1.IdleHandler是一个interface
public final class MessageQueue {public static interface IdleHandler {boolean queueIdle();}
}2.当MessageQueue无Message
如果mIdleHandlers有IdleHandler需要执行，则触发IdleHandler
public final class MessageQueue {private final ArrayList<IdleHandler> mIdleHandlers = new ArrayList<IdleHandler>();private IdleHandler[] mPendingIdleHandlers;Message next() {int pendingIdleHandlerCount = -1; // -1 only during first iterationfor (;;) {synchronized (this) {//如果没有Message第一次是因为 pendingIdleHandlerCount = -1 ，取一次 idleHandler 数量// If first time idle, then get the number of idlers to run.// Idle handles only run if the queue is empty or if the first message// in the queue (possibly a barrier) is due to be handled in the future.if (pendingIdleHandlerCount < 0&& (mMessages == null || now < mMessages.when)) {pendingIdleHandlerCount = mIdleHandlers.size();}//这次判断大小是确认是否有需要处理的 idlHandler//如果没有的话，则将 mBlocked 改为阻塞状态if (pendingIdleHandlerCount <= 0) {// No idle handlers to run. Loop and wait some more.mBlocked = true;continue;}//如果有需要执行的 idleHandler，创建mPendingIdleHandlers数组if (mPendingIdleHandlers == null) {mPendingIdleHandlers = new IdleHandler[Math.max(pendingIdleHandlerCount, 4)];}//把数组列表中的 idleHandler 复制一份到数组中mPendingIdleHandlers = mIdleHandlers.toArray(mPendingIdleHandlers);//遍历数组mPendingIdleHandlers// Run the idle handlers.// We only ever reach this code block during the first iteration.for (int i = 0; i < pendingIdleHandlerCount; i++) {final IdleHandler idler = mPendingIdleHandlers[i];//release the reference to the handlermPendingIdleHandlers[i] = null; boolean keep = false;try {//执行 idleHandler.queueIdle() 方法。keep = idler.queueIdle();} catch (Throwable t) {Log.wtf(TAG, "IdleHandler threw exception", t);}//根据 idler.queueIdle() 返回结果判断该消息是否从数组列表中移除。if (!keep) {synchronized (this) {mIdleHandlers.remove(idler);}}}//重置数量，保证每次 next() 时，只会执行一次 IdleHandler 方法。// Reset the idle handler count to 0 so we do not run them again.pendingIdleHandlerCount = 0;// While calling an idle handler, a new message could have been delivered// so go back and look again for a pending message without waiting.nextPollTimeoutMillis = 0;}}}
}3.添加IdleHandler
public final class MessageQueue {public void addIdleHandler(@NonNull IdleHandler handler) {if (handler == null) {throw new NullPointerException("Can't add a null IdleHandler");}synchronized (this) {mIdleHandlers.add(handler);}}
}4.移除IdleHandler
public final class MessageQueue {public void removeIdleHandler(@NonNull IdleHandler handler) {synchronized (this) {mIdleHandlers.remove(handler);}}
}
)
