1.1 ActivityThread工作原理?
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1.1 ActivityThread工作原理?
通过前面的学习（复习）我们知道ActivityThread其实不是一个Thread，而是一个final类型的Java类，并且拥有main(String[] args) 方法。Android原生以Java语言为基础，Java的JVM启动的入口就是main(String[] args)。
public static void main(String[] args) { Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ActivityThreadMain"); // Install selective syscall interception AndroidOs.install(); // CloseGuard defaults to true and can be quite spammy. We // disable it here, but selectively enable it later (via // StrictMode) on debug builds, but using DropBox, not logs. CloseGuard.setEnabled(false); Environment.initForCurrentUser(); // Make sure TrustedCertificateStore looks in the right place for CA certificates final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId()); TrustedCertificateStore.setDefaultUserDirectory(configDir); Process.setArgV0("<pre-initialized>"); Looper.prepareMainLooper(); // Find the value for {@link #PROC_START_SEQ_IDENT} if provided on the command line. // It will be in the format "seq=114" long startSeq = 0; if (args != null) { for (int i = args.length - 1; i >= 0; --i) { if (args[i] != null && args[i].startsWith(PROC_START_SEQ_IDENT)) { startSeq = Long.parseLong( args[i].substring(PROC_START_SEQ_IDENT.length())); } } } ActivityThread thread = new ActivityThread(); thread.attach(false, startSeq); if (sMainThreadHandler == null) { sMainThreadHandler = thread.getHandler(); } if (false) { Looper.myLooper().setMessageLogging(new LogPrinter(Log.DEBUG, "ActivityThread")); } // End of event ActivityThreadMain. Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); Looper.loop(); throw new RuntimeException("Main thread loop unexpectedly exited"); } 以上为main方法中的全部代码，我们关注以下几点：
- Looper.prepareMainLooper();
- Looper.loop();
- thread.attach(false, startSeq);
- thread.getHandler();
Looper.prepareMainLooper();
主程序Looper的初始化工作
public static void prepareMainLooper() { prepare(false); synchronized (Looper.class) { if (sMainLooper != null) { throw new IllegalStateException("The main Looper has already been prepared."); } sMainLooper = myLooper(); } } 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)); } public static @Nullable Looper myLooper() { return sThreadLocal.get(); } 可以看到new Looper的时候传了false
Looper.loop();
1.Looper就是字面意思（轮训器），在loop方法中无限循环的去MessageQueue（消息队列）中读取消息。
- MessageQueue则通过next方法无限循环的进行消息出队，无消息时则会进入睡眠
执行thread.attach(false, startSeq);
通过thread.attach(false, startSeq);把ActivityThread 和主线程进行绑定。