原理比较简单，但是有个坑，为了使界面能够正确更新，记得使用 INotifyPropertyChanged 接口来实现属性更改通知。

<Window x:Class="PageTest.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:PageTest"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="0.1*"/>
<RowDefinition/>
</Grid.RowDefinitions>
<StackPanel Orientation="Horizontal">
<Button Width="50" Height="25" VerticalAlignment="Top" HorizontalAlignment="Left" Margin="5" Click="Button_Click"></Button>
<Button Width="50" Height="25" VerticalAlignment="Top" HorizontalAlignment="Left" Margin="5" Click="Button_Click_1"></Button>
</StackPanel>
<Frame Grid.Row="1" Content="{Binding CurMain}" NavigationUIVisibility="Hidden"></Frame>
</Grid>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
namespace PageTest
{
/// 

/// Interaction logic for MainWindow.xaml
/// 
[AddINotifyPropertyChangedInterface]
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
DataContext = this;
}
object curMain;
public object CurMain { get => curMain; set => curMain = value; }
private void Button_Click(object sender, RoutedEventArgs e)
{
CurMain = new Page1();
}
private void Button_Click_1(object sender, RoutedEventArgs e)
{
CurMain = new Page2();
}
}
}