Looper和Handler

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本文转自：http://hubingforever.blog.163.com/blog/static/171040579201162034730266/

Looper用于在android线程中进行消息处理，默认情况下,一个线程并不和任何Looper绑定。当我们调用Looper.prepare()时，如果当前线程还没有和任何Looper绑定，那么将创建一个Looper让它和当前线程绑定。当我们调用Looper.loop()时，它将对当前线程所对应的Looper的消息进行处理，从消息队列里取消息，处理消息，一直循环直到对该Looper调用quit（）函数。

注意：Looper.loop()中是个while循环，只有对它所在线程的Looper调用了quit()函数，Looper.loop()函数才能完成，其后的代码才能得以运行。一个线程对应一个Looper，一个Looper对应一个消息队列MessageQueue。

对于Handler，其实只是把消息发送到其对应的Looper的消息队列MessageQueue中，最后的处理还是在Looper.loop()的while循环中进行的。一个Looper可以用于构造多个Handler。因为Looper.loop()函数是个while循环，会让当前线程一直在那里处理进行循环，直到对该线程的Looper调用了quit()函数，所以，如果想对该Handler发送消息或添加Runnable以进行事务处理，要么在别的线程中进行，要么在该Handler在处理消息时或在Runnable（）的run()函数中进行事务处理时进行。

注意1：Handler的构造函数Handler()和Handler(Handler.Callback callback)，虽然没有Looper参数，但是它实际上是通过Looper.myLooper()来获取当前线程中的Looper的。

注意2：如果你使用的Looper来自于你自己创建的线程，那么在不使用其对应的Handler时候，一定要通过handler.getLooper().quit()来使其线程退出。

以下是Android API中的一个典型的Looper thread实现

示例1：

class LooperThread extends Thread

{

public Handler mHandler;

public void run()

{

Looper.prepare();

mHandler = new Handler()

{

public void handleMessage(Message msg)

{

// process incoming messages here

}

};

Looper.loop();

}

注意：默认情况下，线程是没有Looper的，所以要调用 Looper.prepare()来给线程创建消息循环，然后再通过，Looper.loop()来使消息循环起作用。

另外，Activity的MainUI线程已经新建并绑定了个Looper(在源码1的，Main函数中你可以看到)。所以在Activity中新建Handler时，不需要先调用Looper.prepare()。

关于Activity的MainUI线程的更多内容可以查看源码文件ActivityThread.java,它位于android\frameworks\base\core\java\android\app下

源码1

public final class ActivityThread {

//省略

final ApplicationThread mAppThread = new ApplicationThread();

final Looper mLooper = Looper.myLooper();

final H mH = new H();

//省略

private final class H extends Handler {

//省略

}

//省略

public static final void main(String[] args) {

SamplingProfilerIntegration.start();

Process.setArgV0("<pre-initialized>");

Looper.prepareMainLooper();

if (sMainThreadHandler == null) {

sMainThreadHandler = new Handler();

}

ActivityThread thread = new ActivityThread();

thread.attach(false);

if (false) {

Looper.myLooper().setMessageLogging(new

LogPrinter(Log.DEBUG, "ActivityThread"));

}

Looper.loop();

if (Process.supportsProcesses()) {

throw new RuntimeException("Main thread loop unexpectedly exited");

}

thread.detach();

String name = (thread.mInitialApplication != null)

? thread.mInitialApplication.getPackageName()

: "<unknown>";

Slog.i(TAG, "Main thread of " + name + " is now exiting");

}

还Activity的生命周期函数（如onCreate(),onResume）本身也是通过一个基于其MainUI线程的Looper（即ActivityThread的Main函数线程）的Handler（即ActivityThread的H mH这个Handler）来调用的.也就说这些函数都是在Looper.loop()中被执行的。当然如果我们创建了一个基于Activity本身的MainUI线程的Looper的Handler的话，该Handler的事务处理也是在Looper.loop()中进行的。我们从测试实例1也可以看到这一点。

测试实例1：

package com.teleca.robin;

import android.app.Activity;

import android.os.Bundle;

import android.os.Handler;

import android.util.Log;

public class MainActivity extends Activity {

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

Log.i(tag,"-----------------------------------------------");

StackTraceElement st[]= Thread.currentThread().getStackTrace();

for(int i=0;i<st.length;i++)

Log.i(tag,i+":"+st[i]);

Log.i(tag,"------------------------------------------------");

handler=new Handler();

handler.postDelayed(r, 100);

handler2.postDelayed(r, 200);

}

final static String tag="robin";

Handler handler;

Handler handler2=new Handler();

Runnable r=new Runnable(){

public void run()

{

StackTraceElement st[]= Thread.currentThread().getStackTrace();

for(int i=0;i<st.length;i++)

Log.i(tag,i+":"+st[i]);

Log.i(tag,"----------------------------------------------");

}

};

}

测试结果：

07-20 22:10:18.799: INFO/robin(7844): -----------------------------------------------

07-20 22:10:18.819: INFO/robin(7844): 0:dalvik.system.VMStack.getThreadStackTrace(Native Method)

07-20 22:10:18.819: INFO/robin(7844): 1:java.lang.Thread.getStackTrace(Thread.java:788)

07-20 22:10:18.819: INFO/robin(7844): 2:com.teleca.robin.MainActivity.onCreate(MainActivity.java:15)

07-20 22:10:18.819: INFO/robin(7844): 3:android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)

07-20 22:10:18.819: INFO/robin(7844): 4:android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2633)

07-20 22:10:18.819: INFO/robin(7844): 5:android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2685)

07-20 22:10:18.819: INFO/robin(7844): 6:android.app.ActivityThread.access$2300(ActivityThread.java:126)

07-20 22:10:18.819: INFO/robin(7844): 7:android.app.ActivityThread$H.handleMessage(ActivityThread.java:2038)

07-20 22:10:18.819: INFO/robin(7844): 8:android.os.Handler.dispatchMessage(Handler.java:99)

07-20 22:10:18.819: INFO/robin(7844): 9:android.os.Looper.loop(Looper.java:123)

07-20 22:10:18.819: INFO/robin(7844): 10:android.app.ActivityThread.main(ActivityThread.java:4633)

07-20 22:10:18.819: INFO/robin(7844): 11:java.lang.reflect.Method.invokeNative(Native Method)

07-20 22:10:18.819: INFO/robin(7844): 12:java.lang.reflect.Method.invoke(Method.java:521)

07-20 22:10:18.819: INFO/robin(7844): 13:com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)

07-20 22:10:18.819: INFO/robin(7844): 14:com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

07-20 22:10:18.819: INFO/robin(7844): 15:dalvik.system.NativeStart.main(Native Method)

07-20 22:10:18.819: INFO/robin(7844): ------------------------------------------------

07-20 22:10:18.969: INFO/robin(7844): 0:dalvik.system.VMStack.getThreadStackTrace(Native Method)

07-20 22:10:18.969: INFO/robin(7844): 1:java.lang.Thread.getStackTrace(Thread.java:788)

07-20 22:10:18.969: INFO/robin(7844): 2:com.teleca.robin.MainActivity$1.run(MainActivity.java:29)

07-20 22:10:18.969: INFO/robin(7844): 3:android.os.Handler.handleCallback(Handler.java:587)

07-20 22:10:18.969: INFO/robin(7844): 4:android.os.Handler.dispatchMessage(Handler.java:92)

07-20 22:10:18.969: INFO/robin(7844): 5:android.os.Looper.loop(Looper.java:123)

07-20 22:10:18.969: INFO/robin(7844): 6:android.app.ActivityThread.main(ActivityThread.java:4633)

07-20 22:10:18.969: INFO/robin(7844): 7:java.lang.reflect.Method.invokeNative(Native Method)

07-20 22:10:18.969: INFO/robin(7844): 8:java.lang.reflect.Method.invoke(Method.java:521)

07-20 22:10:18.969: INFO/robin(7844): 9:com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)

07-20 22:10:18.969: INFO/robin(7844): 10:com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

07-20 22:10:18.969: INFO/robin(7844): 11:dalvik.system.NativeStart.main(Native Method)

07-20 22:10:18.969: INFO/robin(7844): ----------------------------------------------

07-20 22:10:19.019: INFO/robin(7844): 0:dalvik.system.VMStack.getThreadStackTrace(Native Method)

07-20 22:10:19.019: INFO/robin(7844): 1:java.lang.Thread.getStackTrace(Thread.java:788)

07-20 22:10:19.019: INFO/robin(7844): 2:com.teleca.robin.MainActivity$1.run(MainActivity.java:29)

07-20 22:10:19.019: INFO/robin(7844): 3:android.os.Handler.handleCallback(Handler.java:587)

07-20 22:10:19.019: INFO/robin(7844): 4:android.os.Handler.dispatchMessage(Handler.java:92)

07-20 22:10:19.019: INFO/robin(7844): 5:android.os.Looper.loop(Looper.java:123)

07-20 22:10:19.019: INFO/robin(7844): 6:android.app.ActivityThread.main(ActivityThread.java:4633)

07-20 22:10:19.019: INFO/robin(7844): 7:java.lang.reflect.Method.invokeNative(Native Method)

07-20 22:10:19.019: INFO/robin(7844): 8:java.lang.reflect.Method.invoke(Method.java:521)

07-20 22:10:19.019: INFO/robin(7844): 9:com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)

07-20 22:10:19.019: INFO/robin(7844): 10:com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

07-20 22:10:19.019: INFO/robin(7844): 11:dalvik.system.NativeStart.main(Native Method)

07-20 22:10:19.019: INFO/robin(7844): ----------------------------------------------

另外同过查看ActivityThread.java源码，你可以看到系统还会通过ApplicationThread mAppThread向该Handler发送消息，以便进行事务处理。

测试实例2

文件 MyService.java

package com.lenovo.robin.test;

import android.app.Service;

import android.content.Intent;

import android.os.IBinder;

import android.util.Log;

public class MyService extends Service {

String tag="robin";

@Override

public void onCreate() {

Log.i(tag,"MyService is oncreate");

}

@Override

public int onStartCommand(Intent intent, int flags, int startId) {

StackTraceElement st[]= Thread.currentThread().getStackTrace();

for(int i=0;i<st.length;i++)

Log.i(tag,i+":"+st[i]);

return START_STICKY;

}

@Override

public void onDestroy() {

Log.i(tag,"OnDestory");

}

@Override

public IBinder onBind(Intent arg0) {

return null;

}

测试结果

08-12 22:11:30.950: I/robin(26133): MyService is oncreate

08-12 22:11:30.960: I/robin(26133): 0:dalvik.system.VMStack.getThreadStackTrace(Native Method)

08-12 22:11:30.960: I/robin(26133): 1:java.lang.Thread.getStackTrace(Thread.java:745)

08-12 22:11:30.960: I/robin(26133): 2:com.lenovo.robin.test.MyService.onStartCommand(MyService.java:18)

08-12 22:11:30.960: I/robin(26133): 3:android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2456)

08-12 22:11:30.960: I/robin(26133): 4:android.app.ActivityThread.access$2800(ActivityThread.java:135)

08-12 22:11:30.960: I/robin(26133): 5:android.app.ActivityThread$H.handleMessage(ActivityThread.java:1127)

08-12 22:11:30.960: I/robin(26133): 6:android.os.Handler.dispatchMessage(Handler.java:99)

08-12 22:11:30.960: I/robin(26133): 7:android.os.Looper.loop(Looper.java:150)

08-12 22:11:30.960: I/robin(26133): 8:android.app.ActivityThread.main(ActivityThread.java:4385)

08-12 22:11:30.960: I/robin(26133): 9:java.lang.reflect.Method.invokeNative(Native Method)

08-12 22:11:30.960: I/robin(26133): 10:java.lang.reflect.Method.invoke(Method.java:507)

08-12 22:11:30.960: I/robin(26133): 11:com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:849)

08-12 22:11:30.970: I/robin(26133): 12:com.android.internal.os.ZygoteInit.main(ZygoteInit.java:607)

08-12 22:11:30.970: I/robin(26133): 13:dalvik.system.NativeStart.main(Native Method)

测试实例3

文件MainActivity.java

package com.lenovo.robin.test;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.support.v4.app.NavUtils;
public class MainActivity extends Activity {
 static boolean iscreated=false;
 final static String TAG="robin";
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        iscreated=true;
        Log.i(TAG,"on create() in MainActivity");
        this.startService(new Intent(this,MyService.class));
    }
    @Override
    public void onDestroy() {
        Log.i(TAG,"OnDestoryv in main");
        super.onDestroy();
        android.os.Process.killProcess(android.os.Process.myPid());
        //System.exit(1);
    }
    public void onClick(View v)
    {
     StackTraceElement st[]= Thread.currentThread().getStackTrace();
     for(int i=0;i<st.length&&i<20;i++)
      Log.w(TAG,i+":"+st[i]);
    }
}

文件layout\activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >
    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:text="@string/hello_world"
        tools:context=".MainActivity" />
    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_above="@+id/textView1"
        android:layout_alignLeft="@+id/textView1"
        android:layout_marginBottom="46dp"
        android:layout_marginLeft="44dp"
        android:text="Button" 
        android:onClick="onClick"/>
</RelativeLayout>

运行结果：

08-17 08:22:36.755: W/robin(12413): 0:dalvik.system.VMStack.getThreadStackTrace(Native Method)

08-17 08:22:36.755: W/robin(12413): 1:java.lang.Thread.getStackTrace(Thread.java:745)

08-17 08:22:36.755: W/robin(12413): 2:com.lenovo.robin.test.MainActivity.onClick(MainActivity.java:32)

08-17 08:22:36.755: W/robin(12413): 3:java.lang.reflect.Method.invokeNative(Native Method)

08-17 08:22:36.755: W/robin(12413): 4:java.lang.reflect.Method.invoke(Method.java:507)

08-17 08:22:36.755: W/robin(12413): 5:android.view.View$1.onClick(View.java:2187)

08-17 08:22:36.755: W/robin(12413): 6:android.view.View.performClick(View.java:2533)

08-17 08:22:36.755: W/robin(12413): 7:android.view.View$PerformClick.run(View.java:9320)

08-17 08:22:36.755: W/robin(12413): 8:android.os.Handler.handleCallback(Handler.java:587)

08-17 08:22:36.755: W/robin(12413): 9:android.os.Handler.dispatchMessage(Handler.java:92)

08-17 08:22:36.755: W/robin(12413): 10:android.os.Looper.loop(Looper.java:150)

08-17 08:22:36.755: W/robin(12413): 11:android.app.ActivityThread.main(ActivityThread.java:4385)

08-17 08:22:36.755: W/robin(12413): 12:java.lang.reflect.Method.invokeNative(Native Method)

08-17 08:22:36.755: W/robin(12413): 13:java.lang.reflect.Method.invoke(Method.java:507)

08-17 08:22:36.755: W/robin(12413): 14:com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:849)

08-17 08:22:36.765: W/robin(12413): 15:com.android.internal.os.ZygoteInit.main(ZygoteInit.java:607)

08-17 08:22:36.765: W/robin(12413): 16:dalvik.system.NativeStart.main(Native Method)