anr,多线程,handler

应该了解的知识：1.什么是进程、什么是线程2.为什么要使用多线程3.Handler机制4.Handler原理什么是进程、什么是线程进程是一个程序的完全执行，包括了程序和程序需要的资源，是分配资源的基本单位；线程是独立运行和独立调度的基本单位，一边听歌一边打字一边玩游戏看似是同时进行实际上是CPU运行时候，快速切换资源，让用户感觉是同时进行的，我们可以将线程理解为程序中的一段可执行的代码块。为什么要使用多线程--》可以参考别人的专门理解的理解：http://blog.csdn.net/itjavawfc/article/details/50360776 1）耗时的操作使用线程，提高应用程序响应2）并行操作时使用线程，如C/S架构的服务器端并发线程响应用户的请求。3）多CPU系统中，使用线程提高CPU利用率4）改善程序结构。一个既长又复杂的进程可以考虑分为多个线程，成为几个独立或半独立的运行部分，这样的程序会利于理解和修改。 Handler 讲解先看handler源码的部分解释：

/**
* A Handler allows you to send and process {@link Message} and Runnable
* objects associated with a thread's {@link MessageQueue}.  Each Handler
* instance is associated with a single thread and that thread's message
* queue.  When you create a new Handler, it is bound to the thread /
* message queue of the thread that is creating it -- from that point on,
* it will deliver messages and runnables to that message queue and execute
* them as they come out of the message queue.
*
* <p>There are two main uses for a Handler: (1) to schedule messages and
* runnables to be executed as some point in the future; and (2) to enqueue
* an action to be performed on a different thread than your own.
*
* <p>Scheduling messages is accomplished with the
* {@link #post}, {@link #postAtTime(Runnable, long)},
* {@link #postDelayed}, {@link #sendEmptyMessage},
* {@link #sendMessage}, {@link #sendMessageAtTime}, and
* {@link #sendMessageDelayed} methods.  The <em>post</em> versions allow
* you to enqueue Runnable objects to be called by the message queue when
* they are received; the <em>sendMessage</em> versions allow you to enqueue
* a {@link Message} object containing a bundle of data that will be
* processed by the Handler's {@link #handleMessage} method (requiring that
* you implement a subclass of Handler).
*
* <p>When posting or sending to a Handler, you can either
* allow the item to be processed as soon as the message queue is ready
* to do so, or specify a delay before it gets processed or absolute time for
* it to be processed.  The latter two allow you to implement timeouts,
* ticks, and other timing-based behavior.
*
* <p>When a
* process is created for your application, its main thread is dedicated to
* running a message queue that takes care of managing the top-level
* application objects (activities, broadcast receivers, etc) and any windows
* they create.  You can create your own threads, and communicate back with
* the main application thread through a Handler.  This is done by calling
* the same <em>post</em> or <em>sendMessage</em> methods as before, but from
* your new thread.  The given Runnable or Message will then be scheduled
* in the Handler's message queue and processed when appropriate.
*/

提取信息时：Handler是用来发送并处理消息和runnable线程对象的，同时2）排列一个在不同的线程上执行的操作，而不是自己的。Handler的原理实际上就是说Android中异步线程的实现原理：                                                                在线程内部有一个或多个Handler对象，外部程序通过改Handler对象向线程发送异步消息，消息经由Handler传递道MessageQueue对象中。线程内部智能包含一个MessageQueue对象，Looper对象像一个抽水机一样，不断的读取线程MessageQueue中的消息，并回掉给Handler对象中的回掉函数handlerMessage().分析线程内部的Handler、MessageQueue/Looper类的调用过程1）.线程局部存储Thread Local Storage程序员通过调用Looper类的静态方法prepare（）为线程创建MessageQueue对象：看源码

/**Initialize the current thread as a looper.
* This gives you a chance to create handlers that then reference
* this looper, before actually starting the loop. Be sure to call
* {@link #loop()} after calling this method, and end it by calling
* {@link #quit()}.
*/
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))
}

我们在看看Looper(quitAllowed)源码：

/**
*Return the {@link MessageQueue} object associated with the current
* thread.  This must be called from a thread running a Looper, or a
* NullPointerException will be thrown.
*/
public static @NonNull MessageQueue myQueue() {
return myLooper().mQueue;
}

private Looper(boolean quitAllowed) {
mQueue = new MessageQueue(quitAllowed);
mThread = Thread.currentThread();
}

可以看到我们通过上面代码创建了Message对象。     上面的sThreadLocal的类型是ThreadLocal,该类的作用是提供“线程局部存储”也叫线程本地变量.我们希望，当同时从一个线程中引用该变量时，其值总是相同的，不同线程引用该变量的时候，其值是不同的，即我们需要一个作用域为线程的变量的定义，这就是线程变量局部存储。     ThreadLocal就是提供了这种功能的类，Looper内部的sThreadLocal变量是当该进程第一次调用Looper.prepare()时候被复制的，之后该进程中的其它线程调用prepare（）函数的时候，sThreadLocak变量就已经被赋值了。sThreadLocak对象内部会根据调用prepare()线程的id保存一个数据对象，这个数据对象就是所谓的“线程局部存储”对象，该对象是通过sThreadLocal的set()方法设置进去的，Looper类保存的这个对象是一个Looper对象。   prepare()函数中首先调用sThreadLocal.get（）函数获取该县城对应的Looper对象，如果线程已经存在Looper对象，肯定出错。否则为该线程创建一个新的Looper对象。   为什么一个线程中只能有一个Looper对象呢？因为异步线程需要的，每个Looper对象都会定义一个MessageQueue对象，一个异步线程只能有一个消息队列，所有只有一个Looper对象。    讲那么多理论的东西可能都绕地球好多圈了，不太理解：其实在一个线程中的Looper对象创建MessageQueue中的过程中即执行Looper.praper（）方法的时候，使用sThreadLocal来找该设置Looper对象到线程中去，通过线程的id设置道sThreadLoad对象中去。一个线程中就只有一个Looper对象了。prepare()首先调用sThreadLocal().get()获得该线程的Looperd对象.若果存在直接报异常，不存在直接创建，这样保证每个线程只有一个Looper对象和MessageQueue对象.Looper      Looper作用：第一、为该类的静态函数prepare()线程创建一个消息队列；第二、提供静态函数loop()，使调用该函数线程进行无线循环，并从消息队列中读取消息。第一点就是上面的sThreadLocal中的相关代码创建MessageQueue对象。     当需要一个线程变为异步消息处理线程的时候，在Thread类的run方法调用Looper.prepare()为该线程创建一个MessageQueue对象，在调用Looper.loop（）函数，进行消息处理循环：

/**
* Run the message queue in this thread. Be sure to call
* {@link #quit()} to end the loop.
*/
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();
}
}

该方法的解释：

Run the message queue in this thread. Be sure to call

就是返回线程中的消息队列，并回掉！获得Looper对象finalLooper me =myLooper();其实通过sThreadLocal()调用获得

/**
* Return the Looper object associated with the current thread.  Returns
* null if the calling thread is not associated with a Looper.
*/
public static @Nullable Looper myLooper() {
return sThreadLocal.get();
}

进入无线循环while(true):

for (;;) {
Message msg = queue.next(); // might block
if (msg == null) {
// No message indicates that the message queue is quitting.
return;
}

可以看看next()，当message为空，则线程挂起。msg.target.dispatchMessage()，完成消息的处理。

msg.target.dispatchMessage(msg);要看看里面的源码：

/**
* Handle system messages here.
*/
public void dispatchMessage(Message msg) {
if (msg.callback != null) {
handleCallback(msg);
} else {
if (mCallback != null) {
if (mCallback.handleMessage(msg)) {
return;
}
}
handleMessage(msg);
}
}

处理完消息后ong

msg.recycleUnchecked();回收Message对象占用的系统资源。

MessageQueue消息队列：消息读/取不能同时进行，有枷锁机制/*** Low-level class holding the list of messages to be dispatched by a* {@link Looper}. Messages are not added directly to a MessageQueue,* but rather through {@link Handler} objects associated with the Looper.** <p>You can retrieve the MessageQueue for the current thread with* {@link Looper#myQueue() Looper.myQueue()}.*/public final class MessageQueue {看源码：保存message的list【容器】,message不是直接添加道MessageQueue中取，通过looper对象来的。Handler：在Looper.looper（）中取出消息后，回掉msg.target对象的handleMessage()添加函数，而msg.target的类型正是handler。Handler处理消息地方：/*** Handle system messages here.*/public void dispatchMessage(Message msg) {if (msg.callback != null) {handleCallback(msg);} else {if (mCallback != null) {if (mCallback.handleMessage(msg)) {return;}}handleMessage(msg);}}实际项目中的运用：三点要理解第一种方式：先：重写创建handler对象，重写handler的handler的handlerMessage（）方法private Handler handler = new Handler(){public void handleMessage(Message msg) {//消息接收到了int what = msg.what;switch (what) {case 1:String text = (String) msg.obj;ts.setText(text);break;case 2://刷新其他UIbreak;default:break;}};};其次创建消息：Message msg = new Message();//初始化方式msg_ob.obj = "你家的牛在我菜园吃菜";msg_ob.what = 1;//企业开发用常量

handler.sendMessage(msg);

下面是否封装的一个HandlerUtils工具:

public class MsgUtils {static public void SendMSG(Handler handler,Object obj,int what,int arg1){Message msg = new Message();msg.obj = obj;msg.what = what;msg.arg1 = arg1;handler.sendMessage(msg);}static public void SendMSG(Handler handler,Object obj,int what){Message msg = new Message();msg.obj = obj;msg.what = what;handler.sendMessage(msg);}static public void SendMSG(Handler handler,int what){Message msg = new Message();msg.what = what;handler.sendMessage(msg);}static public void SendMSG(Handler handler,int what,int arg1){Message msg = new Message();msg.what = what;msg.arg1 = arg1;handler.sendMessage(msg);}static public void SendMSG(Handler handler,Object obj){Message msg = new Message();msg.obj = obj;handler.sendMessage(msg);}static public void SendMSG(Handler handler,int what,Object obj,int arg1){Message msg = new Message();msg.obj = obj;msg.arg1 = arg1;msg.what = what;handler.sendMessage(msg);}}

第二种方式：获取message消息方式不一样Message msg_ob = handler.obtainMessage();//使用了池的概念msg_ob.obj = "你家的牛在我菜园吃菜";msg_ob.what = 1;//企业开发用常量msg_ob.sendToTarget();直接通过handler的obtainMessage（）方法使用了池的概念源码如下：/*** Returns a new {@link android.os.Message Message} from the global message pool. More efficient than* creating and allocating new instances. The retrieved message has its handler set to this instance (Message.target == this).* If you don't want that facility, just call Message.obtain() instead.*/public final Message obtainMessage(){return Message.obtain(this);}

    /*** Same as {@link #obtainMessage()}, except that it also sets the what member of the returned Message.** @param what Value to assign to the returned Message.what field.* @return A Message from the global message pool.*/public final Message obtainMessage(int what){return Message.obtain(this, what);}

/*** Same as {@link #obtain()}, but sets the value for the <em>target</em> member on the Message returned.* @param h  Handler to assign to the returned Message object's <em>target</em> member.* @return A Message object from the global pool.*/public static Message obtain(Handler h) {Message m = obtain();m.target = h;return m;}

第三种方式，实现一个ruannable接口，然后将这个线程作为消息发送：private Runnable run_handler = new Runnable() {public void run() {i++;ts.setText("runnable 刷新UI"+i+"次");handler.postDelayed(run_handler, 100);}};这种方式的好处是随时添加删除：handler.post(run_handler);

handler.removeCallbacks(run_handler);//停止循环

 /*** Causes the Runnable r to be added to the message queue.* The runnable will be run on the thread to which this handler is* attached.** @param r The Runnable that will be executed.** @return Returns true if the Runnable was successfully placed in to the*         message queue.  Returns false on failure, usually because the*         looper processing the message queue is exiting.*/public final boolean post(Runnable r){return  sendMessageDelayed(getPostMessage(r), 0);}/*** Causes the Runnable r to be added to the message queue, to be run* at a specific time given by <var>uptimeMillis</var>.* <b>The time-base is {@link android.os.SystemClock#uptimeMillis}.</b>* Time spent in deep sleep will add an additional delay to execution.* The runnable will be run on the thread to which this handler is attached.** @param r The Runnable that will be executed.* @param uptimeMillis The absolute time at which the callback should run,*         using the {@link android.os.SystemClock#uptimeMillis} time-base.** @return Returns true if the Runnable was successfully placed in to the*         message queue.  Returns false on failure, usually because the*         looper processing the message queue is exiting.  Note that a*         result of true does not mean the Runnable will be processed -- if*         the looper is quit before the delivery time of the message*         occurs then the message will be dropped.*/public final boolean postAtTime(Runnable r, long uptimeMillis){return sendMessageAtTime(getPostMessage(r), uptimeMillis);}