The INotifyPropertyChanged interface is often used to implement data binding in WPF. Here is a case of INotifyPropertyChanged.

Define a Person class as follows:

1. using System;  
2. using System.Collections.Generic;  
3. using System.Linq;  
4. using System.Text;  
5. using System.ComponentModel;  
6.   
7. namespace WpfApp  
8. {  
9.     public class Person:INotifyPropertyChanged  
10.     {  
11.         private String _name = "Zhang San";  
12.         private int _age = 24;  
13.         private String _hobby = "Basketball";  
14.             
15.         public String Name  
16.         {  
17.             set  
18.             {  
19.                 _name = value;  
20.                 if (PropertyChanged != null)//Changed  
21.                 {  
22.                     PropertyChanged(this, new PropertyChangedEventArgs("Name"));//Monitor Name  
23.                 }  
24.             }  
25.             get  
26.             {  
27.                 return _name;  
28.             }  
29.         }  
30.   
31.         public int Age  
32.         {  
33.             set  
34.             {  
35.                 _age = value;  
36.                 if (PropertyChanged != null)  
37.                 {  
38.                     PropertyChanged(this, new PropertyChangedEventArgs("Age"));//Monitor Age  
39.                 }  
40.             }  
41.             get  
42.             {  
43.                 return _age;  
44.             }   
45.         }  
46.         public String Hobby//No monitoring of Hobby  
47.         {  
48.             get { return _hobby; }  
49.             set { _hobby = value; }  
50.         }  
51.         public event PropertyChangedEventHandler PropertyChanged;  
52.     }  
53. }  

In the Person class defined above, we listened to the Name and Age attributes, but not to the bby.

The contents defined in MainWindow.xmal interface file are as follows:

1. <Window x:Class="WpfApp.MainWindow"  
2.         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
3.         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  
4.         Title="MainWindow" Height="300" Width="350">  
5.     <Grid Name="grid">   
6.         <TextBox Height="20" Text="{Binding Path=Name}"  HorizontalAlignment="Left" Margin="63,12,0,0" Name="textBox1" VerticalAlignment="Top" Width="139" />  
7.         <TextBox Height="20"  Text="{Binding Path=Age}"  HorizontalAlignment="Left" Margin="63,48,0,0" Name="textBox2" VerticalAlignment="Top" Width="139" />  
8.         <TextBox Height="20" Text="{Binding Path=Hobby}"  HorizontalAlignment="Left" Margin="63,82,0,0" Name="textBox3" VerticalAlignment="Top" Width="139" />  
9.           
10.         <Button Content="Display user information" Height="26" HorizontalAlignment="Left" Margin="60,118,0,0" Name="button1" VerticalAlignment="Top" Width="144" Click="button1_Click" />  
11.         <Button Content="Modify user information" Height="26" HorizontalAlignment="Left" Margin="60,158,0,0" Name="button2" VerticalAlignment="Top" Width="144" Click="button2_Click" />  
12.   
13.         <TextBlock Height="40" HorizontalAlignment="Left" Margin="13,201,0,0" Name="textBlock1"   Text="{Binding Path=Name}"  VerticalAlignment="Top" Width="88" />  
14.         <TextBlock Height="40" HorizontalAlignment="Left" Margin="118,201,0,0" Name="textBlock2" Text="{Binding Path=Age}" VerticalAlignment="Top" Width="88" />  
15.         <TextBlock Height="40" HorizontalAlignment="Left" Margin="222,201,0,0" Name="textBlock3" Text="{Binding Path=Hobby, Mode=TwoWay}" VerticalAlignment="Top" Width="88" />  
16.     </Grid>  
17. </Window>  

The background code is:

1. using System;  
2. using System.Collections.Generic;  
3. using System.Linq;  
4. using System.Text;  
5. using System.Windows;  
6. using System.Windows.Controls;  
7. using System.Windows.Data;  
8. using System.Windows.Documents;  
9. using System.Windows.Input;  
10. using System.Windows.Media;  
11. using System.Windows.Media.Imaging;  
12. using System.Windows.Navigation;  
13. using System.Windows.Shapes;  
14.   
15. namespace WpfApp  
16. {  
17.     /// <summary>  
18.     ///Interaction logic of MainWindow.xaml  
19.     /// </summary>  
20.     public partial class MainWindow : Window  
21.     {  
22.         public MainWindow()  
23.         {  
24.             InitializeComponent();  
25.         }  
26.   
27.         private Person p1 = new Person();  
28.         private void button1_Click(object sender, RoutedEventArgs e)  
29.         {  
30.             grid.DataContext = p1;//Binding data  
31.             p1.Name = "Li Si";   

1.             p1.Hobby = "Football";  
2.         }   
3.         private void button2_Click(object sender, RoutedEventArgs e)  
4.         {     
5.             p1.Age = p1.Age + 1;  
6.             p1.Hobby = "Football";  
7.         }  
8.     }  
9. }  

When clicking to display user data

Let's see where the information comes from?

Because there is no monitoring of hobby in Person, p1.Hobby = "football" does not work. When you click modify user information, you cannot modify the corresponding hobby information bound to the interface (even if Mode=TwoWay is written in the interface, you cannot bind).

So when using INotifyPropertyChanged, you need to set the display of the properties to be bound. Otherwise, the two-way binding cannot be performed, that is, the binding is invalid.