1. 程式人生 > >解惑Android的post()方法究竟執行在哪個執行緒中

解惑Android的post()方法究竟執行在哪個執行緒中

Android中我們常用的post()方法大致有兩種情況:

1.如果post方法是handler的,則Runnable執行在handler依附執行緒中,可能是主執行緒,也可能是其他執行緒

下面是Handler裡面的post方法

    /**
     * Causes the Runnable r to be added to the message queue.
     * The runnable will be run on the thread to which this handler is 
     * attached. 
     *  
     * @param r The Runnable that
will be executed. * * @return Returns true if the Runnable was successfully placed in to the * message queue. Returns false on failure, usually because the * looper processing the message queue is exiting. */ public final boolean post(Runnable r){ return
sendMessageDelayed(getPostMessage(r), 0); }

2.如果post方法是View的,則一定是執行在主執行緒中的,因為所有view都自帶一個handler,所有handler都有post方法,所以它的Runnable是執行在主執行緒中的

下面是View中的post方法

    /**
     * <p>Causes the Runnable to be added to the message queue.
     * The runnable will be run on the user interface thread.</p>
     *
     * @param
action The Runnable that will be executed. * * @return Returns true if the Runnable was successfully placed in to the * message queue. Returns false on failure, usually because the * looper processing the message queue is exiting. * * @see #postDelayed * @see #removeCallbacks */
public boolean post(Runnable action) { final AttachInfo attachInfo = mAttachInfo; if (attachInfo != null) { return attachInfo.mHandler.post(action); } // Assume that post will succeed later ViewRootImpl.getRunQueue().post(action); return true; }

例如:Imageview自帶一個handler,它有postDelayed方法,由於imageview是主執行緒上的,所以Runable是執行在主執行緒中的程式碼。

imageview.postDelayed(new Runnable() {  

        @Override  
        public void run() {  
            Intent mIntent = new Intent(MainActivity.this,  
                    SecondActivity.class);  
            startActivity(mIntent);  
            finish();  

        }  
    }, 2000);