AsyncTask#onPreExecute竟然在子线程执行？

[zhujunhua2012]

AsyncTask#onPreExecute，API说明是"Runs on the UI thread before doInBackground."，如果是在子线程中启动了此AsyncTask，log显示onPreExecute是跑在子线程里的（线程id和启动的子线程id一样），大神能给解释下？

new AsyncTask<Void, Void, Void>(){
	@Override
	protected void onPreExecute() {
	    android.util.Log.e("tag", "#onPreExecute, " + Thread.currentThread().getId());
	    super.onPreExecute();
	}
	@Override
	protected Void doInBackground(Void... params) {
	    android.util.Log.e("tag", "#doInBackground, " + Thread.currentThread().getId());
	}
	@Override
	protected void onPostExecute(Void result) {
	    android.util.Log.e("tag", "#onPostExecute, " + Thread.currentThread().getId());
	    super.onPostExecute(result);						
	}
}.execute((Void)null);

[技术小黑屋]

应该是创建AsyncTask并启动没有在主线程中，只有这样才能对后续的onPostExecute()对UI进行操作。如需了解更多地关于AsyncTask，可以看看这篇文章http://droidyue.com/blog/2014/11/08/bad-smell-of-asynctask-in-android/

[Birds2018]

AsyncTask 这个里面启动了一个线程，如果把这个东西再放到一个线程里面 就等于2个线程了。 线程id就不一样了

[heaven_wsh]

你放在子线程里启动是错误的，AsyncTask是辅助用来后台执行，然后更新UI的，只能在UI线程下启动 Threading rules There are a few threading rules that must be followed for this class to work properly: The AsyncTask class must be loaded on the UI thread. This is done automatically as of JELLY_BEAN. The task instance must be created on the UI thread. execute(Params...) must be invoked on the UI thread. http://developer.android.com/intl/zh-cn/reference/android/os/AsyncTask.html

[zhujunhua2012]

多谢，知道原因了，但是onPreExecute这个方法的API 说明有点不准确啊。。。

引用 2 楼 tiantang198707 的回复:

你放在子线程里启动是错误的，AsyncTask是辅助用来后台执行，然后更新UI的，只能在UI线程下启动 Threading rules There are a few threading rules that must be followed for this class to work properly: The AsyncTask class must be loaded on the UI thread. This is done automatically as of JELLY_BEAN. The task instance must be created on the UI thread. execute(Params...) must be invoked on the UI thread. http://developer.android.com/intl/zh-cn/reference/android/os/AsyncTask.html

[heaven_wsh]

引用 3 楼 zhujunhua_2010 的回复:

多谢，知道原因了，但是onPreExecute这个方法的API 说明有点不准确啊。。。 [quote=引用 2 楼 tiantang198707 的回复:] 你放在子线程里启动是错误的，AsyncTask是辅助用来后台执行，然后更新UI的，只能在UI线程下启动 Threading rules There are a few threading rules that must be followed for this class to work properly: The AsyncTask class must be loaded on the UI thread. This is done automatically as of JELLY_BEAN. The task instance must be created on the UI thread. execute(Params...) must be invoked on the UI thread. http://developer.android.com/intl/zh-cn/reference/android/os/AsyncTask.html

[/quote] 人家有前提要在UI线程下启动和创建，在这个前提下，文档描述是没有问题的

[CodeC]

不得违反国家法律法规

[宇宙最强皮皮虾]

[zhujunhua2012]

#onPreExecute 是在 #execute里面调用的, 所以和方法调用处在同一个线程.