android的Handler
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
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(Looper looper)、Handler(Looper looper, Handler.Callback callback)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
<?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>
<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
@Override
publicvoid 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);
}
publicvoid 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.Callback callback)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
@Override
publicvoid onClick(View v) {
switch (v.getId()) {
case R.id.btnStartTime:
startTimer();
break;
case R.id.btnStopTime:
timer.cancel();
break;
}
}
privatesynchronizedvoid 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。
privatevoid 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
publicvoid TaskRun() {
updateTimerValues();
}
@Override
publicvoid onClick(View v) {
switch (v.getId()) {
case R.id.btnStartTime:
startTimer();
break;
case R.id.btnStopTime:
timer.cancel();
break;
}
}
privatesynchronizedvoid 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。
privatevoid 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
publicvoid 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
publicinterface ITaskCallBack {
void TaskRun();
}
publicclass Task extends TimerTask {
private ITaskCallBack iTask;
public Task(ITaskCallBack iTaskCallBack)
{
super();
iTask=iTaskCallBack;
}
publicvoid setCallBack(ITaskCallBack iTaskCallBack)
{
iTask=iTaskCallBack;
}
@Override
publicvoid run() {
// TODO Auto-generated method stub
iTask.TaskRun();
}
}
void TaskRun();
}
publicclass Task extends TimerTask {
private ITaskCallBack iTask;
public Task(ITaskCallBack iTaskCallBack)
{
super();
iTask=iTaskCallBack;
}
publicvoid setCallBack(ITaskCallBack iTaskCallBack)
{
iTask=iTaskCallBack;
}
@Override
publicvoid run() {
// TODO Auto-generated method stub
iTask.TaskRun();
}
}
这是Java的回调函数的一般写法。
实现CallBack
/**
* 实现消息处理
*/
@Override
publicboolean handleMessage(Message msg) {
switch(msg.what)
{
case0:
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;
}
returnfalse;
}
/**
* 实现消息处理
*/
@Override
publicboolean handleMessage(Message msg) {
switch(msg.what)
{
case0:
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;
}
returnfalse;
}
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
publicclass ThreadHandlerrActivity extends Activity implements Callback,
OnClickListener {
private TextView txt;
private Button btnStart, btnStop;
private Handler myHandler;
private TimerThread timerThread;
privateint Total=30;
/** Called when the activity is first created. */
@Override
publicvoid 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
publicboolean handleMessage(Message msg) {
switch(msg.what)
{
case0:
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;
}
returnfalse;
}
@Override
publicvoid 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;
}
}
}
publicclass ThreadHandlerrActivity extends Activity implements Callback,
OnClickListener {
private TextView txt;
private Button btnStart, btnStop;
private Handler myHandler;
private TimerThread timerThread;
privateint Total=30;
/** Called when the activity is first created. */
@Override
publicvoid 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
publicboolean handleMessage(Message msg) {
switch(msg.what)
{
case0:
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;
}
returnfalse;
}
@Override
publicvoid 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
**
* 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
*
*/
publicclass TimerThread extends Thread {
publicint 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
publicvoid 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();
}
}
* 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
*
*/
publicclass TimerThread extends Thread {
publicint 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
publicvoid 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
publicclass PostHandler extends Activity implements OnClickListener, Runnable {
private TextView txt;
private Button btnStart, btnStop;
private Handler myHandler;
private Timer timer;
privateint total =60;
@Override
protectedvoid 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
publicvoid handleMessage(Message msg) {
switch(msg.what)
{
case0:
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
publicvoid onClick(View v) {
switch (v.getId()) {
case R.id.btnStartTime:
//myHandler.post(this);
myHandler.postDelayed(this, 1000);
break;
case R.id.btnStopTime:
break;
}
}
@Override
publicvoid 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()));
}
}
}
publicclass PostHandler extends Activity implements OnClickListener, Runnable {
private TextView txt;
private Button btnStart, btnStop;
private Handler myHandler;
private Timer timer;
privateint total =60;
@Override
protectedvoid 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
publicvoid handleMessage(Message msg) {
switch(msg.what)
{
case0:
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
publicvoid onClick(View v) {
switch (v.getId()) {
case R.id.btnStartTime:
//myHandler.post(this);
myHandler.postDelayed(this, 1000);
break;
case R.id.btnStopTime:
break;
}
}
@Override
publicvoid 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
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;
publicclass PostHandler extends Activity implements OnClickListener, Runnable {
private TextView txt;
private Button btnStart, btnStop;
private Handler myHandler;
private Timer timer;
privateint total =60;
private TimerThread timerThread;
@Override
protectedvoid 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
publicvoid handleMessage(Message msg) {
switch(msg.what)
{
case0:
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
publicvoid 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
publicvoid 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()));
}
}
}
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;
publicclass PostHandler extends Activity implements OnClickListener, Runnable {
private TextView txt;
private Button btnStart, btnStop;
private Handler myHandler;
private Timer timer;
privateint total =60;
private TimerThread timerThread;
@Override
protectedvoid 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
publicvoid handleMessage(Message msg) {
switch(msg.what)
{
case0:
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
publicvoid 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
publicvoid 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)”。