从基类中提升事件

Question

我知道可以在类中引发一个实现声明发生的事件,但我希望在基类级别引发事件并引发派生类的事件:

public interface IFoo
{
    event EventHandler<FooEventArgs> FooValueChanged;
    void RaiseFooValueChanged(IFooView sender, FooEventArgs  e);
}

[TypeDescriptionProvider(typeof(FooBaseImplementor))]
public abstract class FooBase : Control, IFoo
{
    public virtual event EventHandler<FooEventArgs> FooValueChanged;

    public void RaiseFooValueChanged(IFooView sender, FooEventArgs e)
    {
        FooValueChanged(sender, e);
    }
}

我不能拥有FooValueChanged事件摘要,因为基类不能引发事件.当前代码运行,但调用FooValueChanged(sender,e)抛出NullReferenceException,因为它不调用派生类的事件,只调用基类的事件.

我哪里错了？

我可以将事件和提升者都抽象化,但是我需要记住在每个派生类中调用FooValueChanged(sender,e).我试图避免这种情况,同时能够使用Visual Studio设计器进行派生控件.

Answer 1

首先请注意,您使用的事件声明是C#中的简写符号:

public event EventHandler Event;
public void RaiseEvent() {
    this.Event(this, new EventArgs());
}

相当于:

private EventHandler backEndStorage;
public event EventHandler Event {
    add { this.backEndStorage += value; }
    remove { this.backEndStorage -= value; }
}
public void RaiseEvent() {
    this.backEndStorage(this, new EventArgs());
}

backEndStorage是一个多播委托.

现在您可以重写代码:

public interface IFoo
{
    event EventHandler<FooEventArgs> FooValueChanged;
    void RaiseFooValueChanged(IFooView sender, FooEventArgs  e);
}

[TypeDescriptionProvider(typeof(FooBaseImplementor))]
public abstract class FooBase : Control, IFoo
{
    protected event EventHandler<FooEventArgs> backEndStorage;
    public event EventHandler<FooEventArgs> FooValueChanged {
        add { this.backEndStorage += value; }
        remove { this.backEndStorage -= value; }
    }

    public void RaiseFooValueChanged(IFooView sender, FooEventArgs e)
    {
        this.backEndStorage(sender, e);
    }
}

public class FooDerived : FooBase {
    public event EventHandler<FooEventArgs> AnotherFooValueChanged {
        add { this.backEndStorage += value; }
        remove { this.backEndStorage -= value; }
    }
}

所以现在当在派生类上添加事件时,它们实际上将被添加到基类的backEndStorage中,因此允许基类调用在派生类中注册的委托.