Looper和Handler如何改写成一个长尾词？

2026-04-12 01:091阅读0评论SEO基础

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Looper 用于在 Android 线程中处理消息，默认情况下，一个线程不会有任何 Looper 绑定。当调用 Looper.prepare() 时，如果当前线程尚未与任何 Looper 绑定，系统将创建一个新的 Looper 并将其与线程绑定。

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,"----------------------------------------------"); } }; } ： 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 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 = "schemas.android.com/apk/res/android" xmlns:tools = "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:

标签：Looper 和 handler 用于在