手写Handler

ActivityThread.java:

package com.metre.core;

public class ActivityThread {

    public static void main(String[] args) throws Exception {
         
        //初始化全局唯一主线程的Looper对象，和MessageQueue消息队列
        Looper.prepare();
        
        
        final Handler handler = new Handler() {
            @Override
            public void handleMessage(Message msg) {
                super.handleMessage(msg);
                System.out.println(msg.toString());
            }
        };
        
        new Thread(new Runnable() {

            @Override
            public void run() {
                Message message = new Message();
                message.obj = "你好 小米!";
                handler.sendMessage(message);
                
            }
            
        }).start();
        
        //循环取出消息
        Looper.loop();

    }

}

Handler.java :

package com.metre.core; 
public class Handler {

    MessageQueue mQueue;
    
    public Handler() throws Exception {
        Looper looper = Looper.myLooper();
        if(looper == null) {
            throw new Exception("Can't create Handler inside thread "+Thread.currentThread()+" that has not called Looper.prepare()");
        }
        mQueue = looper.mQueue;
    }
    
    public void sendMessage(Message msg) {
        
        
        enqueueMessage(msg);
    }
    private void enqueueMessage(Message msg) {
        msg.target = this;
        mQueue.enqueueMessage(msg);
    }
    public void handleMessage(Message msg) {
        
    }
    
    public void dispatchMessage(Message msg) {
        handleMessage(msg);
    }
}

Looper.java

package com.metre.core;

public class Looper {

    static ThreadLocal mThreadLocal = new ThreadLocal();
    
    static MessageQueue mQueue;
    
    public Looper() {
        mQueue =  new MessageQueue();
    }
    public static void prepare() throws Exception{
        if(mThreadLocal.get() != null) {
            throw new Exception("Only one Looper may be created per Thread.");
        }
        
        mThreadLocal.set(new Looper());
    }
    
    public static void loop() {
        
        while(true) {
            Message message = mQueue.next();
            message.target.dispatchMessage(message);
        }
        
    }
    
    public static Looper myLooper(){
        return (Looper)mThreadLocal.get();
    }
}

Message.java:

package com.metre.core;

public class Message {

    public Object obj;
    public Handler target;
    public int what;
    @Override
    public String toString() {
        return "Message [obj=" + obj.toString() + "]";
    }
    
    
}

MessageQueue.java

package com.metre.core;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;

public class MessageQueue {

    BlockingQueue blockingQueue = new ArrayBlockingQueue(50);
    
    public void enqueueMessage(Message msg) {
        try {
            blockingQueue.put(msg);
        } catch (InterruptedException e) { 
            e.printStackTrace();
        }
    }
    public  Message next() {
        try {
            return blockingQueue.take();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return null;
    }
}