使用RecyclerView的片段在更改方向之前不会第二次显示

Question

我有一个包含一个RecyclerView和一个按钮的片段。该片段是在按下前一个片段中的一个按钮(该按钮添加了一些数据)时提出的，回收器显示正确填充，按钮工作。然后，我回到前面的片段，再次按下按钮(添加更多数据)，同一段代码将显示相同的片段，但是RecyclerView是未填充的，该按钮无法工作。通过阅读这个question，我猜想我正在进行片段管理--因为一旦我改变了方向并重新创建了片段，列表就会显示得很好，并且按钮也能正常工作。

这就是我对碎片的管理--我是从互联网上的一个例子来的，但我担心这是不正确的。

首先，我为我的片段创建了一个基类：

public class BaseFragment extends Fragment {

    private AbstractFragmentCallback mCallback;


    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);

        try {
            mCallback = (AbstractFragmentCallback) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString()
                + " must implement " + 
AbstractFragmentCallback.class.getCanonicalName());
        }

    }

    /**
     * This method replaces the currently shown fragment with a new 
fragment of a particular class.
     * If a fragment of the required class already shown - does 
nothing.
     * @param clazz the class of the fragment to show
     * @param addToBackStack whether the replacement should be added 
to back-stack
     * @param args arguments for the newly created fragment (can be 
null)
     */
    public void replaceFragment(Class<? extends Fragment> clazz, 
boolean addToBackStack,
                            Bundle args) {
        mCallback.replaceFragment(clazz, addToBackStack, args);
    }



    public interface AbstractFragmentCallback {

        /**
         * Call to this method replaces the currently shown fragment 
with a new one
         *
         * @param clazz           the class of the new fragment
         * @param addToBackStack whether the old fragment should be 
added to the back stack
         * @param args           arguments to be set for the new fragment
         */
        void replaceFragment(Class<? extends Fragment> clazz, boolean addToBackStack,
                         Bundle args);

    }

}

因此，我的MainActivity实现了BaseFragment.AbstractfragmentCallback，因此：

public class MainActivity extends AppCompatActivity implements BaseFragment.AbstractFragmentCallback {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(....);

    if (null == savedInstanceState) {
        replaceFragment(WelcomeFragment.class, false, null);
    }
}

// ---------------------------------------------------------------------------------------------
//
// Fragments management

@Override
public void replaceFragment(Class<? extends Fragment> clazz, boolean addToBackStack,
                            Bundle args) {
    FragmentTransaction ft = getSupportFragmentManager().beginTransaction();

    Fragment newFragment;

    try {
        // Create new fragment
        newFragment = clazz.newInstance();
        if (args != null) newFragment.setArguments(args);
    } catch (InstantiationException e) {
        e.printStackTrace();
        return;
    } catch (IllegalAccessException e) {
        e.printStackTrace();
        return;
    }

    if (addToBackStack) {
        ft.addToBackStack(null);
    }

    // Change to a new fragment
    ft.replace(R.id.container, newFragment, clazz.getName());
    ft.commit();

}
// End of fragments management
//
// ---------------------------------------------------------------------------------------------

}

当我的带有按钮的片段想要打开它调用的列表片段时

replaceFragment(ListFragment.class, true, null);

因此-为了明确起见，出现了ListFragemnt，它的所有代码触发，包括重新填充RecyclerView和重新填充-我甚至看到适配器中的所有代码都在为每个项调用，但是这些项没有出现在列表中。

public class ListFragment extends BaseFragment implements ListFragmentMvc.ListViewMvcListener {

private List<MyStuff> stuffList;

@Override
public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstance) {
    stuffList = new ArrayList<>();
    return inflater.inflate(R.layout.list_activity, container, true);
}

@Override
public void onResume() {
    super.onResume();
    recyclerView = mRootView.findViewById(R.id.recycler_view);


    letsGoButton = mRootView.findViewById(R.id.lets_go_button);
    letsGoButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Activity activity = getActivity();
    if (activity != null) {
        getActivity().onBackPressed();
    }

        }
    });

    recyclerView.setItemAnimator(new DefaultItemAnimator());

    DividerItemDecoration itemDecor = new DividerItemDecoration(context, HORIZONTAL);
    recyclerView.addItemDecoration(itemDecor);

    RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(context);
    recyclerView.setLayoutManager(mLayoutManager);

    setData(MyApplication.getAllStuffItems());

}
public void setData(List<MyStuff> stuff) {
    stuffList = stuff;
    mAdapter = new StuffAdapter(stuffList);
    recyclerView.setAdapter(mAdapter);

    mAdapter.notifyDataSetChanged();
}


}

所以，在我重新进入listFragment时改变方向之前，有谁知道为什么这不起作用？

谢谢

Answer 1

哇，真是浪费了一天。

最后，我犯了几个错误，这些错误被贴在一起，互相隐藏。

我认为真正的原因是我应该

return inflater.inflate(R.layout.list_activity, container, false);

而不是

return inflater.inflate(R.layout.list_activity, container, true);

我在代码中撒了一点小谎，因为我并没有真正直接返回inflater.inflate的结果.我调用它(使用错误的参数)，然后返回null。

我想这将教会我在这篇文章中更加诚实。

Answer 2

您能否尝试将设置/更新recyclerView和letsGoButton的代码从onResume方法移到onViewCreated方法，如下所示：

@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    recyclerView = view.findViewById(R.id.recycler_view);


    letsGoButton = view.findViewById(R.id.lets_go_button);
    letsGoButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Activity activity = getActivity();
            if (activity != null) {
                getActivity().onBackPressed();
            }

        }
    });

    recyclerView.setItemAnimator(new DefaultItemAnimator());

    DividerItemDecoration itemDecor = new DividerItemDecoration(context, HORIZONTAL);
    recyclerView.addItemDecoration(itemDecor);

    RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(context);
    recyclerView.setLayoutManager(mLayoutManager);

    setData(MyApplication.getAllStuffItems());
}