Question

如何在Java中引发自定义事件和句柄。一些链接会有所帮助。

感谢。

Answer 1

Java中没有一流的事件。所有事件处理都使用接口和侦听器模式完成。例如：

// Roughly analogous to .NET EventArgs
class ClickEvent extends EventObject {
  public ClickEvent(Object source) {
    super(source);
  }
}

// Roughly analogous to .NET delegate
interface ClickListener extends EventListener {
  void clicked(ClickEvent e);
} 

class Button {
  // Two methods and field roughly analogous to .NET event with explicit add and remove accessors
  // Listener list is typically reused between several events

  private EventListenerList listenerList = new EventListenerList();

  void addClickListener(ClickListener l) {
    clickListenerList.add(ClickListener.class, l)
  }

  void removeClickListener(ClickListener l) {
    clickListenerList.remove(ClickListener.class, l)
  }

  // Roughly analogous to .net OnEvent protected virtual method pattern -
  // call this method to raise the event
  protected void fireClicked(ClickEvent e) {
    ClickListener[] ls = listenerList.getListeners(ClickEvent.class);
    for (ClickListener l : ls) {
      l.clicked(e);
    }
  }
}

客户端代码通常使用匿名内部类来注册处理程序：

Button b = new Button();
b.addClickListener(new ClickListener() {
  public void clicked(ClickEvent e) {
    // handle event
  }
});

Answer 2

Java缺乏内部事件处理，但有一些库可以帮助您实现这一目标。查看javaEventing，http://code.google.com/p/javaeventing/ 它在C＃中的工作方式与您首先定义事件，然后注册事件侦听器一样。您可以使用EventManager.triggerEvent（.. someEvent）触发事件。它还允许您为事件提供自定义条件和有效负载。

鲍勃

Answer 3

Java没有内置支持C＃等委托和事件。您需要自己实施Observer或Publish/Subscribe模式。

Answer 4

如果您正在寻找.net类型的委托事件，我建议使用这个模板解决方案。它的优点是不需要硬强制转换，只要侦听器使用不同的事件类，它就可以实现几个“事件”。

import java.util.EventListener;
import java.util.EventObject;
// replaces the .net delegate

public interface GenericEventListener<EventArgsType extends EventObject>
    extends EventListener {
    public void eventFired(EventArgsType e);
}

//------------------------------------------------

import java.util.EventObject;
import java.util.Vector;
// replaces the .net Event keyword

public class GenericEventSource<EventArgsType extends EventObject> {
    private Vector<GenericEventListener<EventArgsType>> listenerList =
        new Vector<GenericEventListener<EventArgsType>>();

    //TODO handle multi-threading lock issues
    public void addListener(GenericEventListener<EventArgsType> listener) {
        listenerList.add(listener);
    }

    //TODO handle multi-threading lock issues
    public void raise(EventArgsType e) {
        for (GenericEventListener<EventArgsType> listener : listenerList) {
            listener.eventFired(e);
        }
    }
}

//------------------------------------------------

// like a .net class extending EventArgs
public class MyCustomEventArgs extends EventObject {
    private int arg;
    public MyCustomEventArgs(Object source, int arg) {
        super(source);
        this.arg = arg;
    }
    public int getArg() {
        return arg;
    }
}

//------------------------------------------------

// replaces the .net event handler function. Can be put in a nested class, Java style
// Listener can handle several event types if they have different EventArg classes
public class MyCustomListener implements GenericEventListener<MyCustomEventArgs> {
    private Object source = null;
    private int arg;
    public void eventFired(MyCustomEventArgs e) {
        source = e.getSource();
        arg = e.getArg();
        // continue handling event...
    }
}

//------------------------------------------------

import GenericEventListener;
import GenericEventSource;
// this is the class that would like to throw events (e.g. MyButton)
public class MyCustomEventSource {
    // This is like declaring a .net public Event field of a specific delegate type
    GenericEventSource<MyCustomEventArgs> myEvent = new GenericEventSource<MyCustomEventArgs>();

    public GenericEventSource<MyCustomEventArgs> getEvent() {
        return myEvent;
    }
}

//------------------------------------------------

// Examples of using the event
MyCustomListener myListener1 = new MyCustomListener();
MyCustomEventSource mySource = new MyCustomEventSource();
mySource.getEvent().addListener( myListener1 );
mySource.getEvent().raise( new MyCustomEventArgs(mySource,5));

Answer 5

以下链接帮助我理解。

http://www.javaworld.com/javaworld/javaqa/2002-03/01-qa-0315-happyevent.html

Answer 6

Java没有对事件处理的语言支持。但是有些课程可以提供帮助。你可以看java.awt.Event课; java.awt.event和java.beans个包。第一个包是AWT和Swing GUI库中事件处理的基础。 java.beans包包含Java Beans specification的支持内容，包括属性更改事件和bean上下文事件。

通常，事件处理是根据观察者或发布/订阅模式实现的（如kgiannakakis所述）

Java中的事件提升处理

6 个答案: