GridSplitter
The GridSplitter control is a control that allows a user to resize the space between Grid rows or columns.
<Grid ColumnDefinitions="*, 4, *">
<Rectangle Grid.Column="0" Fill="Blue"/>
<GridSplitter Grid.Column="1" Background="Black" ResizeDirection="Columns"/>
<Rectangle Grid.Column="2" Fill="Red"/>
</Grid>
<Grid RowDefinitions="*, 4, *">
<Rectangle Grid.Row="0" Fill="Blue"/>
<GridSplitter Grid.Row="1" Background="Black" ResizeDirection="Rows"/>
<Rectangle Grid.Row="2" Fill="Red"/>
</Grid>
