将 DataGridColumns Header 绑定到窗口的 DataContext

Question

I have a DataGrid and want to bind the Header -property to a property of my windows DataContext but I did not get it working.

Binding can be such a pain as (for me) it is never clear which context this has when simply using Binding . I know that the "Context" in the Binding={} is a single element of the DataGrid s ItemsSource . But what is the "Context" for Header={Binding ???} ?

I've already tried:

Header="{Binding Path=DataContext.MyProperty, RelativeSource={RelativeSource Self}}
Header="{Binding Path=DataContext.MyProperty, RelativeSource={RelativeSource TemplatedParent}}
Header="{Binding Path=DataContext.MyProperty, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type MyWindow}}}
Header="{Binding Path=DataContext.MyProperty, ElementName=MyWindowName}

I tried with and without Path but nothing is working.

For example, using the last one with ElementName I get the following binding-exception:

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=DataContext.MyProperty; DataItem=null; target element is 'DataGridTextColumn' (HashCode=51072575); target property is 'Header' (type 'Object')

Is there any tool to check/change bindings at runtime? Or even to know what the current "Context" is?

Note: The DataGrid is inside a Mahapps.Flyout (not sure if this has something to say).

Answer 1

Since DataGridTextColumn or any other supported data grid columns are not part of visual tree of datagrid so they don't inherit the DataContext of datagrid . Since, they don't lie in visual tree so any try to get DataContext using RelativeSource won't work.

Solution - You can create a proxy element to bind the data context of window/control ; use that proxy element to bind the Header of DataGridTextColumn .

<Grid>
   <Grid.Resources>
       <FrameworkElement x:Key="ProxyElement" DataContext="{Binding}"/>
   </Grid.Resources>
       <ContentControl Visibility="Collapsed" Content="{StaticResource ProxyElement}"></ContentControl>
       <DataGrid  
                       ItemsSource="{Binding Collection}" 
                       AutoGenerateColumns="False">
          <DataGrid.Columns>
              <DataGridTextColumn Header="{Binding DataContext.MyProperty, Source={StaticResource ProxyElement}}" Binding="{Binding PropertyName}" />
          </DataGrid.Columns>
     </DataGrid>
</Grid>