Android 每次更改方向后都重新创建碎片,无法恢复状态
更新:事实证明问题来自其他地方。感谢@Luksprog指出我忽略的东西Android 每次更改方向后都重新创建碎片,无法恢复状态,android,android-fragments,android-configchanges,Android,Android Fragments,Android Configchanges,更新:事实证明问题来自其他地方。感谢@Luksprog指出我忽略的东西 该项目是使用Android Studio的导航抽屉模式创建的。抽屉在NavigationDrawerFragment类中实现 当选择抽屉中的特定项目时,会添加保存视图寻呼机的片段。代码是在我的家庭活动中实现的 当屏幕旋转时,将调用NavigationDrawerFragment的onCreate() 这里是出错的地方-在重新创建时,NavigationDrawerFragment将再次调用selectItem(),这将触发我
NavigationDrawerFragment
类中实现李>
NavigationDrawerFragment
的onCreate()
NavigationDrawerFragment
将再次调用selectItem(),这将触发我的菜单项selected处理程序。这会导致Android还原ListFragment无论出于何种原因(例如方向更改)重新创建活动时,我希望保留
ViewPager
的最后一个查看页面索引
ViewPager
位于一个Fragment
(名为ListFragment
)中,该片段附加到活动。我使用的是compat库,因此片段是android.support.v4.app.fragment的子类
我认为可以通过重写onSaveInstanceState()
方法并在onCreate()
中添加适当的逻辑来实现,如下所述:
要正确处理重新启动,您的活动
在正常的活动生命周期中恢复其以前的状态
哪一个Android在破坏您的应用程序之前调用onSaveInstanceState()
活动,以便保存有关应用程序状态的数据。你
然后可以在onCreate()或
onRestoreInstanceState()
但碎片的情况似乎有所不同。当我从这个ListFragment
导航到另一个活动并按下“后退”键时,页面索引可以正确恢复。但是,当我旋转设备时,页面索引将丢失
我添加了一些日志以查看问题所在。从日志中,我发现尽管正确调用了ListFragment
(我将其称为ListFragment A)的onSaveInstanceState()
,但该特定片段类不再显示在活动中。当方向改变并且重新创建活动时,Android会调用onSaveInstanceState()
,然后调用onDetach()
,以分离此片段。然后,Android创建一个新的ListFragment
(我称之为ListFragment B)实例,并将其附加到新的旋转活动。此ListFragment B向构造函数传递了一个空的savedInstanceState
,因此最后一页索引(以及片段A的savedInstanceState中的任何配置)将丢失
事实上,每次屏幕旋转时,都会创建一个新的ListFragment
实例,但旧实例似乎不会被销毁。旋转设备时,我会看到如下日志:
D/ListFragment﹕ [1110257048] onSaveInstanceState() called, storing last page index 3
D/ListFragment﹕ [1109835992] onSaveInstanceState() called, storing last page index 0
D/ListFragment﹕ [1108826176] onSaveInstanceState() called, storing last page index 0
D/ListFragment﹕ [1108083096] onSaveInstanceState() called, storing last page index 0
D/ListFragment﹕ [1106541040] onSaveInstanceState() called, storing last page index 0
D/ListFragment﹕ [1108316656] onSaveInstanceState() called, storing last page index 0
D/ListFragment﹕ [1109134136] onSaveInstanceState() called, storing last page index 0
D/ListFragment﹕ [1108630992] onSaveInstanceState() called, storing last page index 0
D/ListFragment﹕ [1108592888] onSaveInstanceState() called, storing last page index 0
D/ListFragment﹕ [1109729064] onSaveInstanceState() called, storing last page index 0
D/ListFragment﹕ [1110257048] onDestroy()
D/ListFragment﹕ [1110257048] onDetach()
D/ListFragment﹕ [1109835992] onDestroy()
D/ListFragment﹕ [1109835992] onDetach()
D/ListFragment﹕ [1108826176] onDestroy()
D/ListFragment﹕ [1108826176] onDetach()
D/ListFragment﹕ [1108083096] onDestroy()
D/ListFragment﹕ [1108083096] onDetach()
D/ListFragment﹕ [1106541040] onDestroy()
D/ListFragment﹕ [1106541040] onDetach()
D/ListFragment﹕ [1108316656] onDestroy()
D/ListFragment﹕ [1108316656] onDetach()
D/ListFragment﹕ [1109134136] onDestroy()
D/ListFragment﹕ [1109134136] onDetach()
D/ListFragment﹕ [1108630992] onDestroy()
D/ListFragment﹕ [1108630992] onDetach()
D/ListFragment﹕ [1108592888] onDestroy()
D/ListFragment﹕ [1108592888] onDetach()
D/ListFragment﹕ [1109729064] onDestroy()
D/ListFragment﹕ [1109729064] onDetach()
D/ListFragment﹕ [1110903656] onAttach()
D/ListFragment﹕ [1110903656] onCreate()
D/ListFragment﹕ [1110903656] savedInstanceState is not NULL.
D/ListFragment﹕ [1110903656] Retrieving last page index 3
D/ListFragment﹕ [1110905248] onAttach()
D/ListFragment﹕ [1110905248] onCreate()
D/ListFragment﹕ [1110905248] savedInstanceState is not NULL.
D/ListFragment﹕ [1110905248] Retrieving last page index 0
D/ListFragment﹕ [1110906440] onAttach()
D/ListFragment﹕ [1110906440] onCreate()
D/ListFragment﹕ [1110906440] savedInstanceState is not NULL.
D/ListFragment﹕ [1110906440] Retrieving last page index 0
D/ListFragment﹕ [1110907632] onAttach()
D/ListFragment﹕ [1110907632] onCreate()
D/ListFragment﹕ [1110907632] savedInstanceState is not NULL.
D/ListFragment﹕ [1110907632] Retrieving last page index 0
D/ListFragment﹕ [1110908824] onAttach()
D/ListFragment﹕ [1110908824] onCreate()
D/ListFragment﹕ [1110908824] savedInstanceState is not NULL.
D/ListFragment﹕ [1110908824] Retrieving last page index 0
D/ListFragment﹕ [1110910016] onAttach()
D/ListFragment﹕ [1110910016] onCreate()
D/ListFragment﹕ [1110910016] savedInstanceState is not NULL.
D/ListFragment﹕ [1110910016] Retrieving last page index 0
D/ListFragment﹕ [1110911208] onAttach()
D/ListFragment﹕ [1110911208] onCreate()
D/ListFragment﹕ [1110911208] savedInstanceState is not NULL.
D/ListFragment﹕ [1110911208] Retrieving last page index 0
D/ListFragment﹕ [1110912400] onAttach()
D/ListFragment﹕ [1110912400] onCreate()
D/ListFragment﹕ [1110912400] savedInstanceState is not NULL.
D/ListFragment﹕ [1110912400] Retrieving last page index 0
D/ListFragment﹕ [1110913592] onAttach()
D/ListFragment﹕ [1110913592] onCreate()
D/ListFragment﹕ [1110913592] savedInstanceState is not NULL.
D/ListFragment﹕ [1110913592] Retrieving last page index 0
D/ListFragment﹕ [1110914784] onAttach()
D/ListFragment﹕ [1110914784] onCreate()
D/ListFragment﹕ [1110914784] savedInstanceState is not NULL.
D/ListFragment﹕ [1110914784] Retrieving last page index 0
D/HomeActivity﹕ fragment updated
D/ListFragment﹕ [1110914784] onCreateView()
D/ListFragment﹕ [1111031048] onAttach()
D/HomeActivity﹕ Fragment attached.
D/ListFragment﹕ [1111031048] onCreate()
D/ListFragment﹕ [1111031048] savedInstanceState is NULL.
D/ListFragment﹕ [1111031048] onCreateView()
D/ListFragment﹕ [1111031048] onResume(), restoring page index 0
这是我旋转屏幕大约10次后的日志。标记中的数字是类“hashCode()
。以上几行显示,先前创建的片段的onSaveInstanceState()
和onCreate()
即使被最新的片段(1111031048)替换,仍然会被调用
注意,我没有在fragment类中调用setRetainInstance()
。事实上,我尝试了setRetainInstance(false)
和setRetainInstance(true)
,但没有改变任何事情
我做错什么了吗?我可以理解需要重新创建ListFragment
,但为什么savedInstanceState
为空?如果这是预期的行为,那么解决我的需求的正确方法是什么,即在配置更改时保持页面索引
应该可以将页面索引设置为静态类变量,但我不确定它是否真的解决了问题,或者只是隐藏了它(因为我在上面的日志中发现内存泄漏) 尝试在此处使用
onCreateView()
而不是onCreate()
,这是特定于片段的,可能会有所不同
重写onSaveInstanceState()
以存储您的状态,并使用savedInstanceState.get*()
在onCreateView()中恢复它。我们在应用程序中就是这样做的,而且应该是这样。正如@Ari提到的,确保调用super.onSaveInstanceState(outState)
如问题中所述,这一问题已得到解决,再次感谢@Luksprog指出了我忽略的内容
片段
的行为实际上与活动
类一致
以下是我的问题的原因:
- 该项目是使用Android Studio的“创建项目”向导提供的导航抽屉模式创建的。抽屉在
NavigationDrawerFragment
类中实现
- 当选择抽屉中的特定项目时,会添加保存视图寻呼机的片段。代码是在我的家庭活动中实现的
- 当屏幕旋转时,将调用
NavigationDrawerFragment
的onCreate()
- 这里是问题所在-在重新创建时,
NavigationDrawerFragment
将再次调用selectItem()
,这将触发我的菜单项selected处理程序。这将导致替换ListFragment
通过在“我的菜单选择处理程序代码”中检查活动菜单项,或禁用该selectItem()
调用,可以防止出现这种情况 尽管答案已经被接受,但让我进一步澄清一下:“问题”在Android Studio模板中。正如Edmund指出的,问题在于导航抽屉中调用
class MyFragment extends ListFragment {
@Override
public void onSaveInstanceState(Bundle outState) {
outState.putString(ARG_PAGE, page);
super.onSaveInstanceState(outState);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
if(savedInstanceState != null){
if(savedInstanceState.containsKey(ARG_PAGE)){
page = savedInstanceState.getInteger(ARG_PAGE);
}
}
}
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Read in the flag indicating whether or not the user has demonstrated awareness of the
// drawer. See PREF_USER_LEARNED_DRAWER for details.
SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(getActivity());
mUserLearnedDrawer = sp.getBoolean(PREF_USER_LEARNED_DRAWER, false);
if (savedInstanceState != null) {
mCurrentSelectedPosition = savedInstanceState.getInt(STATE_SELECTED_POSITION);
mFromSavedInstanceState = true;
}
// Select either the default item (0) or the last selected item.
selectItem(mCurrentSelectedPosition);
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Read in the flag indicating whether or not the user has demonstrated awareness of the
// drawer. See PREF_USER_LEARNED_DRAWER for details.
SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(getActivity());
mUserLearnedDrawer = sp.getBoolean(PREF_USER_LEARNED_DRAWER, false);
if (savedInstanceState != null) {
mCurrentSelectedPosition = savedInstanceState.getInt(STATE_SELECTED_POSITION);
mFromSavedInstanceState = true;
} else {
// Select either the default item (0) or the last selected item.
selectItem(mCurrentSelectedPosition);
}
}
<activity android:name=".MainActivity"
android:configChanges="orientation|screenSize">
</activity>
private void openFragment(Fragment fragment, String tag) {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
Fragment existingFragment = fragmentManager.findFragmentByTag(tag);
if (existingFragment != null) {
fragmentTransaction.add(R.id.container, fragment, tag);
fragmentTransaction.commit();
}
}