<Window x:Class="LayoutPanels.SharedSizeGroup"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="SharedSizeGroup" Height="321.6" Width="380.8"
    >
  
    <Grid Grid.IsSharedSizeScope="True" Margin="3">
      <Grid.RowDefinitions>
        <RowDefinition></RowDefinition>
        <RowDefinition Height="Auto"></RowDefinition>
        <RowDefinition></RowDefinition>
      </Grid.RowDefinitions>

      <Grid Grid.Row="0" Margin="3" Background="LightYellow" ShowGridLines="True">
        <Grid.ColumnDefinitions>
          <ColumnDefinition Width="Auto" SharedSizeGroup="TextLabel"></ColumnDefinition>
          <ColumnDefinition Width="Auto"></ColumnDefinition>
          <ColumnDefinition></ColumnDefinition>
        </Grid.ColumnDefinitions>

        <Label Margin="5">A very long bit of text</Label>
       <!-- <GridSplitter Grid.Column="1" VerticalAlignment="Stretch" HorizontalAlignment="Center" Width="10"></GridSplitter> -->
        <Label Grid.Column="1" Margin="5">More text</Label>
        <TextBox Grid.Column="2" Margin="5">A text box</TextBox>
      </Grid>
      <Label Grid.Row="1" >Some text in between the two grids...</Label>
      <Grid Grid.Row="2" Margin="3" Background="LightYellow"  ShowGridLines="True">
        <Grid.ColumnDefinitions>
          <ColumnDefinition Width="Auto" SharedSizeGroup="TextLabel"></ColumnDefinition>
          <ColumnDefinition></ColumnDefinition>
        </Grid.ColumnDefinitions>

        <Label Margin="5">Short</Label>
        <TextBox Grid.Column="1" Margin="5">A text box</TextBox>
      </Grid>
    </Grid>
</Window>
