INotifyPropertyChanged接口在Silverlight中的简单使用

 

INotifyPropertyChanged 接口

INotifyPropertyChanged 接口用于向客户端（通常是执行绑定的客户端）发出某一属性值已更改的通知。

例如，考虑一个带有名为 FirstName 属性的 Person 对象。 若要提供一般性属性更改通知，则 Person 类型实现 INotifyPropertyChanged 接口并在FirstName 更改时引发 PropertyChanged事件。

若要在将客户端与数据源进行绑定时发出更改通知，则绑定类型应具有下列任一功能：

• 实现 INotifyPropertyChanged 接口（首选）。

• 为绑定类型的每个属性提供更改事件。

下面是一个在Silverlight中使用INotifyPropertyChanged接口的简单例子：

XAML代码如下：

<UserControl x:Class="INotifyPropertyChangedDemo.MainPage"
    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"
    mc:Ignorable="d"
    d:DesignHeight="100" d:DesignWidth="300" xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk">

    <Grid x:Name="LayoutRoot" Background="White">
        <Grid.RowDefinitions>
            <RowDefinition Height="40" />
            <RowDefinition Height="40" />
        </Grid.RowDefinitions>
        <sdk:Label HorizontalAlignment="Left" Margin="10,0" Name="lblUserName" Content="姓名：" />
        <sdk:Label HorizontalAlignment="Left" Margin="10,0" Name="lblAge" Content="年龄：" Grid.Row="1" />        
        <TextBox Height="23" Margin="60,0,0,0" Name="txtUserName" Width="120" Text="{Binding Path=UserName}" HorizontalAlignment="Left" />
        <TextBox Height="23" Margin="60,0,0,0" Name="txtAge" Width="120" Text="{Binding Path=Age}" Grid.Row="1" HorizontalAlignment="Left" />
        <Button Height="23" Margin="200,0,0,0" Name="btnHandle" Width="75" Content="更改" Grid.Row="1" HorizontalAlignment="Left" Click="btnHandle_Click" />        
    </Grid>
</UserControl>

C#代码如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.ComponentModel;

namespace INotifyPropertyChangedDemo
{
    public partial class MainPage : UserControl
    {
        User user = User.CreateNewUser();

        public MainPage()
        {
            InitializeComponent();
            txtUserName.DataContext = user;
            txtAge.DataContext = user;
            //user.PropertyChanged += new PropertyChangedEventHandler(user_PropertyChanged);
        }

        //void user_PropertyChanged(object sender, PropertyChangedEventArgs e)
        //{
        //    MessageBox.Show(e.PropertyName);
        //}

        private void btnHandle_Click(object sender, RoutedEventArgs e)
        {
            user.Age = 55;
        }
    }

    public class User : INotifyPropertyChanged
    {
        private User() 
        {
            UserName = "ruby";
            Age = 23;
        }

        public static User CreateNewUser()
        {
            return new User();                
        }

        #region Declare Field

        private string userName;

        public string UserName
        {
            get { return userName; }
            set 
            { 
                if (value != userName)
                {
                    userName = value;
                    OnPropertyChanged("UserName");
                }
            }
        }

        private int age;

        public int Age
        {
            get { return age; }
            set 
            {
                if (value != age)
                {
                    age = value;
                    OnPropertyChanged("Age");
                }                
            }
        }

        #endregion

        #region INotifyPropertyChanged Members

        public event PropertyChangedEventHandler PropertyChanged;

        private void OnPropertyChanged(string propertyName)
        {
            PropertyChangedEventHandler handler = this.PropertyChanged;
            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        #endregion
    }

}

 源码下载

 

个人理解：在XAML中自动更新数据的功能原理是这样的。

1. 首先它自动注册了一个事件。

   user.PropertyChanged += new PropertyChangedEventHandler(user_PropertyChanged);

2. 实现了这个事件的代码程序

   void user_PropertyChanged(object sender, PropertyChangedEventArgs e)
   {
   }

3. 在事件处理程序中根据传进来的字段名称，更改了Silverlight界面中的对应数据