模拟android Handler线程间通信

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消息类：

package p;public class Message {Runnable runnable;private long start;long delay;Handler target;public int arg;public Message(Handler target) {this.target = target;start = System.currentTimeMillis();}boolean canHandle() {return delay <= System.currentTimeMillis() - start;}}

消息队列类：

package p;import java.util.ArrayList;import java.util.List;public class MessageQueue {private List<Message> messages = new ArrayList<Message>();private int cursor = -1;/** * 入队 *  * @param message */public void push(Message message) {messages.add(message);}/** * 移出队列 *  * @param message */public void remove(Message message) {messages.remove(message);cursor--;}/** * 出队 *  * @return */public Message pop() {Message message = null;if (!messages.isEmpty()) {message = messages.get(++cursor);if (cursor == messages.size() - 1) {cursor = -1;}}return message;}}

Handler类：

package p;public class Handler {private MessageQueue queue;public Handler() {queue = MessageManager.getMessageQueue();if (queue == null) {throw new RuntimeException("创建Handler之前必须必须调用MessageManager.prepare()");}}/** * 接收消息，子类去实现 *  * @param message */public void handleMessage(Message message) {}/** * 发送消息 *  * @param message * @param delay */public void sendMessage(Message message, long delay) {message.delay = delay;queue.push(message);}/** * 发送任务 *  * @param runnable * @param delay */public void post(Runnable runnable, long delay) {Message message = convertToMessage(runnable);message.delay = delay;queue.push(message);}/** * 将任务转化为消息 *  * @param runnable * @return */private Message convertToMessage(Runnable runnable) {Message message = new Message(this);message.runnable = runnable;return message;}/** * 分派消息 *  * @param message */void dispatchMessage(Message message) {if (message.runnable != null) {message.runnable.run();} else {handleMessage(message);}}}

消息管理类：

package p;public class MessageManager {private static ThreadLocal<MessageQueue> local = new ThreadLocal<MessageQueue>();/** * 获取消息队列 *  * @return */public static MessageQueue getMessageQueue() {return local.get();}/** * 创建消息队列 */public static void prepare() {MessageQueue queue = local.get();if (queue != null) {throw new RuntimeException("每个线程只能有一个消息队列！");}local.set(new MessageQueue());}/** * 开启消息循环 */public static void loop() {MessageQueue messageQueue = local.get();Message message;while (true) {if ((message = messageQueue.pop()) != null) {if (message.canHandle()) {messageQueue.remove(message);message.target.dispatchMessage(message);}}}}}

模拟activity以及启动：

package p.client;import p.Handler;import p.Message;import p.MessageManager;public class UI2 {private Handler handler;public void onCreate() {System.out.println("onCreate:" + Thread.currentThread().getName());handler = new Handler() {@Overridepublic void handleMessage(Message message) {System.out.println("handleMessage:"+ Thread.currentThread().getName());System.out.println(message.arg);}};new Thread(new Runnable() {@Overridepublic void run() {try {Thread.sleep(3000);System.out.println("sendMessage:"+ Thread.currentThread().getName());} catch (InterruptedException e) {e.printStackTrace();}Message message = new Message(handler);message.arg = 10;handler.sendMessage(message, 3000);}}).start();System.out.println("End onCreate!");}public static void main(String[] args) {Runnable runnable = new Runnable() {@Overridepublic void run() {MessageManager.prepare();UI2 mainUI = new UI2();mainUI.onCreate();MessageManager.loop();}};Thread main = new Thread(runnable);main.setName("main");main.start();}}

输出：

onCreate:mainEnd onCreate!sendMessage:Thread-1handleMessage:main10

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