先看演示：
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。
1为什么使用Handler
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）
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；
若在主线程中实例化一个Handler对象，例如：
Handler mHandler = 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！
2 例子
下面就Handler的使用举一些例子，加深理解。
2.1、post版本的Handler
public class MainActivity extends Activity
implements OnClickListener {
private final static String TAG = "HandlerTest";
private final static int DELAY_TIME = 1000;
private Button btnStart;
private Button btnStop;
Context mContext = null;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mContext = this;
Log.i(TAG, "Main thread id = " +
Thread.currentThread().getId());
btnStart = (Button) findViewById(R.id.btn_start);
btnStart.setOnClickListener(this);
btnStop = (Button) findViewById(R.id.btn_stop);
btnStop.setOnClickListener(this);
}
@Override
public void onClick(View view) {
switch (view.getId()) {
case R.id.btn_start:
mHandler.postDelayed(workRunnable, DELAY_TIME);
break;
case R.id.btn_stop:
mHandler.removeCallbacks(workRunnable);
break;
}
}
Runnable workRunnable = new Runnable() {
int counter = 0;
public void run() {
if (counter++ < 1) {
Log.i(TAG, "workRunnable thread id = " +
Thread.currentThread().getId());
mHandler.postDelayed(workRunnable, DELAY_TIME);
}
}
};
Handler mHandler = new Handler();
}
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。
2.2 HandlerThread
public class MyThread2 extends Activity {
private Handler handler = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
HandlerThread handlerThread = new HandlerThread("myHandlerThread");
handlerThread.start();
handler = new Handler(handlerThread.getLooper());
handler.post(new MyRunnable());
System.out.println("Oncreate---The Thread id is :"
+ Thread.currentThread().getId());
setContentView(R.layout.main);
}
private class MyRunnable implements Runnable {
public void run() {
System.out.println("Runnable---The Thread is running");
System.out.println("Runnable---The Thread id is :"
+ Thread.currentThread().getId());
try {
Thread.sleep(6000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
在这个demo中,用到了HandlerThread,在HandlerThread对象中可以通过getLooper方法获取一个Looper对象控制句柄，我们可以将其这个Looper对象映射到一个Handler中去来实现一个线程同步机制。于是就有以下结果;
1：控制台的输出： Oncreate---The Thread id is :1
Runnable---The Threadis running
Runnable---The Threadid is :10
2：程序启动后,我们立刻看到main.xml中的内容。
这样就达到了多线程的结果
2.3 sendMessage版本的Handler
这里介绍几种模型:
2.3.1 默认的Handler
（消息处理队列挂在主线程上）
public class MainActivity extends Activity
implements OnClickListener {
private final static String TAG = "HandlerTest";
private final static int TASK_BEGIN = 1;
private final static int TASK_1 = 2;
private final static int TASK_2 = 3;
private final static int TASK_END = 4;
private Button btnStart = null;
private Button btnStop = null;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
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() + "]");
}
Handler mHandler = new Handler() {
// 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
public void handleMessage(Message msg) {
switch (msg.what) {
case TASK_BEGIN:
Log.i(TAG, "[H_TID:" +
Thread.currentThread().getId() + "] Get TASK_BEGIN");
break;
case TASK_1:
Log.i(TAG, "[H_TID:" +
Thread.currentThread().getId() + "] Get TASK_1");
break;
case TASK_2:
Log.i(TAG, "[H_TID:" +
Thread.currentThread().getId() + "] Get TASK_2");
break;
case TASK_END:
Log.i(TAG, "[H_TID:" +
Thread.currentThread().getId() + "] Get TASK_END");
finish();
break;
}
super.handleMessage(msg);
}
};
public void onClick(View view) {
switch (view.getId()) {
case R.id.btn_start:
// 启动任务（消息只有标识，立即投递）
mHandler.sendEmptyMessage(TASK_BEGIN);
Log.i(TAG, "Send TASK_BEGIN to handler.");
// 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）
Message msg1 = mHandler.obtainMessage(TASK_1);
msg1.obj = "This is task1";
mHandler.sendMessage(msg1);
Log.i(TAG, "Send TASK_1 to handler.");
// 开启任务2（和上面类似）
Message msg2 = Message.obtain();
msg2.arg1 = 10;
msg2.arg2 = 20;
msg2.what = TASK_2;
mHandler.sendMessage(msg2);
Log.i(TAG, "Send TASK_2 to handler.");
break;
case R.id.btn_stop:
// 结束任务（空消息体，延时2s投递）
mHandler.sendEmptyMessageDelayed(TASK_END, 2000);
Log.i(TAG, "Send TASK_END to handler.");
break;
}
}
} 2.3.2消息队列仍绑定在主线程上
在子线程中发送消息。
public class MainActivity extends Activity {
private final static String TAG = "HandlerTest";
private final static int TASK_BEGIN = 1;
private final static int TASK_1 = 2;
private final static int TASK_2 = 3;
private final static int TASK_END = 4;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Log.i(TAG, "[M_TID:" + Thread.currentThread().getId() + "]" +
"This is in main thread.");
workThread.start();
}
Handler mHandler = new Handler() {
// 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
public void handleMessage(Message msg) {
switch (msg.what) {
case TASK_BEGIN:
Log.i(TAG, "[H_TID:" +
Thread.currentThread().getId() + "] Get TASK_BEGIN");
break;
case TASK_1:
Log.i(TAG, "[H_TID:" +
Thread.currentThread().getId() + "] Get TASK_1");
break;
case TASK_2:
Log.i(TAG, "[H_TID:" +
Thread.currentThread().getId() + "] Get TASK_2");
break;
case TASK_END:
Log.i(TAG, "[H_TID:" +
Thread.currentThread().getId() + "] Get TASK_END");
finish();
break;
}
super.handleMessage(msg);
}
};
Thread workThread = new Thread() {
// 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
public void run() {
// 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() + "]" +
"Send TASK_START to handler.");
// 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）
Message msg1 = mHandler.obtainMessage(TASK_1);
msg1.obj = "This is task1";
mHandler.sendMessage(msg1);
Log.i(TAG, "[S_TID:" + Thread.currentThread().getId() + "]" +
"Send TASK_1 to handler.");
// 开启任务2（和上面类似）
Message msg2 = Message.obtain();
msg2.arg1 = 10;
msg2.arg2 = 20;
msg2.what = TASK_2;
mHandler.sendMessage(msg2);
Log.i(TAG, "[S_TID:" + Thread.currentThread().getId() + "]" +
"Send TASK_2 to handler.");
// 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() + "]" +
"Send TASK_END to handler.");
}
};
} 2.3.3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。
public class MainActivity extends Activity {
private final static String TAG = "HandlerTest";
private final static int TASK_BEGIN = 1;
private final static int TASK_1 = 2;
private final static int TASK_2 = 3;
private final static int TASK_END = 4;
private MyHandler mHandler = null;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Log.i(TAG, "[M_TID:" + Thread.currentThread().getId() + "]" +
"This is in main thread.");
HandlerThread myLooperThread = new HandlerThread("my looper thread");
myLooperThread.start();
Looper looper = myLooperThread.getLooper();
mHandler = new MyHandler(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() + "]" +
"Send TASK_START to handler.");
// 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）
Message msg1 = mHandler.obtainMessage(TASK_1);
msg1.obj = "This is task1";
mHandler.sendMessage(msg1);
Log.i(TAG, "[S_ID:" + Thread.currentThread().getId() + "]" +
"Send TASK_1 to handler.");
// 开启任务2（和上面类似）
Message msg2 = Message.obtain();
msg2.arg1 = 10;
msg2.arg2 = 20;
msg2.what = TASK_2;
mHandler.sendMessage(msg2);
Log.i(TAG, "[S_ID:" + Thread.currentThread().getId() + "]" +
"Send TASK_2 to handler.");
// 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() + "]" +
"Send TASK_END to handler.");
}
class MyHandler extends Handler {
public MyHandler(Looper looper) {
super(looper);
}
// 现在在每个case之后，你可以做任何耗时的操作了
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case TASK_BEGIN:
Log.i(TAG, "[H_TID:" +
Thread.currentThread().getId() + "] Get TASK_BEGIN");
break;
case TASK_1:
Log.i(TAG, "[H_TID:" +
Thread.currentThread().getId() + "] Get TASK_1");
break;
case TASK_2:
Log.i(TAG, "[H_TID:" +
Thread.currentThread().getId() + "] Get TASK_2");
break;
case TASK_END:
Log.i(TAG, "[H_TID:" +
Thread.currentThread().getId() + "] Get TASK_END");
finish();
break;
}
super.handleMessage(msg);
}
}
}
3 Demo源码
package mm.shandong.com.testhandler;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;
import android.widget.Toast;
import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;
public class TestHandlerActivity extends AppCompatActivity {
TextView textView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_test_handler);
textView= (TextView) findViewById(R.id.textView);
}
public void createSimpleHandler(View view){
final Handler handler=new Handler(){
@Override
public void handleMessage(Message msg) {
switch (msg.what){
case 1:///一般用16进制表示如0x0001
textView.setText(String.valueOf(msg.arg1));
break;
}
}
};
new Thread(){
@Override
public void run() {
int i=0;
while (i<50){
try {
Thread.sleep(100);
Message msg=new Message();
msg.what=1;
msg.arg1=i;
handler.sendMessage(msg);
i++;
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}.start();
}
public void createSimpleHandler2(View view){
final Handler handler=new Handler(){
@Override
public void handleMessage(Message msg) {
switch (msg.what){
case 0x0002:///一般用16进制表示如0x0001
Bundle bundle=msg.getData();
Map map= (Map) bundle.get("map");
String name= (String) map.get("name");
textView.setText(name);
break;
}
}
};
new Thread(){
@Override
public void run() {
int i=0;
while (i<50){
try {
Thread.sleep(100);
Message msg=new Message();
msg.what=0x0002;
Bundle bundle=new Bundle();
Map map=new HashMap<>();
map.put("name","张三"+i);
bundle.putSerializable("map", (Serializable) map);
msg.setData(bundle);
handler.sendMessage(msg);
i++;
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}.start();
}
public void createSimpleHandler3(View view){
final Handler handler=new Handler(){
@Override
public void handleMessage(Message msg) {
switch (msg.what){
case 1:///一般用16进制表示如0x0001
Toast.makeText(TestHandlerActivity.this,"这是一条空消息",Toast.LENGTH_SHORT).show();
break;
}
}
};
handler.sendEmptyMessage(1);
}
public void createSimpleHandler4(View view){
final Handler handler=new Handler(){
@Override
public void handleMessage(Message msg) {
switch (msg.what){
case 1:///一般用16进制表示如0x0001
Toast.makeText(TestHandlerActivity.this,"这是延迟发送的一条空消息",Toast.LENGTH_SHORT).show();
break;
}
}
};
handler.sendEmptyMessageDelayed(1,2000);
}
public void createSimpleHandler5(View view){
final Handler handler=new Handler(){
@Override
public void handleMessage(Message msg) {
switch (msg.what){
case 1:///一般用16进制表示如0x0001
Toast.makeText(TestHandlerActivity.this,"这是通过obtainMessage从消息池中得到一条消息并发送，" +
""+"参数是:"+msg.arg1,Toast.LENGTH_LONG).show();
break;
}
}
};
Message msg=handler.obtainMessage();
msg.what=1;
msg.arg1=3;
handler.sendMessage(msg);
}
public void createSimpleHandler6(View view){
MThreadNoLooper mThreadNoLooper=new MThreadNoLooper();
mThreadNoLooper.start();
if(mThreadNoLooper.handler!=null){
mThreadNoLooper.handler.sendEmptyMessage(1);
}
}
public void createSimpleHandler7(View view){
MThread mThread=new MThread();
mThread.start();
try {
Thread.sleep(100);
if(mThread.handler!=null){
mThread.handler.sendEmptyMessage(1);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public class MThreadNoLooper extends Thread{
public Handler handler;
@Override
public void run() {
handler=new Handler(){
@Override
public void handleMessage(Message msg) {
switch (msg.what){
case 1:///一般用16进制表示如0x0001
Toast.makeText(TestHandlerActivity.this,"这是子线程中的handler监听到的消息",Toast.LENGTH_LONG).show();
break;
}
}
};
}
}
public class MThread extends Thread{
public Handler handler;
@Override
public void run() {
Looper.prepare();
handler=new Handler(){
@Override
public void handleMessage(Message msg) {
switch (msg.what){
case 1:///一般用16进制表示如0x0001
Toast.makeText(TestHandlerActivity.this,"这是子线程中的handler监听到的消息",Toast.LENGTH_LONG).show();
break;
}
}
};
Looper.loop();
}
}
}
本人微博：honey_11
Demo下载
最后，以上例子都来源与android学习手册，请去360手机助手下载：例子源码，源码例子文档一网打尽。
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