2 Java 代码
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public Handler(){ mLooper = Looper.myLooper(); // 取得当前线程的 Looper，如果抛
异常
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if (mLooper == null) { throw new RuntimeException(
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"Can't create handler inside thread that has not called Looper.prepare()"); }
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mQueue = mLooper.mQueue; // 取得消息队列 mCallback = null;
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}
3 Java 代码
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//不管调用哪个方法，最终执行的是
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public boolean sendMessageAtTime(Message msg, long uptimeMillis){
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boolean sent = false;
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// 取得消息队列
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MessageQueue queue = mQueue;
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if (queue != null) {
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msg.target = this; // 消息发出着是自己
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sent = queue.enqueueMessage(msg, uptimeMillis); // 添加到消息队列中
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}
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else {
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RuntimeException e = new RuntimeException(
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this + " sendMessageAtTime() called with no mQueue");
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Log.w("Looper", e.getMessage(), e);
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}
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return sent;
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}
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final boolean enqueueMessage(Message msg, long when) {
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if (msg.when != 0) {
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throw new AndroidRuntimeException(msg
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+ " This message is already in use.");
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}
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if (msg.target == null && !mQuitAllowed) {
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throw new RuntimeException("Main thread not allowed to quit");
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}
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synchronized (this) {
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if (mQuiting) {
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RuntimeException e = new RuntimeException(
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msg.target + " sending message to a Handler on a dead thread");
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Log.w("MessageQueue", e.getMessage(), e);
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return false;
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} else if (msg.target == null) {
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mQuiting = true;
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}