WPF How must I set the DataContext

Question

I have a Control inherited from a Listbox. The XAML looks like this:

<ListBox x:Class="Bibliothek.myDockControl"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         mc:Ignorable="d" 
         d:DesignHeight="300" d:DesignWidth="300"
         x:Name="myListBox"
         >
<ListBox.ItemContainerStyle>
    <Style TargetType="ListBoxItem">
        <Setter Property="Height" Value="{Binding ItemHeight, UpdateSourceTrigger=PropertyChanged}"/>
        <Setter Property="Template">           
            <Setter.Value>
                <ControlTemplate TargetType="ListBoxItem">
                    <Border BorderThickness="1" BorderBrush="Black" CornerRadius="2">
                        <DockPanel>
                            <StackPanel DockPanel.Dock="Top" Background="LightGray">
                                <DockPanel Margin="2,2,2,2">
                                    <TextBlock x:Name="Beschreibung" DockPanel.Dock="Left" VerticalAlignment="Center" FontWeight="Bold" Text="{Binding Header,UpdateSourceTrigger=PropertyChanged}"></TextBlock>
                                </DockPanel>
                            </StackPanel>
                            <ContentPresenter DockPanel.Dock="Top" Content="{Binding Content}"></ContentPresenter>
                        </DockPanel>
                    </Border>                                          
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ListBox.ItemContainerStyle>

I have a binding for the Textblock and for the contentpresenter. these bindings are from my own type DockItem. Looks like this:

public class DockItem
{
    public string Header { get; set; }
    public object Content { get; set; }
}

these property for the binding is set in the window where i tested the control and is from typ observablecollection which is binded to the itemsource of the listbox.

when i added a binding for the Height property like above(ItemHeight) that is declared in the code behind i don't know how to set the datacontext. If I set the datacontext in the codebehind of the listbox control like this: DataContext = this; then the bindings for the Header and Content doesnt work.

icebat icebat · Accepted Answer · 2013-02-27T13:34:41

You`re trying to set two different data contexts to one ListBoxItem. If you definitely want to take ItemHeight from parent Window, then you can make it like this:

 <Setter Property="Height" Value="{Binding ItemHeight, RelativeSource={RelativeSource FindAncestor, AncestorType=Window}}"/>

Don`t forget to implement preperty changed notification though, or it won`t react to changes. Alternatively you can add ItemHeight to DockItem class, then your current approach will work ok.

WPF How must I set the DataContext

1 Answers