Handlerメッセージ処理メカニズムシリーズの「01.Handlerメッセージ送信」を必ず理解する

public final boolean post(Runnable r){
       return  sendMessageDelayed(getPostMessage(r), 0);
  }
/**
@param delayMillis                     
*/
public final boolean postDelayed(Runnable r, long delayMillis){
        return sendMessageDelayed(getPostMessage(r), delayMillis);
  }
/**
        Message            ，          ，               ，                 
*/
public final boolean postAtFrontOfQueue(Runnable r){
        return sendMessageAtFrontOfQueue(getPostMessage(r));
  }
/**
@param uptimeMillis            uptimeMillis         
*/
public final boolean postAtTime(Runnable r, long uptimeMillis){
        return sendMessageAtTime(getPostMessage(r), uptimeMillis);
  }
public final boolean postAtTime(Runnable r, Object token, long uptimeMillis){
        return sendMessageAtTime(getPostMessage(r, token), uptimeMillis);
  }

private static Message getPostMessage(Runnable r) {
        Message m = Message.obtain();
        m.callback = r;
        return m;
    };
private static Message getPostMessage(Runnable r, Object token) {
        Message m = Message.obtain();
        m.obj = token;
        m.callback = r;
        return m;
    };

public final boolean sendMessage(Message msg){
        return sendMessageDelayed(msg, 0);
    };
public final boolean sendEmptyMessage(int what){
        return sendEmptyMessageDelayed(what, 0);
    };
/**
@param uptimeMillis            uptimeMillis        
*/
public final boolean sendEmptyMessageAtTime(int what, long uptimeMillis) {
        Message msg = Message.obtain();
        msg.what = what;
        return sendMessageAtTime(msg, uptimeMillis);
    };
/**
@param delayMillis                    
*/
public final boolean sendEmptyMessageDelayed(int what, long delayMillis) {
        Message msg = Message.obtain();
        msg.what = what;
        return sendMessageDelayed(msg, delayMillis);
    };
public final boolean sendMessageDelayed(Message msg, long delayMillis){
        if (delayMillis < 0) {
            delayMillis = 0;
        }
        return sendMessageAtTime(msg, SystemClock.uptimeMillis() + delayMillis);
    };
public final boolean sendMessageAtFrontOfQueue(Message msg) {
        MessageQueue queue = mQueue;
        if (queue == null) {
            RuntimeException e = new RuntimeException(
                this + " sendMessageAtTime() called with no mQueue");
            Log.w("Looper", e.getMessage(), e);
            return false;
        }
        return enqueueMessage(queue, msg, 0);
    };
 public boolean sendMessageAtTime(Message msg, long uptimeMillis) {
        MessageQueue queue = mQueue;
        if (queue == null) {
            RuntimeException e = new RuntimeException(
                    this + " sendMessageAtTime() called with no mQueue");
            Log.w("Looper", e.getMessage(), e);
            return false;
        }
        return enqueueMessage(queue, msg, uptimeMillis);
    };

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