Testdem/TestForDemo/MainWindow.xaml

<Window x:Class="TestForDemo.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:TestForDemo"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="100"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>

        <Frame x:Name="MainFrame" NavigationUIVisibility="Hidden" Grid.Row="1"/>
    </Grid>
</Window>