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); 
    } 
  }