使用MVVM模式进行WPF开发，数据绑定问题
问题如下：
我将MainViewModel设置成MainWindow的DataContext,这个时候修改用户名代表的TextBox,此时不会调用MainViewModel.cs中的

set
            {
                
                if (userinfo == value)
                {
                    return;
                }
                userinfo = value;
                RaisePropertyChanged("UserInfo");
            }

，而是调用

public class User
    {
        public int Id { get; set; }

        public string Name { get; set; }

        public string Password { get; set; }
    }

中的Set方法，但是为什么会通知界面进行更新呢？
User.cs并没有实现INotifiPropertyChange接口，而且也不会调用MainViewModel.cs中的Set方法。
希望各位大神指导下，为什么只调用了User.cs的set方法，却也通知了界面进行更新？



MainWindow.xaml

<TextBlock Grid.Column="0" Grid.Row="0" Text="用户名："></TextBlock>
        <TextBox Grid.Column="1" Grid.Row="0">
            <TextBox.Text>
                <Binding Path="UserInfo.Name" UpdateSourceTrigger="PropertyChanged"  Mode="TwoWay">
                <Binding.ValidationRules>
                    <!--<ExceptionValidationRule />-->
                    <local:UserValidate ValidateType="UserName" ></local:UserValidate>
                </Binding.ValidationRules> 
 
            </Binding>
            </TextBox.Text>
        </TextBox>

MainViewModel.cs

private User userinfo;

        /// <summary>
        /// Sets and gets the UserInfo property.
        /// Changes to that property's value raise the PropertyChanged event. 
        /// </summary>
        public User UserInfo
        {
            get
            {
                return userinfo;
            }

            set
            {
                
                if (userinfo == value)
                {
                    return;
                }
                userinfo = value;
                RaisePropertyChanged("UserInfo");
            }
        }

User.cs

public class User
    {
        public int Id { get; set; }

        public string Name { get; set; }

        public string Password { get; set; }
    }

[解决办法]

    <StackPanel>
        <TextBox   Width="70"  Text="{Binding Path=Userinfo.Name,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}"/>
        <TextBox  Width="70" Text="{Binding Path=Userinfo.Name,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}"/>
        
    </StackPanel>

后台代码

 public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            this.DataContext = new VM();
        }

    }

    public class VM : INotifyPropertyChanged
    {
        private User userinfo;

        /// <summary>
        /// Sets and gets the UserInfo property.
        /// Changes to that property's value raise the PropertyChanged event. 
        /// </summary>
        public User UserInfo
        {
            get
            {
                return userinfo;
            }

            set
            {

                if (userinfo == value) 
 
                {
                    return;
                }
                userinfo = value;
                PropertyChanged(this, new PropertyChangedEventArgs("UserInfo"));
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
    }

    public class User
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Password { get; set; }
    }

另外一个没有更新.....
同学 你是不是代码写错了