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Looper和Handler  

2011-07-21 10:06:24|  分类: Android基础 |  标签: |举报 |字号 订阅

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    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()来给线程创建消息队列,然后再通过,Looper.loop()来不停(死循环)的处理消息消息队列的消失。
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
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)
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