解惑Android的post()方法究竟執行在哪個執行緒中
阿新 • • 發佈:2019-02-18
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);