Code
using System.Windows;

namespace BookStore
{
    public interface IContent
    {
        UIElement Content { get; set; }
    }
}

Code
<UserControl x:Class="BookStore.Test"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    Width="600" Height="400">
    <Grid x:Name="LayoutRoot" Background="White" >
        <StackPanel Orientation="Vertical" HorizontalAlignment="Center" Margin="50" Background="AliceBlue" Width="200" Height="100">
            <TextBlock TextAlignment="Center">
                这是Test.Xaml文件
            </TextBlock>
            <Button Height="25" Width="150" Content="转到Test2.xaml" Click="Button_Click"></Button>
        </StackPanel>
       
    </Grid>
</UserControl>

Code
using System.Windows;
using System.Windows.Controls;

namespace BookStore
{

//手动增加, IContent ，让Test实现IContent接口
    public partial class Test : UserControl, IContent 
    {
        public Test()
        {
            InitializeComponent();
        }

private void Button_Click(object sender, RoutedEventArgs e)
        {
            //实现切换(点击test.xaml上的按钮将切换到Test2"场景")
            (Application.Current.RootVisual as IContent).Content = new Test2();                       
        }

/// <summary>
        /// 增加一个Content属性
        /// </summary>
        public new UIElement Content
        {
            get
            {
                return base.Content;
            }
            set
            {
                base.Content = value;
            }
        }

}
}

Code
<UserControl x:Class="BookStore.Test2"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    Width="600" Height="400">
    <Grid x:Name="LayoutRoot" Background="White" >
        <StackPanel Orientation="Vertical" HorizontalAlignment="Center" Margin="50" Background="Beige"  Width="200" Height="100">
            <TextBlock TextAlignment="Center">
                这是Test2.Xaml文件
            </TextBlock>
            <Button Height="25" Width="150" Content="转到Test.xaml" Click="Button_Click"></Button>
        </StackPanel>

</Grid>
</UserControl>

Code
using System.Windows;
using System.Windows.Controls;

namespace BookStore
{
    //手动增加, IContent ，让Test2实现IContent接口
    public partial class Test2 : UserControl, IContent
    {
        public Test2()
        {
            InitializeComponent();
        }

private void Button_Click(object sender, RoutedEventArgs e)
        {
        //就这一行有点一不样(点击test2.xaml上的按钮将还回到Test"场景")
            (Application.Current.RootVisual as IContent).Content = new Test();            
        }

/// <summary>
        /// 增加一个Content属性
        /// </summary>
        public new UIElement Content
        {
            get
            {
                return base.Content;
            }
            set
            {
                base.Content = value;
            }
        } 
    }
}