问题描述
从另一个片段返回后，片段不会重新附加到其托管的 ViewPager.
A Fragment is not reattached to its hosting ViewPager after returning from another fragment.
一个 Activity 托管一个 Fragment，其布局包含一个 ViewPager(在下面的示例中为 PageListFragment).ViewPager 由 FragmentStateViewPagerAdapter 填充.分页器内托管的单个 Fragment(在下面的示例中为 PageFragment)可以打开包含一组新页面的子页面列表.
One Activity hosting a Fragment whose layout holds a ViewPager (PageListFragment in the example below). The ViewPager is populated by a FragmentStateViewPagerAdapter. The single Fragments hosted inside the pager (PageFragment in the example below) can open sub page lists, containing a new set of pages.
只要不按下后退按钮，一切都可以正常工作.一旦用户关闭其中一个子页面列表，就会重新创建先前的列表，但没有先前显示的页面.在父 PageList 上的其他页面上滑动仍然有效.
All works fine as long as the back button is not pressed. As soon as the user closes one of the sub PageLists the previous List is recreated, but without the Page that was displayed previously. Swiping through the other pages on the parent PageList still works.
可以在 github 上找到示例应用程序:
A sample application can be found on github:
public class MainActivity extends FragmentActivity {
private static final String CURRENT_FRAGMENT = MainActivity.class.getCanonicalName() + ".CURRENT_FRAGMENT";
public static final String ARG_PARENTS = "Parents";
public void goInto(String mHostingLevel, String mPosition) {
Fragment hostingFragment = newHostingFragment(mHostingLevel, mPosition);
addFragment(hostingFragment);
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
addBaseFragment();
}
private void addBaseFragment() {
Fragment hostingFragment = newHostingFragment("", "");
addFragment(hostingFragment);
}
private Fragment newHostingFragment(String mHostingLevel, String oldPosition) {
Fragment hostingFragment = new PageListFragment();
Bundle args = new Bundle();
args.putString(ARG_PARENTS, mHostingLevel + oldPosition +" > ");
hostingFragment.setArguments(args);
return hostingFragment;
}
private void addFragment(Fragment hostingFragment) {
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.fragmentSpace, hostingFragment, CURRENT_FRAGMENT);
transaction.addToBackStack(null);
transaction.commit();
}
}
PageListFragment
public class PageListFragment extends Fragment {
private String mParentString;
public PageListFragment() {
// Required empty public constructor
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_hosting, container, false);
}
@Override
public void onResume() {
mParentString = getArguments().getString(MainActivity.ARG_PARENTS);
ViewPager viewPager = (ViewPager) getView().findViewById(R.id.viewPager);
viewPager.setAdapter(new SimpleFragmentStatePagerAdapter(getFragmentManager(),mParentString));
super.onResume();
}
private static class SimpleFragmentStatePagerAdapter extends FragmentStatePagerAdapter {
private String mHostingLevel;
public SimpleFragmentStatePagerAdapter(FragmentManager fm, String hostingLevel) {
super(fm);
this.mHostingLevel = hostingLevel;
}
@Override
public android.support.v4.app.Fragment getItem(int position) {
PageFragment pageFragment = new PageFragment();
Bundle args = new Bundle();
args.putString(MainActivity.ARG_PARENTS, mHostingLevel);
args.putInt(PageFragment.ARG_POSITION, position);
pageFragment.setArguments(args);
return pageFragment;
}
@Override
public int getCount() {
return 5;
}
}
}
PageFragment
public class PageFragment extends Fragment {
public static final String ARG_POSITION = "Position";
private String mHostingLevel;
private int mPosition;
public PageFragment() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View contentView = inflater.inflate(R.layout.fragment_page, container, false);
setupTextView(contentView);
setupButton(contentView);
return contentView;
}
private void setupTextView(View contentView) {
mPosition = getArguments().getInt(ARG_POSITION);
mHostingLevel = getArguments().getString(MainActivity.ARG_PARENTS);
TextView text = (TextView) contentView.findViewById(R.id.textView);
text.setText("Parent Fragments " + mHostingLevel + "
Current Fragment "+ mPosition);
}
private void setupButton(View contentView) {
Button button = (Button) contentView.findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
openNewLevel();
}
});
}
protected void openNewLevel() {
MainActivity activity = (MainActivity) getActivity();
activity.goInto(mHostingLevel, Integer.toString(mPosition));
}
}
推荐答案
经过长时间的调查，结果证明是片段管理器的问题.
After a lengthy investigation it turns out to be a problem with the fragment manager.
当使用类似于上面的结构的片段事务将片段重新附加到页面列表时，会被悄悄丢弃.基本上与导致
When using a construct like the one above the fragment transaction to reattach the fragment to the page list is silently discarded. It is basically the same problem that causes a
java.lang.IllegalStateException: Recursive entry to executePendingTransactions
尝试更改 FragmentPager 中的片段时.
when trying to alter the fragments inside the FragmentPager.
同样的解决方案，对于这个错误的问题，也适用于这里.在构建 FragmentStatePagerAdapter 时提供正确的子片段管理器.
The same solution, as for problems with this error, is also applicable here. When constructing the FragmentStatePagerAdapter supply the correct child fragment manager.
代替
viewPager.setAdapter(new SimpleFragmentStatePagerAdapter(getFragmentManager(),mParentString));
做
viewPager.setAdapter(new SimpleFragmentStatePagerAdapter(getChildFragmentManager(),mParentString));
另见:github
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