为什么 OnPropertyChanged 在代码隐藏中不起作用? [英] Why does OnPropertyChanged not work in Code Behind?

问题描述

我试图通过将 ViewModel 模型放入后面的代码并将 DataContext 绑定为this"来简化一些代码，但它的工作方式似乎有所不同，在以下示例中:

I'm trying to simplify some code by putting the ViewModel models into the code behind and binding the DataContext as "this", but it seems to work differently, in the following example:

为什么点击按钮时，绑定到Message"的TextBlock却没有变化，即使调用了OnPropertyChanged("Message")?

XAML:

<Window x:Class="TestSimple223.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">
    <StackPanel HorizontalAlignment="Left">
        <Button Content="Button" 
                Click="button1_Click" />
        <TextBlock 
            Text="{Binding Path=Message, Mode=TwoWay}"/>
        <TextBlock
            x:Name="Message2"/>
    </StackPanel>
</Window>

背后的代码:

using System.Windows;
using System.ComponentModel;

namespace TestSimple223
{
    public partial class Window1 : Window
    {
        #region ViewModelProperty: Message
        private string _message;
        public string Message
        {
            get
            {
                return _message;
            }

            set
            {
                _message = value;
                OnPropertyChanged("Message");
            }
        }
        #endregion

        public Window1()
        {
            InitializeComponent();
            DataContext = this;

            Message = "original message";
            Message2.Text = "original message2";
        }

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            Message = "button was clicked, message changed";
            Message2.Text = "button was click, message2 changed";
        }

        #region INotify
        public event PropertyChangedEventHandler PropertyChanged;

        protected void OnPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        } 
        #endregion


    }
}

推荐答案

您尚未将您的课程标记为可用于属性更改通知.把标题改成

You haven't marked your class as being available for property change notification. Change the heading to

public partial class Window1 : Window, INotifyPropertyChanged

仅仅因为您实现了方法并不意味着 WPF 知道一个类支持更改通知 - 您需要通过用 INotifyPropertyChanged 标记来告诉它.这样，绑定机制可以将您的类识别为潜在的更新目标.

Just because you implement the methods doesn't mean that WPF knows that a class supports change notification - you need to tell it by marking it with INotifyPropertyChanged. This way, the binding mechanism can identify your class as a potential update target.

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