MainView.xaml

<UserControl x:Class="WpfWindowTest.MainView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:WpfWindowTest"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="800">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="*"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"/>
            <ColumnDefinition Width="*"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>

        <Border Grid.Row="0" Grid.Column="0" Background="#aaa"/>
        <Border Grid.Row="0" Grid.Column="1" Background="#ccc"/>
        <Border Grid.Row="0" Grid.Column="2" Background="#aaa"/>

        <Border Grid.Row="1" Grid.Column="0" Background="#ccc"/>
        <Border Grid.Row="1" Grid.Column="1" Background="#aaa"/>
        <Border Grid.Row="1" Grid.Column="2" Background="#ccc"/>

        <Border Grid.Row="2" Grid.Column="0" Background="#aaa"/>
        <Border Grid.Row="2" Grid.Column="1" Background="#ccc"/>
        <Border Grid.Row="2" Grid.Column="2" Background="#aaa"/>
    </Grid>
</UserControl>