我在使用FragmentStatePagerAdapter在 fragment 内部正确显示 fragment 时遇到问题。第一次，一切正常加载，但是下次， View 为空白。我尝试了this和this答案，但不能解决问题。
所以基本上我有一个FriendActivityFragment，它被加载到MainActivity内部:
public class FriendActivityFragment extends Fragment {
private FriendsTabsPagerAdapter mAdapter;
private ViewPager mPager;
private SlidingTabLayout mTabs;
public FriendActivityFragment() {
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (mAdapter == null) {
//mAdapter = new FriendsTabsPagerAdapter(getActivity().getSupportFragmentManager());
mAdapter = new FriendsTabsPagerAdapter(getChildFragmentManager());
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.activity_friend, container, false);
super.onCreate(savedInstanceState);
mPager = (ViewPager) view.findViewById(R.id.pager);
mPager.setAdapter(mAdapter);
mTabs = (SlidingTabLayout) view.findViewById(R.id.tabs);
mTabs.setDistributeEvenly(true);
mTabs.setSelectedIndicatorColors(getResources().getColor(R.color.red));
mTabs.setBackgroundColor(getResources().getColor(R.color.theme_color));
mTabs.setViewPager(mPager);
return view;
}
@Override
public void onResume() {
super.onResume();
mAdapter.notifyDataSetChanged();
}
}
在此 fragment 内，我设置了FragmentStatePagerAdapter，如下所示:
public class FriendsTabsPagerAdapter extends FragmentStatePagerAdapter {
// Tab titles
private String[] tabs = { "Friends", "Requests" };
private FriendsListFragment[] mFragments;
public FriendsTabsPagerAdapter(FragmentManager fm) {
super(fm);
mFragments = new FriendsListFragment[tabs.length];
}
@Override
public CharSequence getPageTitle(int position) {
return tabs[position];
}
@Override
public Fragment getItem(int position) {
if (mFragments[position] == null) {
mFragments[position] = FriendsListFragment.getInstance(position);
}
return mFragments[position];
}
@Override
public int getCount() {
// get item count - equal to number of tabs
return 2;
}
@Override
public Parcelable saveState() {
return null;
}
}
然后，我加载另一个 fragment FriendsListFragment，其中listView是:
public class FriendsListFragment extends Fragment {
private View parentView;
private ListView listView;
private FriendListAdapter mAdapter;
private TextView noFriends;
public static FriendsListFragment getInstance(int position) {
FriendsListFragment friendsListFragment = new FriendsListFragment();
Bundle args = new Bundle();
args.putInt("position", position);
friendsListFragment.setArguments(args);
return friendsListFragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
parentView = inflater.inflate(R.layout.fragment_friend_list, container, false);
listView = (ListView) parentView.findViewById(R.id.listView);
noFriends = (TextView) parentView.findViewById(R.id.noFriends);
return parentView;
}
@Override
public void onResume() {
super.onResume();
parentView.findViewById(R.id.avloadingIndicatorView).setVisibility(View.VISIBLE);
initView();
}
@SuppressLint("NewApi")
@SuppressWarnings("deprecation")
public void initView() {
QueryAPI query = new QueryAPI();
Bundle bundle = getArguments();
final int pos = bundle.getInt("position");
if (bundle != null) {
switch (pos) {
case 0:
// Friend List
listView.setVisibility(View.VISIBLE);
parentView.findViewById(R.id.avloadingIndicatorView).setVisibility(View.VISIBLE);
query.friendList(new QueryAPI.ApiResponse<List<ModelFriend>>() {
@Override
public void onCompletion(List<ModelFriend> result) {
parentView.findViewById(R.id.avloadingIndicatorView).setVisibility(View.GONE);
if (result != null && !result.isEmpty()) {
if (mAdapter == null) {
mAdapter = new FriendListAdapter(getActivity(), R.layout.fragment_friend_list_item, result);
}
listView.setAdapter(mAdapter);
mAdapter.notifyDataSetChanged();
} else {
noFriends.setVisibility(View.VISIBLE);
}
}
});
break;
case 1:
// Friend Requests
parentView.findViewById(R.id.avloadingIndicatorView).setVisibility(View.VISIBLE);
query.friendRequestList(new QueryAPI.ApiResponse<List<ModelUser>>() {
@Override
public void onCompletion(List<ModelUser> result) {
parentView.findViewById(R.id.avloadingIndicatorView).setVisibility(View.GONE);
if (result != null && !result.isEmpty()) {
FriendRequestListAdapter adapter = new FriendRequestListAdapter(getActivity(), R.layout.fragment_friend_list_item, result);
listView.setAdapter(adapter);
adapter.notifyDataSetChanged();
} else {
noFriends.setText("No friend request.");
noFriends.setVisibility(View.VISIBLE);
}
}
});
break;
}
}
}
}
知道可能是什么问题吗？
编辑:崩溃日志，如果我返回
super.saveState();03-14 13:50:29.965 12418-12418/com.kalianey.oxapp E/FragmentManager: Fragment no longer exists for key f0: index 0
03-14 13:50:29.965 12418-12418/com.kalianey.oxapp E/FragmentManager: Activity state:
03-14 13:50:29.965 12418-12418/com.kalianey.oxapp D/FragmentManager: Active Fragments in 53f7ca48:
03-14 13:50:29.965 12418-12418/com.kalianey.oxapp D/FragmentManager: #0: null
03-14 13:50:29.965 12418-12418/com.kalianey.oxapp D/FragmentManager: #1: null
03-14 13:50:29.965 12418-12418/com.kalianey.oxapp D/FragmentManager: Added Fragments:
03-14 13:50:29.965 12418-12418/com.kalianey.oxapp D/FragmentManager: #0: FriendsListFragment{53dde390}
03-14 13:50:29.965 12418-12418/com.kalianey.oxapp D/FragmentManager: #1: FriendsListFragment{53dde4dc}
03-14 13:50:29.965 12418-12418/com.kalianey.oxapp D/FragmentManager: FragmentManager misc state:
03-14 13:50:29.965 12418-12418/com.kalianey.oxapp D/FragmentManager: mHost=null
03-14 13:50:29.965 12418-12418/com.kalianey.oxapp D/FragmentManager: mContainer=null
03-14 13:50:29.965 12418-12418/com.kalianey.oxapp D/FragmentManager: mCurState=0 mStateSaved=true mDestroyed=true
03-14 13:50:29.965 12418-12418/com.kalianey.oxapp D/FragmentManager: mAvailIndices: [0, 1]
03-14 13:50:29.965 12418-12418/com.kalianey.oxapp D/AndroidRuntime: Shutting down VM
03-14 13:50:29.965 12418-12418/com.kalianey.oxapp W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0xa4ce9b20)
03-14 13:50:29.965 12418-12418/com.kalianey.oxapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.kalianey.oxapp, PID: 12418
java.lang.IllegalStateException: Fragment no longer exists for key f0: index 0
at android.support.v4.app.FragmentManagerImpl.getFragment(FragmentManager.java:673)
at android.support.v4.app.FragmentStatePagerAdapter.restoreState(FragmentStatePagerAdapter.java:211)
at android.support.v4.view.ViewPager.onRestoreInstanceState(ViewPager.java:1319)
at android.view.View.dispatchRestoreInstanceState(View.java:12799)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2637)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2643)
at android.view.View.restoreHierarchyState(View.java:12777)
at android.support.v4.app.Fragment.restoreViewState(Fragment.java:471)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1105)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1259)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1624)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
03-14 13:55:30.165 12418-12418/? I/Process: Sending signal. PID: 12418 SIG: 9
最佳答案
几周前我遇到了这个问题，并且FragmentStatePagerAdapter中的saveState()或restoreState()总是有问题，因此我理解为什么您尝试在saveState()中返回null。
首先，我建议您使用FragmentPagerAdapter而不是FragmentStatePagerAdapter，并将其添加到您的适配器中:
@Override
public int getItemPosition(Object object) {
return PagerAdapter.POSITION_NONE;
}
如果对您不起作用，也许您想直接从PageAdapter继承创建自己的PageAdapter，然后将FragmentPagerAdapter的代码复制到您的PageAdapter中。如果您坚持使用restoreState()和saveState()，则只需按照FragmentStatePagerAdapter进行调试即可。
这似乎很麻烦，但是实现了PageAdapter之后，我再也不会担心有关viewpage和fragment的任何疑问。