Question

我的应用中有4个片段，在NavActivity中管理：

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_nav);
    toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    viewPager = (ViewPager) findViewById(R.id.viewpager);
    setupViewPager(viewPager);


    fab = (FloatingActionButton) findViewById(R.id.fab);


    // Fab for fragments
    viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        }
        @Override
        public void onPageSelected(int position) {
        }

        @Override
        public void onPageScrollStateChanged(int state) {
            switch (state) {
                case ViewPager.SCROLL_STATE_DRAGGING:
                case ViewPager.SCROLL_STATE_SETTLING:
                    fab.hide(); // Hide animation
                    break;
                case ViewPager.SCROLL_STATE_IDLE:
                    switch (viewPager.getCurrentItem()) {
                        case 0:
                            fragment1.shareFab(fab); 
                        case 1:
                            fragment2.shareFab(fab); 
                            fab.setOnClickListener(new View.OnClickListener() {
                                @Override
                                public void onClick(View v) {
                                    startActivity(new Intent(NavActivity.this, MapsActivity.class));
                                }
                            });
                            break;
                        default:
                            fragment1.shareFab(null);
                            break;
                    }
                    if(viewPager.getCurrentItem() == 0 || viewPager.getCurrentItem() == 1)
                        fab.show(); // Show animation
                    break;
            }

        }
    });

    tabLayout = (TabLayout) findViewById(R.id.tabs);
    tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
        @Override
        public void onTabSelected(TabLayout.Tab tab) {
            viewPager.setCurrentItem(tab.getPosition());

        }

        @Override
        public void onTabUnselected(TabLayout.Tab tab) {

        }

        @Override
        public void onTabReselected(TabLayout.Tab tab) {

        }
    });
    tabLayout.setupWithViewPager(viewPager);
}

private void setupViewPager(ViewPager viewPager) {
    ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
    adapter.addFragment(new MainFragment(), "Main");
    adapter.addFragment(new AboutFragment(), "About");
    adapter.addFragment(new CartFragment(), "Cart");
    adapter.addFragment(new CatalogFragment(), "Catalog");
    viewPager.setAdapter(adapter);
}


///////////new class
class ViewPagerAdapter extends FragmentPagerAdapter {
    private final List<Fragment> mFragmentList = new ArrayList<>();
    private final List<String> mFragmentTitleList = new ArrayList<>();

    public ViewPagerAdapter(FragmentManager manager) {
        super(manager);
    }

    @Override
    public Fragment getItem(int position) {
        return mFragmentList.get(position);
    }

    @Override
    public int getCount() {
        return mFragmentList.size();
    }

    public void addFragment(Fragment fragment, String title) {
        mFragmentList.add(fragment);
        mFragmentTitleList.add(title);
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return mFragmentTitleList.get(position);
    }
}

@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    List<Fragment> fragments = getSupportFragmentManager().getFragments();
    if (fragments != null) {
        for (Fragment fragment : fragments) {
            fragment.onRequestPermissionsResult(requestCode, permissions, grantResults);
        }
    }
}

}

我面临一个问题，在片段之间切换后项目消失了我认为使用RecyclerView的工具和viewHolder有关。

我试图从我的服务器中抽取数据到片段C（片段编号3），数据流一切正确显示。

如果我换到碎片B（碎片编号2）或D（碎片编号4），仍然一切正常。但是，如果生病了交换到frag A（碎片号1）并返回到碎片3（我的列表项在哪里），一切都消失了，我得到了空白的屏幕，即使我上下交换，物品也不会再次下载。

这是使用我的RecyclerView的Frag num 3：

private FloatingActionButton mSharedFab;
private List<MyProducts> productsList;

//Creating Views
private RecyclerView recyclerView;
private RecyclerView.LayoutManager layoutManager;
private RecyclerView.Adapter adapter;

//Volley Request Queue
private RequestQueue requestQueue;


private int requestCount = 1;
private static final String URL_INDEX = "http://myserverip/android/product.php?page=";
//Tag values to read from json
public static final String TAG_IMAGE_URL = "product_img";
public static final String TAG_PRODUCT_SN = "product_serial_num";
public static final String TAG_PRODUCT_TITLE = "product_title";
public static final String TAG_PRODUCT_PRICE = "product_price";
public static final String TAG_PRODUCT_DESCRIPTION = "product_description";


public CartFragment() {
    // Required empty public constructor
}

 public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_cart, container, false);
    recyclerView = (RecyclerView) view.findViewById(R.id.recyclerView);
    layoutManager = new LinearLayoutManager(getActivity().getApplicationContext(), LinearLayoutManager.VERTICAL, false);
    recyclerView.setLayoutManager(layoutManager);
    recyclerView.setItemAnimator(new DefaultItemAnimator());
    recyclerView.setHasFixedSize(true);

    //Initializing our superheroes list
    productsList = new ArrayList<>();
    requestQueue = Volley.newRequestQueue(getActivity().getApplicationContext());

    //Calling method to get data to fetch data
    getData();

    //Adding an scroll change listener to recyclerview
    if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.LOLLIPOP)
    {
        recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener()
        {
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);
                if (isLastItemDisplaying(recyclerView)) {
                    getData();
                }
            }
        });
    }
    else
    {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M)
        {
            recyclerView.setOnScrollChangeListener( new RecyclerView.OnScrollChangeListener()
            {
                @Override
                public void onScrollChange(View v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) {
                    if (isLastItemDisplaying(recyclerView)) {
                        getData();
                    }
                }
            });
        }
    }

    //initializing our adapter
    adapter = new CustomAdapter(productsList, getActivity());
    //Adding adapter to recyclerview
    recyclerView.setAdapter(adapter);
    return view ;
}

和customAdapter类：

public class CustomAdapter extends RecyclerView.Adapter<CustomAdapter.ViewHolder> {

//Imageloader to load image
private ImageLoader imageLoader;
private Context context;


List<MyProducts> myProducts;

public CustomAdapter(List<MyProducts> myProducts, Context context)
{
    super();
    this.myProducts = myProducts;
    this.context = context;
}

@Override
public CustomAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View v = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.product_list, parent, false);
    ViewHolder viewHolder = new ViewHolder(v);
    return viewHolder;
}

@Override
public void onBindViewHolder(CustomAdapter.ViewHolder holder, int position) {

    if( myProducts != null) {
        MyProducts myProducts1 = myProducts.get(position);
        imageLoader = ImageVolley.getInstance(context).getImageLoader();
        imageLoader.get(myProducts1.getProductImage(), ImageLoader.getImageListener(holder.imageView, R.drawable.android_store_log, android.R.drawable.ic_dialog_alert));

        //Showing data to the views
        holder.imageView.setImageUrl(myProducts1.getProductImage(), imageLoader);
        holder.textViewProductTitle.setText(myProducts1.getProductTitle());
        holder.textViewProductDescription.setText(myProducts1.getProductDescription());
        holder.textViewProductSerialNumber.setText(myProducts1.getProductSn());
        holder.textViewProductPrice.setText(myProducts1.getProductPrice());
    }
}

@Override
public int getItemCount() {
    return myProducts.size();
}

public class ViewHolder extends RecyclerView.ViewHolder {

    //Views
    public NetworkImageView imageView;
    public TextView textViewProductTitle;
    public TextView textViewProductDescription;
    public TextView textViewProductSerialNumber;
    public TextView textViewProductPrice;

    //Initializing Views
    public ViewHolder(View itemView) {
        super(itemView);
        imageView = (NetworkImageView) itemView.findViewById(R.id.imageViewHero);
        textViewProductTitle = (TextView) itemView.findViewById(R.id.textViewProductTitle);
        textViewProductDescription = (TextView) itemView.findViewById(R.id.textViewProductDescription);
        textViewProductSerialNumber = (TextView) itemView.findViewById(R.id.textViewProductSerialNumber);
        textViewProductPrice = (TextView) itemView.findViewById(R.id.textViewProductPrice);
    }
}

Answer 1

试试这个：

viewPager.setOffscreenPageLimit(3);

将处于空闲状态的视图层次结构中当前页面任一侧应保留的页数设置为空闲状态。超出此限制的页面将在需要时从适配器重新创建。

setOffscreenPageLimit

在片段之间切换后，RecyclerView项目消失

1 个答案: