Android中有关Handler的使用详解
Android中有关Handler的使用(一)
一个Handler允许你发送和处理消息(Message)以及与一个线程的消息队列相关的Runnable对象。每个Handler实例都和单个线程以及该线程的消息队列有关。当你创建了一个新Handler,它就会和创建它的线程/消息队列绑定,在那以后,它就会传递消息以及runnable对象给消息队列,然后执行它们。
需要使用Handler有两大主要的原因:
(1)在将来的某个时间点调度处理消息和runnable对象;
(2)将需要执行的操作放到其他线程之中,而不是自己的;
调度处理消息是通过调用post(Runnable), postAtTime(Runnable, long), postDelayed(Runnable, long), sendEmptyMessage(int), sendMessage(Message), sendMessageAtTime(Message, long)和sendMessageDelayed(Message, long)等方法完成的。其中的post版本的方法可以让你将Runnable对象放进消息队列;sendMessage版本的方法可以让你将一个包含有bundle对象的消息对象放进消息队列,然后交由handleMessage(Message)方法处理。(这个需要你复写Handler的handleMessage方法)
【以上这段翻译自android sdk】
Handler在实际开发中是很常用的,主要是用来接收子线程发送的数据,然后主线程结合此数据来更新界面UI。
Android应用程序启动时,他会开启一个主线程(也就是UI线程),管理界面中的UI控件,进行事件派发,比如说:点击一个按钮,Android会分发事件到Button上从而来响应你的操作。但是当你需要执行一个比较耗时的操作的话,例如:进行IO操作,网络通信等等,若是执行时间超过5s,那么Android会弹出一个“经典”的ANR无响应对话框,然后提示按“Force quit”或是“Wait”。解决此类问题的方法就是:我们把一些耗时的操作放到子线程中去执行。但因为子线程涉及到UI更新,而Android主线程是线程不安全的,所以更新UI的操作只能放在主线程中执行,若是放在子线程中执行的话很会出问题。所以这时就需要一种机制:主线程可以发送“命令/任务”给子线程执行,然后子线程反馈执行结果;
!你必需要知道的:
若在主线程中实例化一个Handler对象,例如:
HandlermHandler=newHandler();
此时它并没有新派生一个线程来执行此Handler,而是将此Handler附加在主线程上,故此时若你在Handler中执行耗时操作的话,还是会弹出ANR对话框!
下面就Handler的使用举一些例子,加深理解。
1、post版本的Handler使用示例:
[java]view plaincopy
- packagecom.dxyh.test;
- importandroid.app.Activity;
- importandroid.content.Context;
- importandroid.os.Bundle;
- importandroid.os.Handler;
- importandroid.util.Log;
- importandroid.view.View;
- importandroid.view.View.OnClickListener;
- importandroid.widget.Button;
- publicclassMainActivityextendsActivity
- implementsOnClickListener{
- privatefinalstaticStringTAG="HandlerTest";
- privatefinalstaticintDELAY_TIME=1000;
- privateButtonbtnStart;
- privateButtonbtnStop;
- ContextmContext=null;
- /**Calledwhentheactivityisfirstcreated.*/
- @Override
- publicvoidonCreate(BundlesavedInstanceState){
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- mContext=this;
- Log.i(TAG,"Mainthreadid="+
- Thread.currentThread().getId());
- btnStart=(Button)findViewById(R.id.btn_start);
- btnStart.setOnClickListener(this);
- btnStop=(Button)findViewById(R.id.btn_stop);
- btnStop.setOnClickListener(this);
- }
- @Override
- publicvoidonClick(Viewview){
- switch(view.getId()){
- caseR.id.btn_start:
- mHandler.postDelayed(workRunnable,DELAY_TIME);
- break;
- caseR.id.btn_stop:
- mHandler.removeCallbacks(workRunnable);
- break;
- }
- }
- RunnableworkRunnable=newRunnable(){
- intcounter=0;
- publicvoidrun(){
- if(counter++<1){
- Log.i(TAG,"workRunnablethreadid="+
- Thread.currentThread().getId());
- mHandler.postDelayed(workRunnable,DELAY_TIME);
- }
- }
- };
- HandlermHandler=newHandler();
- }
Logcat显示如下:
说明:发现thread id是相同的,这就说明:默认情况下创建的Handler会绑定到主线程上,你不能做太耗时的操作。
Android中有关Handler的使用(二)
2、sendMessage版本的Handler的使用
这里介绍几种模型:
a、默认的Handler(消息处理队列挂在主线程上)
[java] view plain copy- packagecom.dxyh.test;
- importandroid.app.Activity;
- importandroid.os.Bundle;
- importandroid.os.Handler;
- importandroid.os.Message;
- importandroid.util.Log;
- importandroid.view.View;
- importandroid.view.View.OnClickListener;
- importandroid.widget.Button;
- publicclassMainActivityextendsActivity
- implementsOnClickListener{
- privatefinalstaticStringTAG="HandlerTest";
- privatefinalstaticintTASK_BEGIN=1;
- privatefinalstaticintTASK_1=2;
- privatefinalstaticintTASK_2=3;
- privatefinalstaticintTASK_END=4;
- privateButtonbtnStart=null;
- privateButtonbtnStop=null;
- /**Calledwhentheactivityisfirstcreated.*/
- @Override
- publicvoidonCreate(BundlesavedInstanceState){
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- btnStart=(Button)findViewById(R.id.btn_start);
- btnStart.setOnClickListener(this);
- btnStop=(Button)findViewById(R.id.btn_stop);
- btnStop.setOnClickListener(this);
- Log.i(TAG,"[M_TID:"+Thread.currentThread().getId()+"]");
- }
- HandlermHandler=newHandler(){
- //注意:在各个case后面不能做太耗时的操作,否则出现ANR对话框
- @Override
- publicvoidhandleMessage(Messagemsg){
- switch(msg.what){
- caseTASK_BEGIN:
- Log.i(TAG,"[H_TID:"+
- Thread.currentThread().getId()+"]GetTASK_BEGIN");
- break;
- caseTASK_1:
- Log.i(TAG,"[H_TID:"+
- Thread.currentThread().getId()+"]GetTASK_1");
- break;
- caseTASK_2:
- Log.i(TAG,"[H_TID:"+
- Thread.currentThread().getId()+"]GetTASK_2");
- break;
- caseTASK_END:
- Log.i(TAG,"[H_TID:"+
- Thread.currentThread().getId()+"]GetTASK_END");
- finish();
- break;
- }
- super.handleMessage(msg);
- }
- };
- publicvoidonClick(Viewview){
- switch(view.getId()){
- caseR.id.btn_start:
- //启动任务(消息只有标识,立即投递)
- mHandler.sendEmptyMessage(TASK_BEGIN);
- Log.i(TAG,"SendTASK_BEGINtohandler.");
- //开始任务1(在mHandler的消息队列中获取一个Message对象,避免重复构造)
- Messagemsg1=mHandler.obtainMessage(TASK_1);
- msg1.obj="Thisistask1";
- mHandler.sendMessage(msg1);
- Log.i(TAG,"SendTASK_1tohandler.");
- //开启任务2(和上面类似)
- Messagemsg2=Message.obtain();
- msg2.arg1=10;
- msg2.arg2=20;
- msg2.what=TASK_2;
- mHandler.sendMessage(msg2);
- Log.i(TAG,"SendTASK_2tohandler.");
- break;
- caseR.id.btn_stop:
- //结束任务(空消息体,延时2s投递)
- mHandler.sendEmptyMessageDelayed(TASK_END,2000);
- Log.i(TAG,"SendTASK_ENDtohandler.");
- break;
- }
- }
- }
运行结果:
b、消息队列仍绑定在主线程上,但在子线程中发送消息。
[java] view plain copy- packagecom.dxyh.test;
- importandroid.app.Activity;
- importandroid.os.Bundle;
- importandroid.os.Handler;
- importandroid.os.Message;
- importandroid.util.Log;
- publicclassMainActivityextendsActivity{
- privatefinalstaticStringTAG="HandlerTest";
- privatefinalstaticintTASK_BEGIN=1;
- privatefinalstaticintTASK_1=2;
- privatefinalstaticintTASK_2=3;
- privatefinalstaticintTASK_END=4;
- /**Calledwhentheactivityisfirstcreated.*/
- @Override
- publicvoidonCreate(BundlesavedInstanceState){
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- Log.i(TAG,"[M_TID:"+Thread.currentThread().getId()+"]"+
- "Thisisinmainthread.");
- workThread.start();
- }
- HandlermHandler=newHandler(){
- //注意:在各个case后面不能做太耗时的操作,否则出现ANR对话框
- @Override
- publicvoidhandleMessage(Messagemsg){
- switch(msg.what){
- caseTASK_BEGIN:
- Log.i(TAG,"[H_TID:"+
- Thread.currentThread().getId()+"]GetTASK_BEGIN");
- break;
- caseTASK_1:
- Log.i(TAG,"[H_TID:"+
- Thread.currentThread().getId()+"]GetTASK_1");
- break;
- caseTASK_2:
- Log.i(TAG,"[H_TID:"+
- Thread.currentThread().getId()+"]GetTASK_2");
- break;
- caseTASK_END:
- Log.i(TAG,"[H_TID:"+
- Thread.currentThread().getId()+"]GetTASK_END");
- finish();
- break;
- }
- super.handleMessage(msg);
- }
- };
- ThreadworkThread=newThread(){
- //你可以在run方法内做任何耗时的操作,然后将结果以消息形式投递到主线程的消息队列中
- @Override
- publicvoidrun(){
- //启动任务(消息只有标识,立即投递)
- mHandler.sendEmptyMessage(TASK_BEGIN);
- Log.i(TAG,"[S_TID:"+Thread.currentThread().getId()+"]"+
- "SendTASK_STARTtohandler.");
- //开始任务1(在mHandler的消息队列中获取一个Message对象,避免重复构造)
- Messagemsg1=mHandler.obtainMessage(TASK_1);
- msg1.obj="Thisistask1";
- mHandler.sendMessage(msg1);
- Log.i(TAG,"[S_TID:"+Thread.currentThread().getId()+"]"+
- "SendTASK_1tohandler.");
- //开启任务2(和上面类似)
- Messagemsg2=Message.obtain();
- msg2.arg1=10;
- msg2.arg2=20;
- msg2.what=TASK_2;
- mHandler.sendMessage(msg2);
- Log.i(TAG,"[S_TID:"+Thread.currentThread().getId()+"]"+
- "SendTASK_2tohandler.");
- //结束任务(空消息体,延时2s投递)
- mHandler.sendEmptyMessageDelayed(TASK_END,2000);
- Log.i(TAG,"[S_TID:"+Thread.currentThread().getId()+"]"+
- "SendTASK_ENDtohandler.");
- }
- };
- }
运行结果:
c、将消息队列绑定到子线程上,主线程只管通过Handler往子线程的消息队列中投递消息即可。
[java] view plain copy- packagecom.dxyh.test;
- importandroid.app.Activity;
- importandroid.os.Bundle;
- importandroid.os.Handler;
- importandroid.os.HandlerThread;
- importandroid.os.Looper;
- importandroid.os.Message;
- importandroid.util.Log;
- publicclassMainActivityextendsActivity{
- privatefinalstaticStringTAG="HandlerTest";
- privatefinalstaticintTASK_BEGIN=1;
- privatefinalstaticintTASK_1=2;
- privatefinalstaticintTASK_2=3;
- privatefinalstaticintTASK_END=4;
- privateMyHandlermHandler=null;
- /**Calledwhentheactivityisfirstcreated.*/
- @Override
- publicvoidonCreate(BundlesavedInstanceState){
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- Log.i(TAG,"[M_TID:"+Thread.currentThread().getId()+"]"+
- "Thisisinmainthread.");
- HandlerThreadmyLooperThread=newHandlerThread("mylooperthread");
- myLooperThread.start();
- Looperlooper=myLooperThread.getLooper();
- mHandler=newMyHandler(looper);
- //启动任务(消息只有标识,立即投递)
- mHandler.sendEmptyMessage(TASK_BEGIN);
- Log.i(TAG,"[S_ID:"+Thread.currentThread().getId()+"]"+
- "SendTASK_STARTtohandler.");
- //开始任务1(在mHandler的消息队列中获取一个Message对象,避免重复构造)
- Messagemsg1=mHandler.obtainMessage(TASK_1);
- msg1.obj="Thisistask1";
- mHandler.sendMessage(msg1);
- Log.i(TAG,"[S_ID:"+Thread.currentThread().getId()+"]"+
- "SendTASK_1tohandler.");
- //开启任务2(和上面类似)
- Messagemsg2=Message.obtain();
- msg2.arg1=10;
- msg2.arg2=20;
- msg2.what=TASK_2;
- mHandler.sendMessage(msg2);
- Log.i(TAG,"[S_ID:"+Thread.currentThread().getId()+"]"+
- "SendTASK_2tohandler.");
- //结束任务(空消息体,延时2s投递)
- mHandler.sendEmptyMessageDelayed(TASK_END,2000);
- Log.i(TAG,"[S_ID:"+Thread.currentThread().getId()+"]"+
- "SendTASK_ENDtohandler.");
- }
- classMyHandlerextendsHandler{
- publicMyHandler(Looperlooper){
- super(looper);
- }
- //现在在每个case之后,你可以做任何耗时的操作了
- @Override
- publicvoidhandleMessage(Messagemsg){
- switch(msg.what){
- caseTASK_BEGIN:
- Log.i(TAG,"[H_TID:"+
- Thread.currentThread().getId()+"]GetTASK_BEGIN");
- break;
- caseTASK_1:
- Log.i(TAG,"[H_TID:"+
- Thread.currentThread().getId()+"]GetTASK_1");
- break;
- caseTASK_2:
- Log.i(TAG,"[H_TID:"+
- Thread.currentThread().getId()+"]GetTASK_2");
- break;
- caseTASK_END:
- Log.i(TAG,"[H_TID:"+
- Thread.currentThread().getId()+"]GetTASK_END");
- finish();
- break;
- }
- super.handleMessage(msg);
- }
- }
- }
运行结果:
Android中有关Handler的使用(三)
d、自己创建新的线程,然后在新线程中创建Looper,主线程调用子线程中的发消息方法,将消息发给子线程的消息队列。
[java] view plain copy
- packagecom.dxyh.test;
- importandroid.app.Activity;
- importandroid.os.Bundle;
- importandroid.os.Handler;
- importandroid.os.Looper;
- importandroid.os.Message;
- importandroid.util.Log;
- publicclassMainActivityextendsActivity{
- privatefinalstaticStringTAG="HandlerTest";
- privatefinalstaticintTASK_BEGIN=1;
- privatefinalstaticintTASK_1=2;
- privatefinalstaticintTASK_2=3;
- privatefinalstaticintTASK_END=4;
- privateHandlerworkHandler=null;
- /**Calledwhentheactivityisfirstcreated.*/
- @Override
- publicvoidonCreate(BundlesavedInstanceState){
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- Log.i(TAG,"[M_TID:"+Thread.currentThread().getId()+"]"+
- "Thisisinmainthread.");
- LooperThreadtestThread=newLooperThread();
- testThread.start();
- //注意,这里需要等待一下,防止出现空指针异常
- while(null==workHandler){
- }
- testThread.sendMessageTodoYourWork();
- }
- classLooperThreadextendsThread{
- @Override
- publicvoidrun(){
- Looper.prepare();
- workHandler=newHandler(){
- //现在在每个case之后,你可以做任何耗时的操作了
- @Override
- publicvoidhandleMessage(Messagemsg){
- switch(msg.what){
- caseTASK_BEGIN:
- Log.i(TAG,"[H_TID:"+
- Thread.currentThread().getId()+"]GetTASK_BEGIN");
- break;
- caseTASK_1:
- Log.i(TAG,"[H_TID:"+
- Thread.currentThread().getId()+"]GetTASK_1");
- break;
- caseTASK_2:
- Log.i(TAG,"[H_TID:"+
- Thread.currentThread().getId()+"]GetTASK_2");
- break;
- caseTASK_END:
- Log.i(TAG,"[H_TID:"+
- Thread.currentThread().getId()+"]GetTASK_END");
- Looper.myLooper().quit();
- finish();
- break;
- }
- super.handleMessage(msg);
- }
- };
- Looper.loop();
- }
- publicvoidsendMessageTodoYourWork(){
- Log.i(TAG,"[S_ID:"+Thread.currentThread().getId()+"]"+
- "SendTASK_STARTtohandler.");
- //启动任务(消息只有标识,立即投递)
- workHandler.sendEmptyMessage(TASK_BEGIN);
- Log.i(TAG,"[S_ID:"+Thread.currentThread().getId()+"]"+
- "SendTASK_1tohandler.");
- //开始任务1(在workHandler的消息队列中获取一个Message对象,避免重复构造)
- Messagemsg1=workHandler.obtainMessage(TASK_1);
- msg1.obj="Thisistask1";
- workHandler.sendMessage(msg1);
- Log.i(TAG,"[S_ID:"+Thread.currentThread().getId()+"]"+
- "SendTASK_2tohandler.");
- //开启任务2(和上面类似)
- Messagemsg2=Message.obtain();
- msg2.arg1=10;
- msg2.arg2=20;
- msg2.what=TASK_2;
- workHandler.sendMessage(msg2);
- Log.i(TAG,"[S_ID:"+Thread.currentThread().getId()+"]"+
- "SendTASK_ENDtohandler.");
- //结束任务(空消息体,延时2s投递)
- workHandler.sendEmptyMessageDelayed(TASK_END,2000);
- }
- }
- }
运行结果:
e、主/子线程均有一个消息队列,然后相互传递消息(这种方式是最灵活的,双向传递,也不复杂)
[java] view plain copy
- packagecom.dxyh.test;
- importandroid.app.Activity;
- importandroid.os.Bundle;
- importandroid.os.Handler;
- importandroid.os.Looper;
- importandroid.os.Message;
- importandroid.util.Log;
- publicclassMainActivityextendsActivity{
- privatefinalstaticStringTAG="HandlerTest";
- privatefinalstaticintTASK_BEGIN=1;
- privatefinalstaticintTASK_1=2;
- privatefinalstaticintTASK_2=3;
- privatefinalstaticintTASK_END=4;
- privatefinalstaticintTASK_BEGIN_OVER=11;
- privatefinalstaticintTASK_1_OVER=12;
- privatefinalstaticintTASK_2_OVER=13;
- privatefinalstaticintTASK_END_OVER=14;
- privateHandlerworkHandler=null;
- /**Calledwhentheactivityisfirstcreated.*/
- @Override
- publicvoidonCreate(BundlesavedInstanceState){
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- Log.i(TAG,"[M_TID:"+Thread.currentThread().getId()+"]"+
- "Thisisinmainthread.");
- LooperThreadtestThread=newLooperThread();
- testThread.start();
- //注意,这里需要等待一下,防止出现空指针异常
- while(null==workHandler){
- }
- testThread.sendMessageTodoYourWork();
- }
- HandlermainHandler=newHandler(){
- //在每个case之后,不能做耗时的操作
- @Override
- publicvoidhandleMessage(Messagemsg){
- switch(msg.what){
- caseTASK_BEGIN_OVER:
- Log.i(TAG,"[MH_TID:"+
- Thread.currentThread().getId()+"]TASK_BEGIN_OVER");
- break;
- caseTASK_1_OVER:
- Log.i(TAG,"[MH_TID:"+
- Thread.currentThread().getId()+"]TASK_1_OVER");
- break;
- caseTASK_2_OVER:
- Log.i(TAG,"[MH_TID:"+
- Thread.currentThread().getId()+"]TASK_2_OVER");
- break;
- caseTASK_END_OVER:
- Log.i(TAG,"[MH_TID:"+
- Thread.currentThread().getId()+"]TASK_END_OVER");
- finish();
- break;
- }
- super.handleMessage(msg);
- }
- };
- classLooperThreadextendsThread{
- @Override
- publicvoidrun(){
- Looper.prepare();
- workHandler=newHandler(){
- //现在在每个case之后,你可以做任何耗时的操作了
- @Override
- publicvoidhandleMessage(Messagemsg){
- switch(msg.what){
- caseTASK_BEGIN:
- Log.i(TAG,"[ZH_TID:"+
- Thread.currentThread().getId()+"]GetTASK_BEGIN");
- //做完之后报告信息给主线程
- mainHandler.sendEmptyMessage(TASK_BEGIN_OVER);
- break;
- caseTASK_1:
- Log.i(TAG,"[ZH_TID:"+
- Thread.currentThread().getId()+"]GetTASK_1");
- //做完之后报告信息给主线程
- mainHandler.sendEmptyMessage(TASK_1_OVER);
- break;
- caseTASK_2:
- Log.i(TAG,"[ZH_TID:"+
- Thread.currentThread().getId()+"]GetTASK_2");
- //做完之后报告信息给主线程
- mainHandler.sendEmptyMessage(TASK_2_OVER);
- break;
- caseTASK_END:
- Log.i(TAG,"[ZH_TID:"+
- Thread.currentThread().getId()+"]GetTASK_END");
- Looper.myLooper().quit();
- //做完之后报告信息给主线程
- mainHandler.sendEmptyMessage(TASK_END_OVER);
- Looper.myLooper().quit();
- break;
- }
- super.handleMessage(msg);
- }
- };
- Looper.loop();
- }
- publicvoidsendMessageTodoYourWork(){
- Log.i(TAG,"[ZS_ID:"+Thread.currentThread().getId()+"]"+
- "SendTASK_STARTtohandler.");
- //启动任务(消息只有标识,立即投递)
- workHandler.sendEmptyMessage(TASK_BEGIN);
- Log.i(TAG,"[ZS_ID:"+Thread.currentThread().getId()+"]"+
- "SendTASK_1tohandler.");
- //开始任务1(在workHandler的消息队列中获取一个Message对象,避免重复构造)
- Messagemsg1=workHandler.obtainMessage(TASK_1);
- msg1.obj="Thisistask1";
- workHandler.sendMessage(msg1);
- Log.i(TAG,"[ZS_ID:"+Thread.currentThread().getId()+"]"+
- "SendTASK_2tohandler.");
- //开启任务2(和上面类似)
- Messagemsg2=Message.obtain();
- msg2.arg1=10;
- msg2.arg2=20;
- msg2.what=TASK_2;
- workHandler.sendMessage(msg2);
- Log.i(TAG,"[ZS_ID:"+Thread.currentThread().getId()+"]"+
- "SendTASK_ENDtohandler.");
- //结束任务(空消息体,延时2s投递)
- workHandler.sendEmptyMessageDelayed(TASK_END,2000);
- }
- }
- }
运行结果:
小结:Handler在Android中是很常用的,或是用来更新UI,或是派发任务给子线程去执行,也可以用来产生超时效果,比如用sendMessageDelayed(TASK_TIMEOUT, OUT_TIME)方法。
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