Bind from ControlTemplate to ViewModel

Question

I have stripped down my problem to a minimal example: My DataGrid is defined by a ControlTemplate and in that ControlTemplate I cannot bind to anything from my ViewModel.

This is the simplified ViewModel:

public class ViewModel : PropertyChangedBase
{
    private string text1;

    public ViewModel()
    {
        this.text1 = "tx1!";
    }

    public string Text1
    {
        get { return text1; }
        set
        {
            if (value == text1) return;
            text1 = value;
            NotifyOfPropertyChange(() => Text1);
        }
    }
}

I tried to bind to Text1 with several methods. Most things I find via Google suggest FindAncestor but it did not work either:

<Window x:Class="DataGridTemplateBinding.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:DataGridTemplateBinding"
        Title="MainWindow" Height="350" Width="525"
        x:Name="LayoutRoot"
        >
    <Window.Resources>
        <ControlTemplate x:Key="TableTemplate">
            <DataGrid>
                <DataGrid.Columns>
                    <DataGridTextColumn Header="Column 1" />
                    <!-- by ElementName -->
                    <DataGridTextColumn Header="{Binding DataContext.Text1, ElementName=LayoutRoot}" />
                    <DataGridTextColumn Header="{Binding Text1, ElementName=LayoutRoot}" />

                    <!-- by Ancestor type (Window) -->
                    <DataGridTextColumn Header="{Binding DataContext.Text1, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}" />
                    <DataGridTextColumn Header="{Binding Text1, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}" />

                    <!-- by templated parent -->
                    <DataGridTextColumn Header="{Binding DataContext.Text1, RelativeSource={RelativeSource TemplatedParent}}" />
                    <DataGridTextColumn Header="{Binding Text1, RelativeSource={RelativeSource TemplatedParent}}" />

                    <!-- by self?? -->
                    <DataGridTextColumn Header="{Binding DataContext.Text1, RelativeSource={RelativeSource Self}}" />
                    <DataGridTextColumn Header="{Binding Text1, RelativeSource={RelativeSource Self}}" />

                    <DataGridTextColumn Header="{Binding Content.DataContext.Text1, RelativeSource={RelativeSource TemplatedParent}}" />
                    <DataGridTextColumn Header="{Binding Content.Text1, RelativeSource={RelativeSource TemplatedParent}}" />

                    <DataGridTextColumn Header="{Binding DataContext.Text1}" />
                    <DataGridTextColumn Header="{Binding Text1}" />

                    <DataGridTextColumn Header="Column End" />
                </DataGrid.Columns>
            </DataGrid>
        </ControlTemplate>
    </Window.Resources>
    <Window.DataContext>
        <local:ViewModel />
    </Window.DataContext>
    <Grid>
        <DataGrid Template="{StaticResource TableTemplate}" />
    </Grid>
</Window>

How can a column in the template bind to anything in the ViewModel? I cannot image this would not be possible.

For completeness, these are the errors logged to output. Their order does not correspond with the order of the XAML.

System.Windows.Data Error: 40 : BindingExpression path error: 'DataContext' property not found on 'object' ''DataGridTextColumn' (HashCode=28365320)'. BindingExpression:Path=DataContext.Text1; DataItem='DataGridTextColumn' (HashCode=28365320); target element is 'DataGridTextColumn' (HashCode=28365320); target property is 'Header' (type 'Object')

System.Windows.Data Error: 40 : BindingExpression path error: 'Text1' property not found on 'object' ''DataGridTextColumn' (HashCode=54811268)'. BindingExpression:Path=Text1; DataItem='DataGridTextColumn' (HashCode=54811268); target element is 'DataGridTextColumn' (HashCode=54811268); target property is 'Header' (type 'Object')

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=DataContext.Text1; DataItem=null; target element is 'DataGridTextColumn' (HashCode=55195297); target property is 'Header' (type 'Object')

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=Text1; DataItem=null; target element is 'DataGridTextColumn' (HashCode=38845522); target property is 'Header' (type 'Object')

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Window', AncestorLevel='1''. BindingExpression:Path=DataContext.Text1; DataItem=null; target element is 'DataGridTextColumn' (HashCode=2399386); target property is 'Header' (type 'Object')

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Window', AncestorLevel='1''. BindingExpression:Path=Text1; DataItem=null; target element is 'DataGridTextColumn' (HashCode=31265986); target property is 'Header' (type 'Object')

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=DataContext.Text1; DataItem=null; target element is 'DataGridTextColumn' (HashCode=6837024); target property is 'Header' (type 'Object')

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=Text1; DataItem=null; target element is 'DataGridTextColumn' (HashCode=17422861); target property is 'Header' (type 'Object')

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=Content.DataContext.Text1; DataItem=null; target element is 'DataGridTextColumn' (HashCode=32669489); target property is 'Header' (type 'Object')

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=Content.Text1; DataItem=null; target element is 'DataGridTextColumn' (HashCode=22361045); target property is 'Header' (type 'Object')

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=DataContext.Text1; DataItem=null; target element is 'DataGridTextColumn' (HashCode=7953856); target property is 'Header' (type 'Object')

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=Text1; DataItem=null; target element is 'DataGridTextColumn' (HashCode=65911433); target property is 'Header' (type 'Object')

A simple {Binding Text1} should do it. Are you setting the DataContext from anywhere else? — Mike Eason
So your DataGrid has in it's template another DataGrid ? — Novitchi S
@MikeEason Unfortunately a simple {Binding Text1} does not do the trick. DataContext is only set for the Window. App.xaml & co. are standard, this is nearly all the code in the minimal example project. — ZoolWay
@NovitchiS The template for the DataGrid is coming from a ResourceDictionary in the full-blown application. But even this minimalistic XAML does not work. — ZoolWay

Anand Murali Anand Murali · Accepted Answer · 2015-11-13T15:12:17

Set the HeaderTemplate for DataGridTextColumn as shown below

<DataGridTextColumn  >
    <DataGridTextColumn.HeaderTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}, Path=DataContext.Text1}"></TextBlock>
        </DataTemplate>
    </DataGridTextColumn.HeaderTemplate>
</DataGridTextColumn>

Bind from ControlTemplate to ViewModel

2 Answers