I want to make a custom GridSplitter that combines a regular splitter behaviour plus a feature – when the splitter resizes automatically one of the areas to zero.

So normal usage is:

<Grid>
  <Grid.ColumnDefinitions>
    <ColumnDefinition Width="0.5*" Name="A"/>
    <ColumnDefinition Width="Auto"/>
    <ColumnDefinition Width="0.5*" Name="B"/>
  </Grid.ColumnDefinitions>
  
  <GridSplitter Grid.Column="1"... />

initially – both columns A and B have same size = 50% of available width.
User can drag the splitter to change their widths.
Now I want user to be able to double click on the splitter (or any other way to initiate the action) – and the column A resized to 0 and B to 100%, if acted again – then A to 100% and B to 0.

Obviously I can do it in the parent by setting column widths in code behind. But I want to reuse this functionality in other parts and make it as simple to use as possible.