WPF 使用UserControl来切换界面

<Window x:Class="WpfApp1.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:WpfApp1"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">

    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="200"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <Border Grid.Column ="0"  BorderThickness="3" BorderBrush="Gray">
            <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="50"/>
                    <RowDefinition Height="50"/>
                </Grid.RowDefinitions>
                <Button Content="用户控件1" Click="ButtonClick1" Margin="3"/><!--使用按键事件来切换-->
                <Button Content="用户控件2" Click="ButtonClick2" Margin="3" Grid.Row="1"/>
            </Grid>
        </Border>

        <Border Grid.Column ="1" BorderBrush="Gray" BorderThickness="3">
            <ContentPresenter  Content="{Binding UserContent}"/><!--使用内容呈现器来显示用户控件界面-->
        </Border>
    </Grid>
</Window>

using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;


namespace WpfApp1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window, INotifyPropertyChanged
    {
        
        private UserControl1 UserControl1 = new UserControl1();//实例化用户控件1
        private UserControl2 UserControl2 = new UserControl2();//实例化用户控件2

        public MainWindow()
        {
            InitializeComponent();
            DataContext = this;
        }

        private void ButtonClick1(object sender, RoutedEventArgs e)
        {
            UserContent = UserControl1;//内容呈现器绑定的UserContent赋值给用户控件1
        }

        private void ButtonClick2(object sender, RoutedEventArgs e)
        {
            UserContent = UserControl2;//内容呈现器绑定的UserContent赋值给用户控件2
        }

        private UserControl _content;
        //内容呈现器绑定到UserContent
        public UserControl UserContent
        {
            get { return _content; }
            set
            {
                _content = value;
                OnPropertyChanged("UserContent");
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        protected virtual void OnPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

<UserControl x:Class="WpfApp1.UserControl1"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:WpfApp1"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="800">
    <StackPanel>
        <Label  Content="用户界面1" HorizontalAlignment="Center"/>
        <Label Name="myLabel" Content="0" HorizontalAlignment="Center"/>
        <Button Content="计数" Click="Button_Click"/>
    </StackPanel>
</UserControl>

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

namespace WpfApp1
{
    /// <summary>
    /// UserControl1.xaml 的交互逻辑
    /// </summary>
    public  partial class UserControl1 : UserControl
    {
        private int i = 0;
        public UserControl1()
        {
            InitializeComponent();
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            i++;
            myLabel.Content = i.ToString();
        }
    }
}