FragmentStatePagerAdapter處理getItem（）位置

Question

我嘗試了這個，但錯誤的列表被綁定到recyclerview。 我也嘗試過SparseArray，即使這樣也行不通。 當我啟動Mainactivity時，getItem（）被調用兩次。 我如何處理返回的位置？ 我嘗試返回viewpager currentItem，即使這不起作用。

主要活動

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;
    }

}

Categories_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

這可能是踢球者...

@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） ： 向系統提供有關此片段的UI當前是否對用戶可見的提示。 此提示默認為true，並且在片段實例狀態保存和還原期間保持不變。

可能是什么問題（如果我正確理解你的問題）是尋呼機傳遞其“最后已知”位置，這並不一定意味着當前正在設備屏幕上顯示的片段的位置。

更新：這是一個完整的例子，ViewPager處理相同的片段但傳遞給它的數據不同：

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();
    }

}

這是清單片段（減去不重要的位）：

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
         }
     }

}

我希望這個例子有所啟發，我知道它對我有用。

Answer 2

您創建了一個名為PagerAdapter的類是可疑的，該類是一個Android抽象類。 將其重命名為MyPagerAdapter等唯一名稱。

Answer 3

getItem（）被調用兩次的原因是因為在ViewPager中為offScreenPageLimit分配了默認值。

您可以設置offScreenPageLimit為1或0使用setOffscreenPageLimit（INT限制）ViewPager類的方法，這將解決您的調用getItem（）時兩次的問題。

因此，如果調用getItem（）一次，那么您將在片段中獲得正確的位置值，您的問題將得到解決。

簽出方法定義和描述的鏈接

http://developer.android.com/reference/android/support/v4/view/ViewPager.html#setOffscreenPageLimit(int）

Answer 4

使用FragmentStatePagerAdapter ， HashMap<Integer,Demo_Fragment>

 public class ViewPagerAdapter extends FragmentStatePagerAdapter {
        List<String> mList;

        public ViewPagerAdapter(FragmentManager fm, List<String> list) {
            super(fm);
            mList = list;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            String  title = mList.get(position);
            return title;
        }

        public int getCount() {
            return mList.size();
        }

        public Fragment getItem(int position) {
            Demo_Fragment fragment = new Demo_Fragment();
            Bundle bundle = new Bundle();
            bundle.putString("text",mList.get(position));
            fragment.setArguments(bundle);
            fragment.setTags(position);
            mPageReferenceMap.put(position, fragment);

            return fragment;
        }

        public void destroyItem(ViewGroup container, int position, Object object) {
            super.destroyItem(container, position, object);
            mPageReferenceMap.remove(position);
        }

        public int getItemPosition(Object item) {
            Demo_Fragment fragment = (Demo_Fragment) item;
            int position = fragment.getTags();
            if (position >= 0) {
                return position;
            } else {
                return POSITION_NONE;
            }
        }
    }

為了獲得片段

public Demo_Fragment getFragment(int key) {
        return mPageReferenceMap.get(key);
    }

用於在addOnPageChangeListener ViewPager獲取當前片段

mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
            }

            @Override
            public void onPageSelected(int position) {
                final Demo_Fragment demo_Fragment = getFragment(mViewPager.getCurrentItem());
                final String str = mArrString.get(mViewPager.getCurrentItem());
                demo_Fragment.updateView(str);
                showDialog();
                mRunnable = new Runnable() {
                    @Override
                    public void run() {
                        randomGenerator = new Random();
                        randomInt = randomGenerator.nextInt(10000);
                        demo_Fragment.updateView(str +"\n" +randomInt+"-Updated Value");
                        hideDialog();
                    }
                };
                mHandler.postDelayed(mRunnable, 2000);


            }

            @Override
            public void onPageScrollStateChanged(int state) {
            }
        });

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