        get { return commands; }
        set { commands = value; }
    }
}

public class Commander {
    public ICommand Command { get; set; }
    public string DisplayName { get; set; }
}

Answer 2

The ItemsSource binding to {Binding} binds directly to the DataContext of the ItemsControl (which will look up the chain until it finds a set DataContext). In this case it has been set in the HeaderedContentControl

Each item inside the ItemsControl will then have its DataContext set to an element in the list.

The <ItemsControl.ItemTemplate> is setting the template for each Item inside the list, not for the ItemsControl itself. So that {Binding Path=Command} and {Binding Path=DisplayName} will look at those properties on the elements inside the list.