片段是有趣的东西,但是,所以我想,一旦你了解了它们的怪癖,它们就是在多个设备上编写好的代码的宝贵工具。
但是,在修复方向更改错误时,我撞到了墙上。为了让我的片段工作,它需要访问属于它的视图,该视图包含 Activity 引导我进行愉快的追逐,试图找到 Activity 和 Fragment 生命周期如何交互。
我在它的onCreate()
方法中向我的活动视图添加了一个片段:
// Only add a fragment once, as after it's been added it cannot be replaced (Even though there is a .replace() method. Which is a massive gaping hole in fragments as a technology if you ask me)
if(savedInstanceState == null) {
MainMenuFragment menu= new MainMenuFragment();
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.menuFrame, menu);
transaction.commit();
}
导致此活动->片段生命周期:
01-04 15:17:27.226: W/SinglePaneActivity 0: onCreate()
01-04 15:17:27.378: W/MainMenuFragment 0: onAttach() to SinglePaneActivity 0
01-04 15:17:27.378: W/MainMenuFragment 0: onCreate()
01-04 15:17:27.453: W/MainMenuFragment 0: onActivityCreated()
01-04 15:17:27.476: W/MainMenuFragment 0: onStart()
01-04 15:17:27.476: W/SinglePaneActivity 0: onStart()
01-04 15:17:27.476: W/SinglePaneActivity 0: onResume()
01-04 15:17:27.476: W/MainMenuFragment 0: onResume()
然而,方向变化强调这通常不是这种情况,片段onCreate()
方法在它的父活动之后不会被调用onCreate()
。事实上,片段的第一个生命周期调用onAttach()
发生在 Activity 甚至被创建之前(null
作为参数传递):
01-04 15:10:49.589: W/MainMenuFragment 0: onPause()
01-04 15:10:49.589: W/SinglePaneActivity 0: onPause()
01-04 15:10:49.589: W/MainMenuFragment 0: onStop()
01-04 15:10:49.589: W/SinglePaneActivity 0: onStop()
01-04 15:10:49.589: W/MainMenuFragment 0: onDestroyView()
01-04 15:10:49.589: W/MainMenuFragment 0: onDestroy()
01-04 15:10:49.589: W/MainMenuFragment 0: onDetach()
01-04 15:10:49.609: W/SinglePaneActivity 0: onDestroy()
01-04 15:10:49.617: W/MainMenuFragment 1: onAttach() to null
01-04 15:10:49.617: W/MainMenuFragment 1: onCreate()
01-04 15:10:49.617: W/SinglePaneActivity 1: onCreate()
01-04 15:10:49.890: W/MainMenuFragment 1: onActivityCreated()
01-04 15:10:49.917: W/MainMenuFragment 1: onStart()
01-04 15:10:49.917: W/SinglePaneActivity 1: onStart()
01-04 15:10:49.921: W/SinglePaneActivity 1: onResume()
01-04 15:10:49.921: W/MainMenuFragment 1: onResume()
我完全不知道为什么会这样。任何人都可以解释为什么Fragment.onAttach()
在它包含 Activity 之前被调用?
我拥有的片段不需要访问其包含的活动(直到 UI 交互)按预期工作。