我如何设置我的UWP页面在启动时具有恒定的宽度和高度？

<Page
    x:Class="YourNamespace.YourPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Width="800"
    Height="600">
    <!-- 页面内容 -->
</Page>

<Page
    x:Class="YourNamespace.YourPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
        </Grid.ColumnDefinitions>
        <!-- 页面内容 -->
    </Grid>
</Page>

public YourPage()
{
    InitializeComponent();
    Loaded += YourPage_Loaded;
}

private void YourPage_Loaded(object sender, RoutedEventArgs e)
{
    // 设置宽度和高度
    Width = 800;
    Height = 600;
}