private static final int MESSAGA_TEST_1 = 1; /** * 主线程有初始化好Looper，所以在主线程处理消息 */ private Handler mHandler = new Handler(new Handler.Callback() { @OverrIDe public boolean handleMessage(@NonNull Message msg) { switch (msg.what) { case MESSAGA_TEST_1: if (tvTest != null) { //传递消息obj tvTest.setText((String) msg.obj); } break; } return false; } }); private Handler mHandler2 = new Handler() { @OverrIDe public voID handleMessage(@NonNull Message msg) { switch (msg.what) { case MESSAGA_TEST_1: if (tvTest != null) { //传递消息obj tvTest.setText((String) msg.obj); } break; } } }; private voID onClick() { //当点击事件执行，就会在子线程发送消息更新textvIEw new Thread(new Runnable() { @OverrIDe public voID run() { clickEndMessage(); } }).start(); } /** * 可以在子线程发送 */ private voID clickEndMessage() { //obtain享元模式 Message message = Message.obtain(mHandler); //what相当于标记 message.what = MESSAGA_TEST_1; //obj传数据 message.obj = new String("baozi"); //普通发送message mHandler.sendMessage(message); . . . //发送标记，不带其他内容，内部会封装成只有标记的Message对象 mHandler.sendEmptyMessage(); //尾部带有Delayed，发送延迟消息，单位毫秒 mHandler.sendMessageDelayed(message, 1000); //尾部带有AtTime,发送消息的时间跟Delayed差别就是Delayed是执行的当前时间+传进去的时间，AtTime就传进去的绝对时间 mHandler.sendMessageAtTime(); //在队列头插入消息 mHandler.sendMessageAtFrontOfQueue(message); } @OverrIDe protected voID onDestroy() { if(mHandler!=null){ //关闭activity时，移除消息 mHandler.removeMessages(MESSAGA_TEST_1); mHandler = null; } super.onDestroy(); }复制代码tvTest.postDelayed(new Runnable() { @OverrIDe public voID run() { tvTest.setText("5s"); }},5*1000);/** * VIEw 源码 */public boolean postDelayed(Runnable action, long delayMillis) { final AttachInfo attachInfo = mAttachInfo; if (attachInfo != null) { return attachInfo.mHandler.postDelayed(action, delayMillis); } // Postpone the runnable until we kNow on which thread it needs to run. // Assume that the runnable will be successfully placed after attach. getRunQueue().postDelayed(action, delayMillis); return true;}复制代码runOnUiThread(new Runnable() { @OverrIDe public voID run() { //更新UI }}); /** * Activity 源码 */public final voID runOnUiThread(Runnable action) { if (Thread.currentThread() != mUiThread) { mHandler.post(action); } else { action.run(); }}复制代码 private Handler handler2; /** * 子线程 */ private voID thread() { new Thread(new Runnable() { @OverrIDe public voID run() { handler2 = new Handler(new Handler.Callback() { @OverrIDe public boolean handleMessage(@NonNull Message msg) { return false; } }); } }).start(); }复制代码 public static voID main(String[] args) { . . Looper.prepareMainLooper(); . . ActivityThread thread = new ActivityThread(); . . }复制代码 public Handler(@Nullable Callback callback, boolean async) { . . mLooper = Looper.myLooper(); if (mLooper == null) { throw new RuntimeException( "Can't create handler insIDe thread " + Thread.currentThread() + " that has not called Looper.prepare()"); } . . }复制代码 private Handler handler2; /** * 子线程 */ private voID thread() { new Thread(new Runnable() { @OverrIDe public voID run() { Looper.prepare(); Looper looper = Looper.myLooper(); looper.loop(); handler2 = new Handler(looper, new Handler.Callback() { @OverrIDe public boolean handleMessage(@NonNull Message msg) { return false; } }); } }).start(); }复制代码public final class Message implements Parcelable { //用于handler标记处理的 public int what; //可以传递的int参数1 public int arg1; //可以传递的int参数2 public int arg2; //可以传递的obj参数 public Object obj; //执行时间 public long when; //传递的bundle Bundle data; //Message绑定的Handler Handler target; //Handler.post()时传的callback Runnable callback; //链表结构 Message next;复制代码 /** * Return a new Message instance from the global pool. Allows us to * avoID allocating new objects in many cases. */ public static Message obtain() { synchronized (sPoolSync) { if (sPool != null) { Message m = sPool; sPool = m.next; m.next = null; m.flags = 0; // clear in-use flag sPoolSize--; return m; } } return new Message(); }复制代码 /** * Return a Message instance to the global pool. * <p> * You MUST NOT touch the Message after calling this function because it has * effectively been freed. It is an error to recycle a message that is currently * enqueued or that is in the process of being delivered to a Handler. * </p> */ public voID recycle() { if (isInUse()) { if (gCheckRecycle) { throw new IllegalStateException("This message cannot be recycled because it " + "is still in use."); } return; } recycleUnchecked(); }复制代码 private static final int MAX_POol_SIZE = 50; @UnsupportedAppUsage voID recycleUnchecked() { // Mark the message as in use while it remains in the recycled object pool. // Clear out all other details. flags = FLAG_IN_USE; what = 0; arg1 = 0; arg2 = 0; obj = null; replyTo = null; sendingUID = UID_NONE; workSourceUID = UID_NONE; when = 0; target = null; callback = null; data = null; synchronized (sPoolSync) { //最多50个 if (sPoolSize < MAX_POol_SIZE) { next = sPool; sPool = this; sPoolSize++; } } }复制代码 boolean enqueueMessage(Message msg, long when) { //handler为空就报异常 if (msg.target == null) { throw new IllegalArgumentException("Message must have a target."); } //加锁 synchronized (this) { //消息正在使用会报错 if (msg.isInUse()) { throw new IllegalStateException(msg + " This message is already in use."); } //判断线程是否存活 if (mQuitting) { IllegalStateException e = new IllegalStateException( msg.target + " sending message to a Handler on a dead thread"); Log.w(TAG, e.getMessage(), e); msg.recycle(); return false; } //标记正在使用 msg.markInUse(); msg.when = when; //链表头 Message p = mMessages; boolean neeDWake; if (p == null || when == 0 || when < p.when) { //如果队列为空，或者消息延迟时间为0，或者延迟时间小于mMessage的，就插入在头部 // New head, wake up the event queue if blocked. msg.next = p; mMessages = msg; //唤醒队列 neeDWake = mBlocked; } else { // Inserted within the mIDdle of the queue. Usually we don't have to wake // up the event queue unless there is a barrIEr at the head of the queue // and the message is the earlIEst asynchronous message in the queue. //插入队列中间。通常，除非队列的开头有障碍并且消息是队列中最早的异步消息，否则我们不必唤醒事件队列。 neeDWake = mBlocked && p.target == null && msg.isAsynchronous(); Message prev; //在中间插入，根据时间位置插入 for (;;) { prev = p; p = p.next; if (p == null || when < p.when) { break; } if (neeDWake && p.isAsynchronous()) { neeDWake = false; } } msg.next = p; // invariant: p == prev.next prev.next = msg; } //是否唤醒 // We can assume mPtr != 0 because mQuitting is false. if (neeDWake) { nativeWake(mPtr); } } return true; }复制代码 @UnsupportedAppUsage Message next() { // Return here if the message loop has already quit and been disposed. // This can happen if the application trIEs to restart a looper after quit // which is not supported. final long ptr = mPtr; if (ptr == 0) { return null; } int pendingIDleHandlerCount = -1; // -1 only during first iteration int nextPollTimeoutMillis = 0; for (;;) { if (nextPollTimeoutMillis != 0) { Binder.flushPendingCommands(); } //没消息取就阻塞 nativePollOnce(ptr, nextPollTimeoutMillis); synchronized (this) { // Try to retrIEve the next message. Return if found. final long Now = SystemClock.uptimeMillis(); Message prevMsg = null; Message msg = mMessages; if (msg != null && msg.target == null) { // Stalled by a barrIEr. Find the next asynchronous message in the queue. do { prevMsg = msg; msg = msg.next; } while (msg != null && !msg.isAsynchronous()); } if (msg != null) { if (Now < msg.when) { // Next message is not ready. Set a timeout to wake up when it is ready. //阻塞时间为消息的执行时间减去当前时间 nextPollTimeoutMillis = (int) Math.min(msg.when - Now, Integer.MAX_VALUE); } else { // Got a message. mBlocked = false; if (prevMsg != null) { prevMsg.next = msg.next; } else { mMessages = msg.next; } msg.next = null; if (DEBUG) Log.v(TAG, "Returning message: " + msg); msg.markInUse(); //只有这里返回msg return msg; } } else { //没有更多消息，设置为-1，阻塞 // No more messages. nextPollTimeoutMillis = -1; } . . } }复制代码 voID quit(boolean safe) { //主线程是不能退出的 if (!mQuitAllowed) { throw new IllegalStateException("Main thread not allowed to quit."); } synchronized (this) { if (mQuitting) { return; } mQuitting = true; //移除消息 if (safe) { removeAllFutureMessagesLocked(); } else { removeAllMessagesLocked(); } // We can assume mPtr != 0 because mQuitting was prevIoUsly false. nativeWake(mPtr); } }复制代码 /** * 移除全部消息 */ private voID removeAllMessagesLocked() { Message p = mMessages; while (p != null) { Message n = p.next; p.recycleUnchecked(); p = n; } mMessages = null; } /** * 移除未执行的消息，正在运行的等待完成再回收 */ private voID removeAllFutureMessagesLocked() { final long Now = SystemClock.uptimeMillis(); Message p = mMessages; if (p != null) { if (p.when > Now) { //如果执行时间还未到，即未执行的消息，移除回收 removeAllMessagesLocked(); } else { //等待在执行的消息执行完再回收移除 Message n; for (;;) { n = p.next; if (n == null) { return; } if (n.when > Now) { break; } p = n; } p.next = null; do { p = n; n = p.next; p.recycleUnchecked(); } while (n != null); } } }复制代码 @UnsupportedAppUsage static final ThreadLocal<Looper> sThreadLocal = new ThreadLocal<Looper>();复制代码 /** Initialize the current thread as a looper. * This gives you a chance to create handlers that then reference * this looper, before actually starting the loop. Be sure to call * {@link #loop()} after calling this method, and end it by calling * {@link #quit()}. */ public static voID prepare() { prepare(true); } private static voID prepare(boolean quitAllowed) { //每个线程只能有一个looper if (sThreadLocal.get() != null) { throw new RuntimeException("Only one Looper may be created per thread"); } //初始化后设置给sThreadLocal sThreadLocal.set(new Looper(quitAllowed)); }复制代码 private Looper(boolean quitAllowed) { //创建消息队列 mQueue = new MessageQueue(quitAllowed); //绑定当前线程 mThread = Thread.currentThread(); }复制代码 /** * Return the Looper object associated with the current thread. Returns * null if the calling thread is not associated with a Looper. */ public static @Nullable Looper myLooper() { return sThreadLocal.get(); }复制代码 /** * Run the message queue in this thread. Be sure to call * {@link #quit()} to end the loop. */ public static voID loop() { //拿到当前线程的looper，如果没有prepare（）那就是空，报异常 final Looper me = myLooper(); if (me == null) { throw new RuntimeException("No Looper; Looper.prepare() wasn't called on this thread."); } if (me.mInLoop) { Slog.w(TAG, "Loop again would have the queued messages be executed" + " before this one completed."); } . . . for (;;) { //不停的取消息 Message msg = queue.next(); // might block if (msg == null) { // No message indicates that the message queue is quitting. return; } . . try { //处理消息，msg.target就是绑定的handler msg.target.dispatchMessage(msg); if (observer != null) { observer.messagedispatched(token, msg); } dispatchEnd = needEndTime ? SystemClock.uptimeMillis() : 0; } catch (Exception exception) { if (observer != null) { observer.dispatchingThrewException(token, msg, exception); } throw exception; } finally { ThreadLocalWorkSource.restore(origWorkSource); if (traceTag != 0) { Trace.traceEnd(traceTag); } } . . //回收消息 msg.recycleUnchecked(); } }复制代码 /** * Quits the looper. * <p> * Causes the {@link #loop} method to terminate without processing any * more messages in the message queue. * </p><p> * Any attempt to post messages to the queue after the looper is asked to quit will fail. * For example, the {@link Handler#sendMessage(Message)} method will return false. * </p><p > * Using this method may be unsafe because some messages may not be delivered * before the looper terminates. ConsIDer using {@link #quitSafely} instead to ensure * that all pending work is completed in an orderly manner. * </p> * * @see #quitSafely */ public voID quit() { mQueue.quit(false); } /** * Quits the looper safely. * <p> * Causes the {@link #loop} method to terminate as soon as all remaining messages * in the message queue that are already due to be delivered have been handled. * However pending delayed messages with due times in the future will not be * delivered before the loop terminates. * </p><p> * Any attempt to post messages to the queue after the looper is asked to quit will fail. * For example, the {@link Handler#sendMessage(Message)} method will return false. * </p> */ public voID quitSafely() { mQueue.quit(true); }复制代码 private boolean enqueueMessage(@NonNull MessageQueue queue, @NonNull Message msg, long uptimeMillis) { //消息的target就是handler msg.target = this; msg.workSourceUID = ThreadLocalWorkSource.getUID(); //设置异步 if (mAsynchronous) { msg.setAsynchronous(true); } //消息入队 return queue.enqueueMessage(msg, uptimeMillis); }复制代码 /** * Handle system messages here. */ public voID dispatchMessage(@NonNull Message msg) { //Message 内部的callback，就是Handler,post()方法封装在Message内部的 if (msg.callback != null) { handleCallback(msg); } else { //如果Handler创建时传Callback就执行这里 if (mCallback != null) { //如果返回值为false 就结束 if (mCallback.handleMessage(msg)) { return; } } //如果mCallback为null,或者上面返回值为true,就执行这里 handleMessage(msg); } } /** * Message 内部的callback，就是Handler,post()方法封装在Message内部的 */ private static voID handleCallback(Message message) { message.callback.run(); } /** * 创建时如果传Callback，就执行 */ public interface Callback { /** * @param msg A {@link androID.os.Message Message} object * @return True if no further handling is desired */ boolean handleMessage(@NonNull Message msg); } /** * 创建时如果没传Callback,而是重写了该方法 */ public voID handleMessage(@NonNull Message msg) { }复制代码public class HandlerThread extends Thread { int mPriority; int mTID = -1; Looper mLooper; private @Nullable Handler mHandler; public HandlerThread(String name) { super(name); mPriority = Process.THREAD_PRIORITY_DEFAulT; } @OverrIDe public voID run() { mTID = Process.myTID(); Looper.prepare(); //获得锁创建looper synchronized (this) { mLooper = Looper.myLooper(); notifyAll(); } Process.setThreadPriority(mPriority); onLooperPrepared(); Looper.loop(); mTID = -1; } /** * This method returns the Looper associated with this thread. If this thread not been started * or for any reason isAlive() returns false, this method will return null. If this thread * has been started, this method will block until the looper has been initialized. * @return The looper. */ public Looper getLooper() { if (!isAlive()) { return null; } // If the thread has been started, wait until the looper has been created. synchronized (this) { //如果线程存活而且looper为空，就等待让出锁，直到looper创建 while (isAlive() && mLooper == null) { try { wait(); } catch (InterruptedException e) { } } } return mLooper; }}复制代码整理了一份《AndroID Framework精编内核解析》pdf学习笔记，有需要的同学可以点击这里免费领取！
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