Handler, Loop, MessageQueue的工作原理
2015-11-27 17:05
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Message: 消息对象
Looper: 每个线程拥有一个looper,负责读取MessageQueue中的Message,然后把消息发送给发送消息的Handler处理。
MessageQueue: 消息队列,FIFO,负责管理Message。在Looper的构造器中创建,与对应的Looper关联。
Looper.prepare(): 创建Looper。
Looper.loop(): 取出MessageQueue中的消息。
实例
Looper: 每个线程拥有一个looper,负责读取MessageQueue中的Message,然后把消息发送给发送消息的Handler处理。
MessageQueue: 消息队列,FIFO,负责管理Message。在Looper的构造器中创建,与对应的Looper关联。
Looper.prepare(): 创建Looper。
public static void prepare() { prepare(true); } private static void prepare(boolean quitAllowed) { if (sThreadLocal.get() != null) { throw new RuntimeException("Only one Looper may be created per thread"); } sThreadLocal.set(new Looper(quitAllowed)); }
Looper.loop(): 取出MessageQueue中的消息。
public static void loop() { final Looper me = myLooper(); if (me == null) { throw new RuntimeException("No Looper; Looper.prepare() wasn't called on this thread."); } final MessageQueue queue = me.mQueue; // Make sure the identity of this thread is that of the local process, // and keep track of what that identity token actually is. Binder.clearCallingIdentity(); final long ident = Binder.clearCallingIdentity(); for (;;) { Message msg = queue.next(); // might block if (msg == null) { // No message indicates that the message queue is quitting. return; } // This must be in a local variable, in case a UI event sets the logger Printer logging = me.mLogging; if (logging != null) { logging.println(">>>>> Dispatching to " + msg.target + " " + msg.callback + ": " + msg.what); } msg.target.dispatchMessage(msg); if (logging != null) { logging.println("<<<<< Finished to " + msg.target + " " + msg.callback); } // Make sure that during the course of dispatching the // identity of the thread wasn't corrupted. final long newIdent = Binder.clearCallingIdentity(); if (ident != newIdent) { Log.wtf(TAG, "Thread identity changed from 0x" + Long.toHexString(ident) + " to 0x" + Long.toHexString(newIdent) + " while dispatching to " + msg.target.getClass().getName() + " " + msg.callback + " what=" + msg.what); } msg.recycleUnchecked(); } }
实例
class ChildThread extends Thread { private Handler mHandler; public void run() { Looper.prepare(); mHandler = new Handler() { handlerMessage(); }; Looper.loop(); } }
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