android的Handler
16lz
2021-12-04
前言
学习android一段时间了,为了进一步了解android的应用是如何设计开发的,决定详细研究几个开源的android应用。从一些开源应用中吸收点东西,一边进行量的积累,一边探索android的学习研究方向。这里我首先选择了jwood的 Standup Timer项目。本文将把研究的内容笔记整理,建立一个索引列表。关键词
Android.os.Handler涉及较多的知识点,我把一些关键词列举在下面,将主要介绍Handler:- android.os.Handler 、 android.os.Handler.Callback
- Looper、
- Threadle、Runnable
- Message、Message queue
android.os.Handler
Handler在android里负责发送和处理消息。它的主要用途有: 1)按计划发送消息或执行某个Runnanble(使用POST方法); 2)从其他线程中发送来的消息放入消息队列中,避免线程冲突(常见于更新UI线程) 默认情况下,Handler接受的是当前线程下的消息循环实例(使用 Handler( Looperlooper)、 Handler( Looperlooper, Handler.Callbackcallback)可以指定线程),同时一个消息队列可以被当前线程中的多个对象进行分发、处理(在UI线程中,系统已经有一个Activity来处理了,你可以再起若干个Handler来处理)。在实例化Handler的时候,Looper可以是任意线程的,只要有Handler的指针,任何线程也都可以sendMessage。Handler对于Message的处理不是并发的。一个Looper 只有处理完一条Message才会读取下一条,所以消息的处理是阻塞形式的(handleMessage()方法里不应该有耗时操作,可以将耗时操作放在其他线程执行,操作完后发送Message(通过sendMessges方法),然后由handleMessage()更新UI)。倒计时程序
利用Timer 编写一个倒计时程序,程序使用Timer和TimerTask来完成倒计时,同时使用sendMessages方法发送消息,然后在HanleMessage里更新UI。 Activity布局: Layout<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--> <? xml version="1.0" encoding="utf-8" ?> < LinearLayout xmlns:android ="http://schemas.android.com/apk/res/android" android:orientation ="vertical" android:layout_width ="fill_parent" android:layout_height ="fill_parent" > < TextView android:layout_width ="fill_parent" android:layout_height ="wrap_content" android:layout_gravity ="center" android:id ="@+id/txt" /> < Button android:id ="@+id/btnStartTime" android:text ="开始计时" android:layout_width ="80dip" android:layout_height ="wrap_content" ></ Button > < Button android:id ="@+id/btnStopTime" android:text ="停止计时" android:layout_width ="80dip" android:layout_height ="wrap_content" /> < SeekBar android:id ="@+id/SeekBar01" android:layout_width ="match_parent" android:layout_height ="wrap_content" ></ SeekBar > </ LinearLayout >这里使用TextView 来显示倒计时的时间变化,两个按钮用于控制时间的开始和停止。SeekBar主要是用于查看线程是否被阻塞(阻塞时无法拖动)。 onCreate
<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--> @Override public void onCreate(Bundle savedInstanceState) { super .onCreate(savedInstanceState); setContentView(R.layout.main); txt = (TextView) findViewById(R.id.txt); btnStart = (Button) findViewById(R.id.btnStartTime); btnStop = (Button) findViewById(R.id.btnStopTime); Log.d( " ThreadId " , " onCread: " + String.valueOf(Thread.currentThread().getId())); myHandler = new Handler( this ); btnStart.setOnClickListener( this ); btnStop.setOnClickListener( this ); }在onCreate方法中初始化元素个元素,myHandler = new Handler(this); 调用的是 Handler( Handler.Callbackcallback)构造函数,在回调方法callback中对发送来的消息进行处理(这样我们就不必使用内部类的写法来 重写HandleMessage()方法了),因此Activity必须实现 android.os.Handler.Callback接口。我们还在将onCreate 方法的ThreadId 记录在了Log中用以和消息发送、处理时所作的线程进行比较。 发送消息
<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--> @Override public void onClick(View v) { switch (v.getId()) { case R.id.btnStartTime: startTimer(); break ; case R.id.btnStopTime: timer.cancel(); break ; } } private synchronized void startTimer() { timer = new Timer(); // TimerTask updateTimerValuesTask = new TimerTask() { // @Override // public void run() { // updateTimerValues(); // } // // }; // 自定义的CallBack模式。Task继承自TimerTask Task updateTimerValuesTask = new Task( this ); timer.schedule(updateTimerValuesTask, 1000 , 1000 ); } // 执行耗时的倒计时任务。 private void updateTimerValues() { total -- ; Log.d( " ThreadId " , " send: " + String.valueOf(Thread.currentThread().getId())); Message msg = new Message(); Bundle date = new Bundle(); // 存放数据 date.putInt( " time " , total); msg.setData(date); msg.what = 0 ; myHandler.sendMessage(msg); // 另一种写法 // Message msg=myHandler.obtainMessage(); // Bundle date = new Bundle(); // 存放数据 // date.putInt("time", total); // msg.setData(date); // msg.what=0; // msg.sendToTarget(); } @Override public void TaskRun() { updateTimerValues(); }实现Button按钮的事件处理以此进入倒计时操作。这里使用的Timer 来执行定时操作(其实我们完全可以另起一个线程)。Task类继承了TimerTask类,里面增加了一个任务处理接口来实现回调模式,应此Activity需要实现该回调的接口ITaskCallBack(这样做是因为我比较不喜欢内部类的编写方法)。 ICallBack接口和Task类
<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--> public interface ITaskCallBack { void TaskRun(); } public class Task extends TimerTask { private ITaskCallBack iTask; public Task(ITaskCallBack iTaskCallBack) { super (); iTask = iTaskCallBack; } public void setCallBack(ITaskCallBack iTaskCallBack) { iTask = iTaskCallBack; } @Override public void run() { // TODO Auto-generated method stub iTask.TaskRun(); } }这是Java的回调函数的一般写法。 实现CallBack
<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--> /** * 实现消息处理 */ @Override public boolean handleMessage(Message msg) { switch (msg.what) { case 0 : Bundle date = msg.getData(); txt.setText(String.valueOf(date.getInt( " time " ))); Log.d( " ThreadId " , " HandlerMessage: " + String.valueOf(Thread.currentThread().getId())); Log.d( " ThreadId " , " msgDate: " + String.valueOf(date.getInt( " time " ))); break ; } return false ; }可以看到实现 android.os.Handler.Callback接口,其实就是对handleMessage()方法进行重写(和内部类的一个区别是,内部类的返回值是Void)。
运行结果
可以看到在onCreate 方法中线程的ID是1(UI线程) 这与 HandlerMessage 进行消息处理时是所作的线程ID是一样的,而消息发送的线程ID则为8非UI线程。使用Threadle进行实现
Activity类<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--> public class ThreadHandlerrActivity extends Activity implements Callback, OnClickListener { private TextView txt; private Button btnStart, btnStop; private Handler myHandler; private TimerThread timerThread; private int Total = 30 ; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super .onCreate(savedInstanceState); setContentView(R.layout.main); txt = (TextView) findViewById(R.id.txt); btnStart = (Button) findViewById(R.id.btnStartTime); btnStop = (Button) findViewById(R.id.btnStopTime); Log.d( " ThreadId " , " onCread: " + String.valueOf(Thread.currentThread().getId())); myHandler = new Handler( this ); btnStart.setOnClickListener( this ); btnStop.setOnClickListener( this ); } /** * 实现消息处理 */ @Override public boolean handleMessage(Message msg) { switch (msg.what) { case 0 : Bundle date = msg.getData(); txt.setText(String.valueOf(date.getInt( " time " ))); Log.d( " ThreadId " , " HandlerMessage: " + String.valueOf(Thread.currentThread().getId())); Log.d( " ThreadId " , " msgDate: " + String.valueOf(date.getInt( " time " ))); break ; } return false ; } @Override public void onClick(View v) { switch (v.getId()) { case R.id.btnStartTime: // 自定义的线程 timerThread = new TimerThread(myHandler, 60 ); timerThread.start(); break ; case R.id.btnStopTime: timerThread.stop(); // timerThread.destroy(); break ; } } }自定义的线程类
<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--> ** * 自定义的线程类,通过传入的Handler,和Total 定期执行耗时操作 * @author linzijun * */ public class TimerThread extends Thread { public int Total = 60 ; public Handler handler; /** * 初始化构造函数 * @param mhandler handler 用于发送消息 * @param total 总周期 */ public TimerThread(Handler mhandler, int total) { super (); handler = mhandler; Total = total; } @Override public void run() { while ( true ) { Total -- ; if (Total < 0 ) break ; try { Thread.sleep( 1000 ); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } Message msg = new Message(); Bundle date = new Bundle(); // 存放数据 date.putInt( " time " , Total); msg.setData(date); msg.what = 0 ; Log.d( " ThreadId " , " Thread: " + String.valueOf(Thread.currentThread().getId())); handler.sendMessage(msg); } super .run(); } }这里继承了Thread类,也可以直接实现 Runnable接口。
关于POST
Post的各种方法是把一个Runnable发送给消息队列,它将在到达时进行处理。 POST<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--> public class PostHandler extends Activity implements OnClickListener, Runnable { private TextView txt; private Button btnStart, btnStop; private Handler myHandler; private Timer timer; private int total = 60 ; @Override protected void onCreate(Bundle savedInstanceState) { // TODO Auto-generated method stub super .onCreate(savedInstanceState); setContentView(R.layout.main); txt = (TextView) findViewById(R.id.txt); btnStart = (Button) findViewById(R.id.btnStartTime); btnStop = (Button) findViewById(R.id.btnStopTime); Log.d( " ThreadId " , " onCread: " + String.valueOf(Thread.currentThread().getId())); myHandler = new Handler() { @Override public void handleMessage(Message msg) { switch (msg.what) { case 0 : Bundle date = msg.getData(); txt.setText(String.valueOf(date.getInt( " time " ))); Log.d( " ThreadId " , " HandlerMessage: " + String.valueOf(Thread.currentThread().getId())); Log.d( " ThreadId " , " msgDate: " + String.valueOf(date.getInt( " time " ))); break ; } } }; btnStart.setOnClickListener( this ); btnStop.setOnClickListener( this ); } @Override public void onClick(View v) { switch (v.getId()) { case R.id.btnStartTime: // myHandler.post(this); myHandler.postDelayed( this , 1000 ); break ; case R.id.btnStopTime: break ; } } @Override public void run() { while ( true ) { total -- ; if (total < 0 ) break ; try { Thread.sleep( 1000 ); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } Message msg = new Message(); Bundle date = new Bundle(); // 存放数据 date.putInt( " time " , total); msg.setData(date); msg.what = 0 ; Log.d( " ThreadId " , " POST: " + String.valueOf(Thread.currentThread().getId())); myHandler.sendMessage(msg); Log.d( " ThreadId " , " Thread: " + String.valueOf(Thread.currentThread().getId())); } } }使用POST的方式 是将Runnable 一起发送给处理的线程(这里为UI),如果Runnable的操作比较耗时的话那线程将进入阻塞状态。可以看到先运行 Runnable的Run方法 然后在进入 HandleMessage() 。我还尝试了另一种写法,将TimerThreadPOST过去,运行结果是一样的。 代码
<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--> package zijunlin.me; import java.util.Timer; import android.app.Activity; import android.os.Bundle; import android.os.Handler; import android.os.Message; import android.util.Log; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.TextView; public class PostHandler extends Activity implements OnClickListener, Runnable { private TextView txt; private Button btnStart, btnStop; private Handler myHandler; private Timer timer; private int total = 60 ; private TimerThread timerThread; @Override protected void onCreate(Bundle savedInstanceState) { // TODO Auto-generated method stub super .onCreate(savedInstanceState); setContentView(R.layout.main); txt = (TextView) findViewById(R.id.txt); btnStart = (Button) findViewById(R.id.btnStartTime); btnStop = (Button) findViewById(R.id.btnStopTime); Log.d( " ThreadId " , " onCread: " + String.valueOf(Thread.currentThread().getId())); myHandler = new Handler() { @Override public void handleMessage(Message msg) { switch (msg.what) { case 0 : Bundle date = msg.getData(); txt.setText(String.valueOf(date.getInt( " time " ))); Log.d( " ThreadId " , " HandlerMessage: " + String.valueOf(Thread.currentThread().getId())); Log.d( " ThreadId " , " msgDate: " + String.valueOf(date.getInt( " time " ))); break ; } } }; btnStart.setOnClickListener( this ); btnStop.setOnClickListener( this ); } @Override public void onClick(View v) { switch (v.getId()) { case R.id.btnStartTime: // myHandler.post(this); // myHandler.postDelayed(this, 1000); timerThread = new TimerThread(myHandler, 60 ); myHandler.post(timerThread); break ; case R.id.btnStopTime: break ; } } @Override public void run() { while ( true ) { total -- ; if (total < 0 ) break ; try { Thread.sleep( 1000 ); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } Message msg = new Message(); Bundle date = new Bundle(); // 存放数据 date.putInt( " time " , total); msg.setData(date); msg.what = 0 ; Log.d( " ThreadId " , " POST: " + String.valueOf(Thread.currentThread().getId())); myHandler.sendMessage(msg); Log.d( " ThreadId " , " Thread: " + String.valueOf(Thread.currentThread().getId())); } } }可以说POST的各种方法主要是用于 “按计划发送消息或执行某个Runnanble(使用POST方法)”。
参考文献
android学习笔记之消息机制,异步和多线程 android handler概念解释 SDK系列索引
Android 开源项目-StandupTimer学习笔记索引更多相关文章
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