Java中的事件引發處理

Question

如何引發Java中的自定義事件和處理。一些鏈接將會有所幫助。

謝謝。

Answer 1

以下鏈接幫助我瞭解。

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

Answer 2

Java尚未內置對C＃等代表和事件的支持。您需要自行實施Observer或Publish/Subscribe模式。

Answer 3

Java對事件處理沒有語言支持。但是有些課程可以提供幫助。你可以看看java.awt.Event class; java.awt.event和java.beans包。第一個包是AWT和Swing GUI庫中事件處理的基礎。 java.beans包包含支持Java Beans specification的東西，包括屬性更改事件和bean上下文事件。

通常，事件處理是根據觀測器實現或發佈/訂閱的模式（如由kgiannakakis提及）

Answer 4

有在Java中沒有一流事件。所有事件處理都是使用接口和偵聽器模式完成的。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); 
    } 
    } 
} 

客戶代碼通常使用匿名內部類註冊處理程序：

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

Answer 5

的Java缺乏內在的事件處理，但也有庫，幫助你做到這一點。查看javaEventing，http://code.google.com/p/javaeventing/ 它的工作原理與C＃中的相似，您首先定義事件，然後註冊事件偵聽器。您使用EventManager.triggerEvent（.. someEvent）觸發事件。它允許您爲事件提供自定義條件和有效載荷。

鮑勃

Answer 6

如果你正在尋找一個.NET類型的委託時，我提出這個模板化的解決方案。 它的優點是不需要強制轉換，只要使用不同的事件類，偵聽器就可以實現多個「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));