Multicolumntreeview Column Autosize

I am trying to get my columns to autosize to a specific percentage of the controls total width. Do you have any examples of how to do this? I have tried binding the column width to the treeview actual width with a converter but that results in a binding error.

<ms:MulticolumnTreeView DockPanel.Dock="Top" ItemsSource="{Binding Path=BaseFolder.Children}" x:Name="fileTree" HorizontalContentAlignment="Stretch">
            <ms:MulticolumnTreeView.Columns>
                <GridViewColumn Header="Name" Width="{Binding ElementName=fileTree, Path=ActualWidth}"/>

Gives this error:

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=ActualWidth; DataItem=null; target element is 'GridViewColumn' (HashCode=28756230); target property is 'Width' (type 'Double')

Hello Jeremy,

Many apologies for not getting back to you on this -- unfortunately your message fell through the cracks somehow and we didn't pick it up until now.

There's no built-in way to do this.  You'll need to handle the SizeChanged event, or create a derived class and override OnSizeChanged.  To keep the view definition in the XAML, you could create an attached property e.g.

public class ProportionalSizingMulticolumTreeView : MulticolumnTreeView {
    public static double GetWidthProportion(DependencyObject obj) {
      return (double)obj.GetValue(WidthProportionProperty);
    }

    public static void SetWidthProportion(DependencyObject obj, double value) {
      obj.SetValue(WidthProportionProperty, value);
    }

    public static readonly DependencyProperty WidthProportionProperty =
        DependencyProperty.RegisterAttached("WidthProportion", typeof(double),
        typeof(ProportionalSizingMulticolumnTreeView), new UIPropertyMetadata(0.0));

  protected override void OnSizeChanged(EventArgs e) {
    foreach (var column in Columns) {
      double proportion = ProportionalSizingMulticolumnTreeView.GetWidthProportion(column);
      if (proportion != 0) {
        column.Width = ActualWidth * proportion;
      }
    }
  }
}

Then in the XAML:

<local:ProportionalSizingMulticolumnTreeView>
  <local:ProportionalSizingMulticolumnTreeView.Columns>
    <GridViewColumn Header="33.3%" local:ProportionalSizingMulticolumnTreeView.WidthProportion="0.333" />
    <GridViewColumn Header="20%" local:ProportionalSizingMulticolumnTreeView.WidthProportion="0.2" />
    <GridViewColumn Header="Fixed size" />
  </local:ProportionalSizingMulticolumnTreeView.Columns>
</local:ProportionalSizingMulticolumnTreeView>