GridSplitterの簡単な例

<Window x:Class="Layout.MainWindow"

        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

        Title="MainWindow" Height="350" Width="525">

    <Grid>

        <Grid>

            <Grid.RowDefinitions>

                <RowDefinition Height="25"></RowDefinition>

                <RowDefinition></RowDefinition>

            </Grid.RowDefinitions>

            <Grid.ColumnDefinitions>

                <ColumnDefinition Width="150"></ColumnDefinition>

                <ColumnDefinition Width="auto"></ColumnDefinition>

                <ColumnDefinition></ColumnDefinition>

            </Grid.ColumnDefinitions>

            <TextBox Grid.ColumnSpan="3" BorderBrush="Black"></TextBox>

            <TextBox Grid.Row="1" BorderBrush="Black"></TextBox>

            <GridSplitter Grid.Row="1" Grid.Column="1"

                          VerticalAlignment="Stretch"

                          HorizontalAlignment="Center"

                          Width="5"

                          Background="Gray"

                          ShowsPreview="True"></GridSplitter>

            <TextBox Grid.Row="1" Grid.Column="2" BorderBrush="Black"></TextBox>

        </Grid>

    </Grid>

</Window>