为什么我不能从一个扩展方法调用PropertyChanged事件？ [英] Why can't I invoke PropertyChanged event from an Extension Method?

问题描述

我试图代码的类，以避免像RaisePropertyChanged的方法。我知道我可以从有实施类继承，但在某些情况下，我不能。我已经试过了扩展方法，但Visual Studio的抱怨。

 公共静态类扩展
 {
公共静态无效RaisePropertyChanged（这INotifyPropertyChanged的谓词，字符串propertyName的）
 {
如果（predicate.PropertyChanged！= NULL）
 {
 predicate.PropertyChanged（propertyName的，新的PropertyChangedEventArgs（propertyName的） ）; 
} 
} 
} 
  

它说：

事件
'的 System.ComponentModel.INotifyPropertyChanged.PropertyChanged'可以
只出现在左侧的+ =或 - = 的

解决方案

的里德是正确的。不过，我看你想要做什么（使你的代码reusable- 对你有好处）;而我只想指出，这往往容易被接受 PropertyChangedEventHandler 的代表的本身，并从 INotifyPropertyChanged的实施

 公共静态无效抬起（这PropertyChangedEventHandler处理程序，对象发件人，字符串propertyName的） 
 {
如果
 {
处理器（发件人，新PropertyChangedEventArgs（propertyName的））（处理！= NULL）; 
} 
} 
  

这是您的类，它实现<$ C $内再C> INotifyPropertyChanged的，你可以调用像这样这个扩展的方法：

  PropertyChanged.Raise（这一点， myProperty的）; 
  

这工作，因为，的为马克说，类中声明你的事件可以的访问它像场（这意味着你可以把它作为一个委托参数的方法，包括扩展方法）。

I've tried to code a class to avoid a method like "RaisePropertyChanged". I know that I can inherit from a class that has that implementation but in some cases I can't. I've tried with a Extension Method but Visual Studio complain.

public static class Extension
{
    public static void RaisePropertyChanged(this INotifyPropertyChanged predicate, string propertyName)
    {
        if (predicate.PropertyChanged != null)
        {
            predicate.PropertyChanged(propertyName, new PropertyChangedEventArgs(propertyName));
        }
    }
}

It said:

"The event 'System.ComponentModel.INotifyPropertyChanged.PropertyChanged' can only appear on the left hand side of += or -="

解决方案

Reed is right. However, I see what you're trying to do (make your code reusable—good for you); and I'll just point out that this is often easily rectified by accepting the PropertyChangedEventHandler delegate itself and passing it from within the INotifyPropertyChanged implementation:

public static void Raise(this PropertyChangedEventHandler handler, object sender, string propertyName)
{
    if (handler != null)
    {
        handler(sender, new PropertyChangedEventArgs(propertyName));
    }
}

Then from within your class which implements INotifyPropertyChanged, you can call this extension method like so:

PropertyChanged.Raise(this, "MyProperty");

This works because, as Marc said, within the class declaring the event you can access it like a field (which means you can pass it as a delegate argument to a method, including extension methods).

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