Android Handler 原理分析及实例代码

public class MainActivity extends AppCompatActivity {   public final static String UPPER_NUM="upper_num";   private EditText editText;   public jisuanThread jisuan;   public Handler mainhandler;   private TextView textView;   class jisuanThread extends Thread{     public Handler mhandler;     @Override     public void run() {       Looper.prepare();       final ArrayList<Integer> al=new ArrayList<>();       mhandler=new Handler(){         @Override         public void handleMessage(Message msg) {            if(msg.what==0x123){             Bundle bundle=msg.getData();             int up=bundle.getInt(UPPER_NUM);             outer:             for(int i=3;i<=up;i++){               for(int j=2;j<=Math.sqrt(i);j++){                 if(i%j==0){                   continue outer;                 }               }               al.add(i);             }             Message message=new Message();             message.what=0x124;             Bundle bundle1=new Bundle();             bundle1.putIntegerArrayList("Result",al);             message.setData(bundle1);             mainhandler.sendMessage(message);           }         }       };       Looper.loop();     }   }   @Override   protected void onCreate(Bundle savedInstanceState) {     super.onCreate(savedInstanceState);     setContentView(R.layout.activity_main);     editText= (EditText) findViewById(R.id.et_num);     textView= (TextView) findViewById(R.id.tv_show);     jisuan=new jisuanThread();     jisuan.start();     mainhandler=new Handler(){       @Override       public void handleMessage(Message msg) {         if(msg.what==0x124){           Bundle bundle=new Bundle();           bundle=msg.getData();           ArrayList<Integer> al=bundle.getIntegerArrayList("Result");           textView.setText(al.toString());         }       }     };     findViewById(R.id.bt_jisuan).setOnClickListener(new View.OnClickListener() {       @Override       public void onClick(View v) {         Message message=new Message();         message.what=0x123;         Bundle bundle=new Bundle();         bundle.putInt(UPPER_NUM, Integer.parseInt(editText.getText().toString()));         message.setData(bundle);         jisuan.mhandler.sendMessage(message);       }     });   } } 

public static void loop() {     final Looper me = myLooper();     if (me == null) {       throw new RuntimeException("No Looper; Looper.prepare() wasn't called on this thread.");     }     final MessageQueue queue = me.mQueue;     // Make sure the identity of this thread is that of the local process,     // and keep track of what that identity token actually is.     Binder.clearCallingIdentity();     final long ident = Binder.clearCallingIdentity();      for (;;) {       Message msg = queue.next(); // might block       if (msg == null) {         // No message indicates that the message queue is quitting.         return;       }       // This must be in a local variable, in case a UI event sets the logger       Printer logging = me.mLogging;       if (logging != null) {         logging.println(">>>>> Dispatching to " + msg.target + " " +             msg.callback + ": " + msg.what);       }       msg.target.dispatchMessage(msg);        if (logging != null) {         logging.println("<<<<< Finished to " + msg.target + " " + msg.callback);       }       // Make sure that during the course of dispatching the       // identity of the thread wasn't corrupted.       final long newIdent = Binder.clearCallingIdentity();       if (ident != newIdent) {         Log.wtf(TAG, "Thread identity changed from 0x"             + Long.toHexString(ident) + " to 0x"             + Long.toHexString(newIdent) + " while dispatching to "             + msg.target.getClass().getName() + " "             + msg.callback + " what=" + msg.what);       }        msg.recycleUnchecked();     }   } 

private Looper(boolean quitAllowed) {     mQueue = new MessageQueue(quitAllowed);     mThread = Thread.currentThread();   } 

private static void prepare(boolean quitAllowed) {     if (sThreadLocal.get() != null) {       throw new RuntimeException("Only one Looper may be created per thread");     }     sThreadLocal.set(new Looper(quitAllowed));   } 

public Handler(Callback callback, boolean async) {     if (FIND_POTENTIAL_LEAKS) {       final Class<? extends Handler> klass = getClass();       if ((klass.isAnonymousClass() || klass.isMemberClass() || klass.isLocalClass()) &&           (klass.getModifiers() & Modifier.STATIC) == 0) {         Log.w(TAG, "The following Handler class should be static or leaks might occur: " +           klass.getCanonicalName());       }     }      mLooper = Looper.myLooper();     if (mLooper == null) {       throw new RuntimeException(         "Can't create handler inside thread that has not called Looper.prepare()");     }     mQueue = mLooper.mQueue;     mCallback = callback;     mAsynchronous = async;   } 

public static Looper myLooper() {     return sThreadLocal.get();   } 

private boolean enqueueMessage(MessageQueue queue, Message msg, long uptimeMillis) {     msg.target = this;     if (mAsynchronous) {       msg.setAsynchronous(true);     }     return queue.enqueueMessage(msg, uptimeMillis);   } 

public void dispatchMessage(Message msg) {     if (msg.callback != null) {       handleCallback(msg);     } else {       if (mCallback != null) {         if (mCallback.handleMessage(msg)) {           return;         }       }       handleMessage(msg);     }   }