WPF Expander - when GridSplitter used to manually resize row, row does not properly collapse

Question

This is what I have

   <Grid.RowDefinitions>
      <RowDefinition Height="Auto" MinHeight="25"/>
      <RowDefinition Height="Auto"/>
      <RowDefinition />
  </Grid.RowDefinitions>

<Expander IsExpanded="False" Grid.Row="0" >
     <DataGrid name="FirstGrid" />
</Expander>
<GridSplitter Grid.Row="1" HorizontalAlignment="Stretch"  Height="5" />
<DataGrid Grid.Row="2" name="SecondGrid" />

When I click the expand button on the expander it correctly expands row 0 to the size of the DataGrid FirstGrid and it properly collapses the row as well. This does not work however if I expand the FirstGrid then manually resize that row by dragging the GridSplitter up or down and then pressing collapse button on the expander. What happens is that FirstGrid collapses but the row itself the FirstGrid is in does not. Any suggestions?

Thanks

Amit Raz Amit Raz · Accepted Answer · 2015-01-22T18:20:17

Rob is right, once you move the gridsplitter, the Height of the first Row will not be Auto anymore, so it will not respond to the change in the expander size In order for this to work you would need to add a behavior to the expander which will listen to the expander.expanded and collapsed event and update the grid row to be auto again. something like this:

public class GridColumnWidthReseterBehaviour : Behavior<Expander>
{
    private Grid _parentGrid;
    public int TargetGridRowIndex { get; set; }
    protected override void OnAttached()
    {
        AssociatedObject.Expanded += AssociatedObject_Expanded;
        AssociatedObject.Collapsed += AssociatedObject_Collapsed;
        FindParentGrid();
    }

    private void FindParentGrid()
    {
        DependencyObject parent = LogicalTreeHelper.GetParent(AssociatedObject);
        while (parent != null)
        {
            if (parent is Grid)
            {
                _parentGrid = parent as Grid;
                return;
            }
            parent = LogicalTreeHelper.GetParent(AssociatedObject);
        }
    }

    void AssociatedObject_Collapsed(object sender, System.Windows.RoutedEventArgs e)
    {
        _parentGrid.RowDefinitions[TargetGridRowIndex].Height= GridLength.Auto;
    }

    void AssociatedObject_Expanded(object sender, System.Windows.RoutedEventArgs e)
    {
        _parentGrid.RowDefinitions[TargetGridRowIndex].Height= GridLength.Auto;
    }
}

And you use it like this:

 <Expander ...>
    <interactivity:Interaction.Behaviors>
                <behaviors:GridColumnWidthReseterBehaviour TargetGridRowIndex="0"></behaviors:GridColumnWidthReseterBehaviour>
            </interactivity:Interaction.Behaviors>

...

WPF Expander - when GridSplitter used to manually resize row, row does not properly collapse

2 Answers