handler机制详解

时间：2015-01-31 01:39:02 收藏：0 阅读：247

2015年1月30日 13:51:32 晴

handler机制详解

handler机制

一个Activity启动的时候，先是ActivityManager先为每一个application创建一个ActivityThread，然后调用ActivityThread里面的main方法，其中有一个代码

Looper.prepareMainLooper();

而Looper类中 Looper.prepareMainLooper();方法调用的是

public static final void prepare() {

if (sThreadLocal.get() != null) {

throw new RuntimeException("Only one Looper may be created per thread");

}

sThreadLocal.set(new Looper());

}

从线程级共享对象中设置一个looper对象，如果这个对象已经被创建过，则抛出异常

回到ActivityThread接着看它的main方法

接下来有一行代码

Looper.loop();

Looper类中

public static final void loop() {

Looper me = myLooper();

MessageQueue queue = me.mQueue;

while (true) {

Message msg = queue.next(); // might block

//if (!me.mRun) {

// break;

//}

if (msg != null) {

if (msg.target == null) {

// No target is a magic identifier for the quit message.

return;

}

if (me.mLogging!= null) me.mLogging.println(

">>>>> Dispatching to " + msg.target + " "

+ msg.callback + ": " + msg.what

);

msg.target.dispatchMessage(msg);

if (me.mLogging!= null) me.mLogging.println(

"<<<<< Finished to " + msg.target + " "

+ msg.callback);

msg.recycle();

}

}

}

说明一个application应用中，主线程ActivityThread一直存在一个looper死循环，
处理界面更新和activity生命周期及service等操作

还是看它的第一行
Looper me = myLooper();

看看myLooper();

public static final Looper myLooper() {

return (Looper)sThreadLocal.get();

}

从线程级共享对象中获取Looper.prepareMainLooper()
存入的looper对象，而且因为上面的一个判断，所以每个界面取出来的looper都是相同的；

这里实现了多个Activity取得都是同一个Looper
主线程ActivityThread中还有一个点就是它的handler是它自己自定义的

private final class H extends Handler {

public static final int LAUNCH_ACTIVITY = 100;

public static final int PAUSE_ACTIVITY = 101;

public static final int PAUSE_ACTIVITY_FINISHING= 102;

public static final int STOP_ACTIVITY_SHOW = 103;

public static final int STOP_ACTIVITY_HIDE = 104;

public static final int SHOW_WINDOW = 105;

public static final int HIDE_WINDOW = 106;

public static final int RESUME_ACTIVITY = 107;

public static final int SEND_RESULT = 108;

public static final int DESTROY_ACTIVITY = 109;

public static final int BIND_APPLICATION = 110;

public static final int EXIT_APPLICATION = 111;

public static final int NEW_INTENT = 112;

public static final int RECEIVER = 113;

public static final int CREATE_SERVICE = 114;

public static final int SERVICE_ARGS = 115;

public static final int STOP_SERVICE = 116;

public static final int REQUEST_THUMBNAIL = 117;

public static final int CONFIGURATION_CHANGED = 118;

public static final int CLEAN_UP_CONTEXT = 119;

public static final int GC_WHEN_IDLE = 120;

public static final int BIND_SERVICE = 121;

public static final int UNBIND_SERVICE = 122;

public static final int DUMP_SERVICE = 123;

public static final int LOW_MEMORY = 124;

public static final int ACTIVITY_CONFIGURATION_CHANGED = 125;

public static final int RELAUNCH_ACTIVITY = 126;

public static final int PROFILER_CONTROL = 127;

public static final int CREATE_BACKUP_AGENT = 128;

public static final int DESTROY_BACKUP_AGENT = 129;

public static final int SUICIDE = 130;

public static final int REMOVE_PROVIDER = 131;

public static final int ENABLE_JIT = 132;

public static final int DISPATCH_PACKAGE_BROADCAST = 133;

public static final int SCHEDULE_CRASH = 134;

我们可以看懂很多的状态，当状态改变时发送不同Message的H消息，从而进行相应的处理

先ActivityThread被ActivityManager创建，然往ThreadLocal里面存一个创建的Looper，接下来执行Loop 一直阻塞操作更新UI和生命周期，用户点击后发消息