wrappanelsample.xaml

<Window x:Class="wpf_test.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:wpf_test"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <WrapPanel>
        <Grid
            Background="Gray"
            Margin="5"
            VerticalAlignment="Stretch">
            <Grid
                Height="100"
                Width="100"/>
        </Grid>
        <Grid
            Background="Gray"
            Margin="5"
            VerticalAlignment="Stretch">
            <Grid
                Height="100"
                Width="100"/>
        </Grid>
        <Grid
            Background="Gray"
            Margin="5"
            VerticalAlignment="Stretch">
            <Grid
                Height="100"
                Width="100"/>
        </Grid>
        <Grid
            Background="Gray"
            Margin="5"
            VerticalAlignment="Stretch">
            <Grid
                Height="100"
                Width="100"/>
        </Grid>
        <Grid
            Background="Red"
            Margin="5"
            VerticalAlignment="Stretch">
            <Grid
                Height="50"
                Width="100"/>
        </Grid>
        <Grid
            Background="Red"
            Margin="5"
            VerticalAlignment="Stretch">
            <Grid
                Height="50"
                Width="100"/>
        </Grid>
        <Grid
            Background="Red"
            Margin="5"
            VerticalAlignment="Stretch">
            <Grid
                Height="50"
                Width="100"/>
        </Grid>
        <Grid
            Background="Red"
            Margin="5"
            VerticalAlignment="Stretch">
            <Grid
                Height="50"
                Width="100"/>
        </Grid>
    </WrapPanel>
</Window>