Question

我有一张RecyclerView，其中有一张卡片列表，每张卡片都有一张照片。当我最初向下滚动时，屏幕外开始的卡片会在屏幕上显示时加载图像，但是屏幕上开始的卡片只有在移动到屏幕后才会加载图像。

它似乎也略显随机。上下文的Gif：https://gfycat.com/gifs/detail/accurateeducatedbaiji

gif中的最后一个例子（前3个餐厅图片没有加载）是最常见的。

ViewHolder：

public class LocationsViewHolder extends RecyclerView.ViewHolder{

private ImageView locationImage;
private TextView locationName;
private TextView locationAddress;

public LocationsViewHolder(View itemView) {
    super(itemView);

    locationName = (TextView)itemView.findViewById(R.id.location_name);
    locationAddress = (TextView)itemView.findViewById(R.id.location_address);
    locationImage = (ImageView) itemView.findViewById(R.id.location_image);
}

public void updateUI(Place place){
    locationName.setText(place.getName());
    if(place.getPhotoID() != null){
        // Log.v("IMAGE", "photoID for " + place.getName() + ": " + place.getPhotoID());
        locationImage.setImageBitmap(place.getImage());
    } else {
        locationImage.setImageResource(R.drawable.no_image);
    }
}

}

适配器：

public class LocationsAdapter extends RecyclerView.Adapter<LocationsViewHolder>{

ArrayList<Place> locations;

Context context;

GetNearbyPlacesData data;

public LocationsAdapter(ArrayList<Place> locations, Context context) {
    this.locations = locations;
    this.context = context;
    data = GetNearbyPlacesData.getInstance(context);
}

@Override
public LocationsViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View card = LayoutInflater.from(parent.getContext()).inflate(R.layout.card_location, parent, false);
    return new LocationsViewHolder(card);
}

@Override
public void onBindViewHolder(LocationsViewHolder holder, int position) {
    Place location = locations.get(position);
    holder.updateUI(location);
}

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

}

downloadPlaceImage：

    Bitmap bitmap;

public void downloadPlaceImage(String imageKey, final Place place){
    String url = buildImgURL(imageKey);

    ImageRequest imageRequest = new ImageRequest(url, new Response.Listener<Bitmap>() {
        @Override
        public void onResponse(Bitmap response) {
            bitmap = response;
            place.setImage(bitmap);
            Log.v("IMG", "downloaded image");
        }
    }, 0, 0, null, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {

        }
    });

    requestQueue.add(imageRequest);
}
}

如何在餐厅和药房之间切换： onNavigationItemSelected侦听器：

@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
    Log.v("NAV", "Navigation item selected");
    URLInfo = new Bundle();
    URLInfo.putString("radius", MAP_RADIUS);
    URLInfo.putString("location", userMarker.getPosition().latitude + "," + userMarker.getPosition().longitude);

    mMap.clear();
    switch (item.getItemId()){
        case R.id.nav_restaurant: {
            URLInfo.putString("type", "restaurant");
            placeList = data.downloadPlacesData(URLInfo);
            break;
        }
        case R.id.nav_pharmacy: {
            URLInfo.putString("type", "pharmacy");
            placeList = data.downloadPlacesData(URLInfo);
            break;
        }
        case R.id.nav_bank: {
            URLInfo.putString("type", "bank");
            placeList = data.downloadPlacesData(URLInfo);
            break;
        }
    }

    mDrawerLayout.closeDrawer(GravityCompat.START);
    return true;
}

downloadPlacesData()功能：

ArrayList<Place> placesList;

public ArrayList<Place> downloadPlacesData(Bundle bundle){
    String url = buildPlaceURL(bundle);

    placesList = new ArrayList<>();

    //TODO make more requests for the next pages of results since each page is limited to 20 places

    JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(url, null, new Response.Listener<JSONObject>() {
        @Override
        public void onResponse(JSONObject response) {
            try {
                JSONArray results = response.getJSONArray("results");
                for(int i = 0; i < results.length(); i++){
                    JSONObject main = results.getJSONObject(i);
                    JSONObject geo = main.getJSONObject("geometry");
                    JSONObject loc = geo.getJSONObject("location");
                    String placeID = main.getString("place_id");
                    String name = main.getString("name");
                    String lat = loc.getString("lat");
                    String lng = loc.getString("lng");
                    String photoID = null;

                    try {
                        if (main.getJSONArray("photos") != null) {
                            JSONArray photos = main.getJSONArray("photos");
                            photoID = photos.getJSONObject(0).getString("photo_reference");
                        }
                    }catch (JSONException e){
                        Log.v("JSON4", e.getLocalizedMessage());
                    }

                    Place place = new Place(photoID, name, placeID, Double.parseDouble(lat), Double.parseDouble(lng), context);
                    Log.v("NAME", name);

                    placesList.add(place);

                }
                onPlacesLoadedListener.placesLoaded(placesList);

            }catch (JSONException e){
                Log.v("JSON", e.getLocalizedMessage());
            }

        }
    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {

        }
    });

    requestQueue.add(jsonObjectRequest);

    return placesList;
}

placesLoaded回调并创建LocationsListFragment：

@Override
public void placesLoaded(ArrayList<Place> list) {
    Log.v("PLACES", "adding places");
    MarkerOptions markerOptions = new MarkerOptions();

    // build a resource path using the type of place
    String type = URLInfo.getString("type");
    String resourcePath = "drawable/pin_" + type;

    // create a resource path out of the String created
    int resource = getResources().getIdentifier(resourcePath, null, this.getPackageName());

    // set the marker icon according to the place type
    markerOptions.icon(BitmapDescriptorFactory.fromResource(resource));

    for(int i = 0; i < list.size(); i++){
        // get the latitude and longitude
        double lat = list.get(i).getLat();
        double lng = list.get(i).getLng();
        // set the marker position and title
        markerOptions.position(new LatLng(lat, lng));
        markerOptions.title(list.get(i).getName());
        mMap.addMarker(markerOptions);
    }
    createLocationsListFragment();

}

private void createLocationsListFragment() {
    FragmentManager fm = getSupportFragmentManager();
    LocationsListFragment fragment = LocationsListFragment.newInstance();
    fm.beginTransaction().add(R.id.container_locations, fragment).commit();
}

最后，实际片段（onCreate和onCreateView）：

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

    getLocationsData = (GetLocationsData) getContext();
    mParam1 = getLocationsData.getList();
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View v = inflater.inflate(R.layout.fragment_locations_list, container, false);
    adapter = new LocationsAdapter(mParam1, getContext());

    RecyclerView recyclerView = (RecyclerView)v.findViewById(R.id.recycler_locations);
    recyclerView.setHasFixedSize(true);
    recyclerView.setAdapter(adapter);

    LinearLayoutManager layoutManager = new LinearLayoutManager(getContext(), LinearLayoutManager.VERTICAL, false);
    recyclerView.setLayoutManager(layoutManager);

    return v;
}

Answer 1

如果您有图片的网址或位图，那么请使用滑动，如果您发送网址并加载for more about glide

，它会缓存您的图片进行网络通话

Glide.with(mContext)
    .load(imageUrl)
    .diskCacheStrategy(DiskCacheStrategy.ALL)
    .centerCrop()
    .into(mImageView_photo)
;

Answer 2

在RecyclerView中，您必须确保为每个项目返回唯一的ID，或者如果没有Stable Id，则应返回RecyclerView.NO_ID（-1）。请避免返回不稳定的值。（稳定值将是一个唯一值，即使数据集的位置发生变化也不会改变）

在您的RecyclerView适配器中添加getItemId回调。

例如：

@Override
public long getItemId(int position) {
    return Long.parseLong(programList.get(position).getLmsId());
}

RecyclerView中的图像在启动时不会出现

2 个答案: