android - FragmentStatePagerAdapter 处理 getItem() 位置

Question

我试过了，但是错误的列表被绑定(bind)到 recyclerview。我也尝试了 SparseArray，即使这样也行不通。当我启动 Mainactivity 时，getItem() 被调用两次。我如何处理退回的职位？ 我尝试返回 viewpager currentItem，即使那样也行不通。

主 Activity

public class PagerAdapter extends FragmentStatePagerAdapter {
    int mNumOfTabs;


    public PagerAdapter(android.support.v4.app.FragmentManager fragmentManager, int tabCount) 
    {
        super(fragmentManager);
        this.mNumOfTabs = tabCount;    
    } 

    @Override
    public Fragment getItem(int position) {

        return Categories_Fragment.newInstance(position);

    }

    @Override
    public int getCount() {
        return mNumOfTabs;
    }

}

类别_ fragment

public class Categories_Fragment extends Fragment 
{
private RecyclerView lvMessages; 
private int fromPage;


public static Categories_Fragment newInstance(int num) {
    Categories_Fragment f = new Categories_Fragment();

    // Supply num input as an argument.
    Bundle args = new Bundle();
    args.putInt("from", num);
    f.setArguments(args);

    return f; 
}


@Override
public void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    fromPage = getArguments().getInt("from"); 


}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {      
    // TODO Auto-generated method stub  
    View rootView = inflater.inflate(R.layout.categories_filter, container, false); 
    lvMessages    = (RecyclerView)rootView.findViewById(R.id.lv_categories_filter);

    LinearLayoutManager x =  new LinearLayoutManager(getActivity()); 
    x.setOrientation(LinearLayoutManager.VERTICAL); 

    lvMessages.setLayoutManager(x);   


    return rootView; 
}


@Override
public void onActivityCreated(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onActivityCreated(savedInstanceState);

    // bind different data to the RecyclerView based on fromPage value. 

    }

}

Answer 1

这可能是踢球者......

@Override
public void setUserVisibleHint(boolean isVisible) {
    super.setUserVisibleHint(isVisible);
    if (isVisible) {
        // bind to stuff using value of fromPage from here
    }
}

public void setUserVisibleHint (boolean isVisibleToUser) : 向系统设置一个关于此 fragment 的 UI 当前是否对用户可见的提示。此提示默认为 true，并且在 fragment 实例状态保存和恢复期间持久存在。

可能是什么问题(如果我正确理解你的问题)是寻呼机传递了它的“最后已知”位置，这并不一定意味着当前正在显示的 fragment 的位置设备屏幕。

更新:这是一个完整的示例，其中 ViewPager 处理相同的 fragment 但传递给它的数据不同:

public class ViewPagerAdapter extends FragmentStatePagerAdapter {

    private JSONArray itemsArray;
    private int fragmentId;

    public ViewPagerAdapter(JSONArray itemsArray, int fragmentId, FragmentManager manager) {
        super(manager);
        this.itemsArray = itemsArray;
        this.fragmentId = fragmentId;
    }

    @Override
    public Fragment getItem(int position) {
        JSONObject itemObject = new Listing(itemsArray, position).getObject();
        Bundle bundle = new Bundle();
        bundle.putString("item_object", itemObject.toString());
        bundle.putInt("item_position", position);
        bundle.putInt("total_items", getCount());
        bundle.putInt("fragment_Id", fragmentId);
        Fragment fragment = new ListingFragment();
        fragment.setArguments(bundle);
        return fragment;
    }

    @Override
    public int getCount() {
        return itemsArray.length();
    }

}

这是 list fragment (减去不重要的部分):

public class ListingFragment extends Fragment {

    private Listing listing;

    private String itemObject;
    private int itemPosition;
    private int totalItems;
    private int fragmentId;

    public ListingFragment() { }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Bundle bundle = getArguments();
        itemObject = bundle.getString("item_object");
        itemPosition = bundle.getInt("item_position");
        totalItems = bundle.getInt("total_items");
        fragmentId = bundle.getInt("fragment_Id");
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
        View view = ...
        // nothing special to see here, just the usual stuff
        return view;
    }

    @Override
    public void setUserVisibleHint(boolean isVisible) {
        super.setUserVisibleHint(isVisible);
        if (isVisible) {
            // send fragmentID to wherever you want to use it
            // such as your recyclerview/adapter from here
         }
     }

}

我希望这个例子能说明一些问题，我知道它对我有用。