观察者机制 在非UI线程中访问UI

package com.shishuo.myplugin1.test;

public class Main {
    private static int count=0;
    private static Thread thread;
    public static void update(){
        new Thread{
            //建立一个新的线程，实现每隔三秒count累加一次，到10后变为0
            public void run(){
                while(count<=10){
                    //在线程中加入监听机制，旨在实现count每一次发生变化都会触发监听事件
                    //EventProducer是事件源
                    EventProducer producer=new EventProducer();
                    //为事件源添加监听器，参数为监听事件
                    producer.addListener(new EventConsumer);
                    //触发
                    producer.setValue(""+count);
                    try{
                        Thread.sleep(3000);
                    }catch（Exception e）{
                        e.printStackTrace();
                    }
                    count++;
                    if(count==10){
                        count=0;
                    }
                }
            }
        }.start();
    }
}

package com.shishuo.myplugin1.test;

public class EventProducer{
    //监听器要在事件源上注册
    ListenerRegister register=new ListenerRegister();
    private String value="";
    public String getValue(){
        return value;
    }
    public void setValue(String newValue){
        //当有事件触发时，事件源要把事件传递给监听器，监听器会根据事件对象采取相应的方法响应这个事件
        value=newValue;
        ValueChangeEvent event=new ValueChangeEvent(this,value);
        fireAEvent(event);
    }
    public void addListener(ValueChangeListener a){
        register.addListener(a);
    }
    public void removeListener(ValueChangeListener){
        register.removeListener(a);
    }
    public void fireAEvent(ValueChangeEvent event){
        register.fireAEvent;
    }
}

package com.shishuo.myplugin1.test;

import java.util.Vector;
public class ListenerRegister{
    //存放监听器的Vector
    private Vector<ValueChangeListener> listeners=new Vector<ValueChangeListener>();
    public synchronized void addListener(ValueChangeListener a){
        listeners.addElement(a);
    }
    
    public synchronized void removeListener(ValueChangeListener a){
        listeners.removeElement(a);
    }
    
    public void fireAEvent(ValueChangeEvent evt){
        Vector<ValueChangeEvent> currentListeners=null;
        synchronized(this){
            currentListener=(Vector<ValueChangeEvent>)listeners.clone();
        }
        for(int i;i<currentListener.size();i++){
            //事件发生后，监听器接收来自事件源的事件，根据不同的事件调用相应的方法
            //遍历监听器数组中的监听器，根据事件调用相应的响应方法
            ValueChangeListener listener=(ValueChangeListener)currentListeners.elementAt(i);
            listener.performed(evt);
        }
    }
}

package com.shishuo.myplugin1.test;

import java.util.EventObject;
//事件
public class ValueChangeEvent extends EventObject
{
  private static final long serialVersionUID=767352958358520268L;
  private String value;
  public ValueChangeEvent(Object source){
      this(source,"0");
  }
  public ValueChangeEvent(Object source,String newValue){
      super(source);
      value=newValue;
  }
  public String getValue(){
      return value;
  }
}

package com.shishuo.myplugin1.test;

import java.util.EventListener;
//监听器接口
public interface ValueChangeListener extends EventListener{
    public abstract void performed(ValueChangeEvent e);
}

package com.shishuo.myplugin1.test;

import org.eclipse.swt.widgets.*;
import com.shishuo.myplugin1.test.Views.view1;
public class EventConsumer implements ValueChangeListener{
    //以下方法是事件发生后采取的动作
    @Override
    public void performed(final ValueChangeEvent e){
        //在非UI线程中访问UI，必须要有以下语句否则会报以下异常
        Display.getDefault().syncExec(new Runnable(){
            public void run(){
                
                //这里写对SWT控件的设置
                Text text=View1.text1;
                text.setText(""+e.getValue());
            }
        });
    }
    
    
}

不添加syncExec语句会报以下异常：

Exception in thread "Thread-0" org.eclipse.swt.SWTException: Invalid thread access
    at org.eclipse.swt.SWT.error(SWT.java:4441)
    at org.eclipse.swt.SWT.error(SWT.java:4356)
    at org.eclipse.swt.SWT.error(SWT.java:4327)
    at org.eclipse.swt.widgets.Widget.error(Widget.java:476)
    at org.eclipse.swt.widgets.Widget.checkWidget(Widget.java:367)
    at org.eclipse.swt.widgets.Text.getText(Text.java:1350)
    at test.Snippet108$1$1.run(Snippet108.java:24)

最后的结果就是在Text中每隔三秒更新一次显示内容为0~9