如何在wpf主窗口中更改页面？

<Grid>
    <Frame x:Name="mainFrame" NavigationUIVisibility="Hidden" />
</Grid>

// 在代码中设置Frame的Source属性
mainFrame.Source = new Uri("Page1.xaml", UriKind.Relative);

<Grid>
    <local:Page1 x:Name="page1" Visibility="Visible" />
    <local:Page2 x:Name="page2" Visibility="Collapsed" />
</Grid>

// 在代码中更改UserControl的可见性
page1.Visibility = Visibility.Collapsed;
page2.Visibility = Visibility.Visible;

<NavigationWindow x:Class="WpfApp.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <Frame x:Name="mainFrame" NavigationUIVisibility="Hidden" />
</NavigationWindow>

// 在代码中进行页面导航
mainFrame.NavigationService.Navigate(new Page1());