Handler Looper MessageQuene

Handler有两个重要方法sendMessage(Message msg)和handleMessage(Message msg)

MessageQuene是Message的队列

Looper对MessageQuene操作，插入Message和取出Message

Handler实现了回调方法，获得Looper取得的Message

每个线程中的Handler必定有个并且只有一个与之对应的Looper，但是主线程中已经有Looper了

所以Handler在主线程中可以直接handleMessage

但是如果Handler不在主线程中需要调用Looper

Looper不能直接构造，要调用Looper.prepare()方法，在handleMessage(msg)之后调用Looper.loop()方法

下面代码是第一种情况

Handler在主线程中handleMessage

public class MainActivity extends Activity{Button bt;Handler handler1;Thread2 thread;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);bt=(Button) findViewById(R.id.main_bt);/*thread=new Thread2();thread.start();*/handler1=new Handler(){@Overridepublic void handleMessage(Message msg) {// TODO Auto-generated method stubsuper.handleMessage(msg);Log.e("sjj", "handleMessage"+msg.what);switch(msg.what){case 123:Toast.makeText(MainActivity.this, "get1",Toast.LENGTH_LONG).show();}}};bt.setOnClickListener(new OnClickListener(){@Overridepublic void onClick(View arg0) {// TODO Auto-generated method stubnew MyThread().start();//thread.handler2.sendEmptyMessage(321);}});}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {// Inflate the menu; this adds items to the action bar if it is present.getMenuInflater().inflate(R.menu.activity_main, menu);return true;}class MyThread extends Thread{int i=0;public MyThread() {super();// TODO Auto-generated constructor stub}public MyThread(Runnable runnable) {super(runnable);// TODO Auto-generated constructor stub}@Overridepublic void run() {// TODO Auto-generated method stubtry {while(i<10){i++;this.sleep(1000);Log.e("sjj", "i="+i);}handler1.sendEmptyMessage(123);Log.e("sjj", "sendMessage");} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}class Thread2 extends Thread{Handler handler2;@Overridepublic void run() {// TODO Auto-generated method stubsuper.run();//Looper.prepare();handler2=new Handler(){@Overridepublic void handleMessage(Message msg) {// TODO Auto-generated method stubsuper.handleMessage(msg);if(msg.what==321){Toast.makeText(MainActivity.this, "get2", Toast.LENGTH_LONG).show();}}};//Looper.loop();}}}

01-15 20:47:28.781: E/sjj(3925): i=1
01-15 20:47:29.782: E/sjj(3925): i=2
01-15 20:47:30.782: E/sjj(3925): i=3
01-15 20:47:31.783: E/sjj(3925): i=4
01-15 20:47:32.783: E/sjj(3925): i=5
01-15 20:47:33.784: E/sjj(3925): i=6
01-15 20:47:34.785: E/sjj(3925): i=7
01-15 20:47:35.786: E/sjj(3925): i=8
01-15 20:47:36.786: E/sjj(3925): i=9
01-15 20:47:37.788: E/sjj(3925): i=10
01-15 20:47:37.788: E/sjj(3925): sendMessage
01-15 20:47:37.798: E/sjj(3925): handleMessage123

下面代码是第二种情况，Handler在其他线程中handleMessage

直接使用报错

public class MainActivity extends Activity{Button bt;Handler handler1;Thread2 thread;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);bt=(Button) findViewById(R.id.main_bt);thread=new Thread2();thread.start();handler1=new Handler(){@Overridepublic void handleMessage(Message msg) {// TODO Auto-generated method stubsuper.handleMessage(msg);Log.e("sjj", "handleMessage"+msg.what);switch(msg.what){case 123:Toast.makeText(MainActivity.this, "get1",Toast.LENGTH_LONG).show();}}};bt.setOnClickListener(new OnClickListener(){@Overridepublic void onClick(View arg0) {// TODO Auto-generated method stub//new MyThread().start();thread.handler2.sendEmptyMessage(321);}});}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {// Inflate the menu; this adds items to the action bar if it is present.getMenuInflater().inflate(R.menu.activity_main, menu);return true;}class MyThread extends Thread{int i=0;public MyThread() {super();// TODO Auto-generated constructor stub}public MyThread(Runnable runnable) {super(runnable);// TODO Auto-generated constructor stub}@Overridepublic void run() {// TODO Auto-generated method stubtry {while(i<10){i++;this.sleep(1000);Log.e("sjj", "i="+i);}handler1.sendEmptyMessage(123);Log.e("sjj", "sendMessage");} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}class Thread2 extends Thread{Handler handler2;@Overridepublic void run() {// TODO Auto-generated method stubsuper.run();//Looper.prepare();handler2=new Handler(){@Overridepublic void handleMessage(Message msg) {// TODO Auto-generated method stubsuper.handleMessage(msg);if(msg.what==321){Toast.makeText(MainActivity.this, "get2", Toast.LENGTH_LONG).show();}}};//Looper.loop();}}}

01-15 20:35:16.396: E/AndroidRuntime(3125): FATAL EXCEPTION: Thread-1398
01-15 20:35:16.396: E/AndroidRuntime(3125): Process: com.example.handlerdemo, PID: 3125
01-15 20:35:16.396: E/AndroidRuntime(3125): java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
01-15 20:35:16.396: E/AndroidRuntime(3125): at android.os.Handler.<init>(Handler.java:208)
01-15 20:35:16.396: E/AndroidRuntime(3125): at android.os.Handler.<init>(Handler.java:122)
01-15 20:35:16.396: E/AndroidRuntime(3125): at com.example.handlerdemo.MainActivity$Thread2$1.<init>(MainActivity.java:104)
01-15 20:35:16.396: E/AndroidRuntime(3125): at com.example.handlerdemo.MainActivity$Thread2.run(MainActivity.java:104)

调用Looper.prepare()   Looper.loop()即可

class Thread2 extends Thread{Handler handler2;@Overridepublic void run() {// TODO Auto-generated method stubsuper.run();Looper.prepare();handler2=new Handler(){@Overridepublic void handleMessage(Message msg) {// TODO Auto-generated method stubsuper.handleMessage(msg);if(msg.what==321){Toast.makeText(MainActivity.this, "get2", Toast.LENGTH_LONG).show();}}};Looper.loop();}