浅析Android中的消息机制 .

public class MainActivity extends Activity implements View.OnClickListener {
    
    private TextView stateText;
    private Button btn;
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        stateText = (TextView) findViewById(R.id.tv);
        btn = (Button) findViewById(R.id.btn);
        
        btn.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        new WorkThread().start();
    }
    
    //工作线程
    private class WorkThread extends Thread {
        @Override
        public void run() {
            //......处理比较耗时的操作
            
            //处理完成后改变状态
            stateText.setText("completed");
        }
    }
}

ERROR/AndroidRuntime(421): FATAL EXCEPTION: Thread-8
ERROR/AndroidRuntime(421): android.view.ViewRoot$CalledFromWrongThreadException: 
Only the original thread that created a view hierarchy can touch its views.

public class MainActivity extends Activity implements View.OnClickListener {
    
    private static final int COMPLETED = 0;
    
    private TextView stateText;
    private Button btn;
    
    private Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            if (msg.what == COMPLETED) {
                stateText.setText("completed");
            }
        }
    };
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        stateText = (TextView) findViewById(R.id.tv);
        btn = (Button) findViewById(R.id.btn);
        
        btn.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        new WorkThread().start();
    }
    
    //工作线程
    private class WorkThread extends Thread {
        @Override
        public void run() {
            //......处理比较耗时的操作
            
            //处理完成后给handler发送消息
            Message msg = new Message();
            msg.what = COMPLETED;
            handler.sendMessage(msg);
        }
    }
}

    class WorkThread extends Thread {
          public Handler mHandler;

          public void run() {
              Looper.prepare();

              mHandler = new Handler() {
                  public void handleMessage(Message msg) {
                      // 处理收到的消息
                  }
              };

              Looper.loop();
          }
      }

/**
     * Default constructor associates this handler with the queue for the
     * current thread.
     *
     * If there isn‘t one, this handler won‘t be able to receive messages.
     */
    public Handler() {
        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 = null;
    }

/**
     * Use the provided queue instead of the default one.
     */
    public Handler(Looper looper) {
        mLooper = looper;
        mQueue = looper.mQueue;
        mCallback = null;
    }