此处getItemCount()不为空，但此处getlayoutmanager为空。请帮我解决这个问题。当用户在滚动结束时向下滚动recyclerview时，我正在尝试加载更多数据，以此类推。该错误发生在适配器中。
这里getLayoutManager()为空：
final GridLayoutManager gridLayoutManager = (GridLayoutManager) recyclerView.getLayoutManager();
我的适配器代码：
public class ImageAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
private Context mCtx;
private ImageView link;
private boolean isLoading;
private List<Image> imageList;
private int visibleThreshold = 5;
private final int VIEW_TYPE_ITEM = 0;
private final int VIEW_TYPE_LOADING = 1;
private int lastVisibleItem, totalItemCount;
private OnLoadMoreListener onLoadMoreListener;
public ImageAdapter(RecyclerView recyclerView, List<Image> imageList, Context mCtx) {
this.imageList = imageList;
this.mCtx = mCtx;
final GridLayoutManager gridLayoutManager = (GridLayoutManager) recyclerView.getLayoutManager();
recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
Log.d(TAG, "Tj_getItemCount" + getItemCount());
Log.d(TAG, "Tj_linearLayoutManager" + gridLayoutManager);
totalItemCount = gridLayoutManager.getItemCount();
lastVisibleItem = gridLayoutManager.findLastVisibleItemPosition();
if (!isLoading && totalItemCount <= (lastVisibleItem + visibleThreshold)) {
if (onLoadMoreListener != null) {
onLoadMoreListener.onLoadMore();
}
isLoading = true;
}
}
});
}
public void setOnLoadMoreListener(OnLoadMoreListener mOnLoadMoreListener) {
this.onLoadMoreListener = mOnLoadMoreListener;
}
@Override
public int getItemViewType(int position) {
return imageList.get(position) == null ? VIEW_TYPE_LOADING : VIEW_TYPE_ITEM;
}
@NonNull
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (viewType == VIEW_TYPE_ITEM) {
LayoutInflater inflater = LayoutInflater.from(parent.getContext());
View v = inflater.inflate(R.layout.list_items, parent, false);
ViewHolder vh = new ViewHolder(v);
return vh;
} else if (viewType == VIEW_TYPE_LOADING) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.row_loading, parent, false);
LoadingViewHolder vh1 = new LoadingViewHolder(view);
return vh1;
}
return null;
}
@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, final int position) {
if (holder instanceof ViewHolder) {
final Image image = imageList.get(position);
final String imgUrl = image.getThumb();
link.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(v.getContext(), ViewImage.class);
intent.putExtra("URL", imgUrl);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
v.getContext().startActivity(intent);
}
});
Glide.with(mCtx).load(imgUrl).into(link);
} else if (holder instanceof LoadingViewHolder) {
LoadingViewHolder loadingViewHolder = (LoadingViewHolder) holder;
loadingViewHolder.progressBar.setIndeterminate(true);
}
}
@Override
public int getItemCount() {
return imageList == null ? 0 : imageList.size();
}
public void setLoaded() {
isLoading = false;
}
private class LoadingViewHolder extends RecyclerView.ViewHolder {
public ProgressBar progressBar;
LoadingViewHolder(View view) {
super(view);
progressBar = view.findViewById(R.id.progressBar1);
}
}
class ViewHolder extends RecyclerView.ViewHolder {
ViewHolder(View v) {
super(v);
link = v.findViewById(R.id.link);
}
}
}
我的活动代码：
public class MainActivity extends AppCompatActivity {
//the URL having the json data https://api.unsplash.com/search/photos?query=canada&client_id=8b0a3f8ddb23f80f16303601c12664119e27c2d26a6fc7b43bcba68d5c35f73c
// private static final String JSON_URL = "https://api.unsplash.com/photos/random?count=25&client_id=8b0a3f8ddb23f80f16303601c12664119e27c2d26a6fc7b43bcba68d5c35f73c";
// private static final String JSON_URL = "https://api.unsplash.com/photos/?client_id=8b0a3f8ddb23f80f16303601c12664119e27c2d26a6fc7b43bcba68d5c35f73c";
int i = 2;
Image hero;
String query;
List<Image> imageList;
RecyclerView listView;
private static String JSON_URL;
private static final String TAG = "Tj";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
//initializing listview and hero list
listView = findViewById(R.id.listView);
imageList = new ArrayList<>();
Intent intent = getIntent();
query = intent.getStringExtra("category");
JSON_URL = "https://api.unsplash.com/search/photos?query=" + query + "&client_id=8b0a3f8ddb23f80f16303601c12664119e27c2d26a6fc7b43bcba68d5c35f73c&page=1";
Log.d(TAG, "Query" + JSON_URL);
loadHeroList();
}
private void loadHeroList() {
//getting the progressbar
final ProgressBar progressBar = findViewById(R.id.progressBar);
//making the progressbar visible
progressBar.setVisibility(View.VISIBLE);
//creating a string request to send request to the url
StringRequest jsonArrayRequest = new StringRequest(Request.Method.GET, JSON_URL,
new Response.Listener<String>() {
// JsonArrayRequest jsonArrayRequest = new JsonArrayRequest(
// Request.Method.GET,
// JSON_URL,
// null,
// new Response.Listener<JSONArray>() {
@Override
public void onResponse(String response) {
//hiding the progressbar after completion
progressBar.setVisibility(View.INVISIBLE);
try {
//getting the whole json object from the response
JSONObject obj = new JSONObject(response);
//we have the array named hero inside the object
//so here we are getting that json array
JSONArray heroArray = obj.getJSONArray("results");
//now looping through all the elements of the json array
for (int i = 0; i < heroArray.length(); i++) {
//getting the json object of the particular index inside the array
JSONObject jsonObject = heroArray.getJSONObject(i);
JSONObject jsonObject1 = jsonObject.getJSONObject("urls");
//creating a hero object and giving them the values from json object
hero = new Image(jsonObject.getString("id"),
jsonObject.getString("color"),
jsonObject1.getString("full"));
//adding the hero to herolist
imageList.add(hero);
}
//creating custom adapter object
final ImageAdapter adapter = new ImageAdapter(listView, imageList, getApplicationContext());
listView.setHasFixedSize(true);
// use a grid layout manager
listView.setLayoutManager(new GridLayoutManager(MainActivity.this, 2));
//adding the adapter to listview
listView.setAdapter(adapter);
adapter.setOnLoadMoreListener(new OnLoadMoreListener() {
@Override
public void onLoadMore() {
if (imageList.size() <= 20) {
imageList.add(null);
adapter.notifyItemInserted(imageList.size() - 1);
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
imageList.remove(imageList.size() - 1);
adapter.notifyItemRemoved(imageList.size());
JSON_URL = "https://api.unsplash.com/search/photos?query=" + query + "&client_id=8b0a3f8ddb23f80f16303601c12664119e27c2d26a6fc7b43bcba68d5c35f73c&page=" + i;
Log.d(TAG, "QueryLoadMore" + JSON_URL);
i++;
StringRequest jsonArrayRequest = new StringRequest(Request.Method.GET, JSON_URL,
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
//hiding the progressbar after completion
progressBar.setVisibility(View.INVISIBLE);
try {
//getting the whole json object from the response
JSONObject obj = new JSONObject(response);
//we have the array named hero inside the object
//so here we are getting that json array
JSONArray heroArray = obj.getJSONArray("results");
//now looping through all the elements of the json array
for (int i = 0; i < heroArray.length(); i++) {
//getting the json object of the particular index inside the array
JSONObject jsonObject = heroArray.getJSONObject(i);
JSONObject jsonObject1 = jsonObject.getJSONObject("urls");
//creating a hero object and giving them the values from json object
hero = new Image(jsonObject.getString("id"),
jsonObject.getString("color"),
jsonObject1.getString("full"));
//adding the hero to herolist
imageList.add(hero);
}
} catch (JSONException e) {
e.printStackTrace();
}
}
},
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
//displaying the error in toast if occurrs
Toast.makeText(getApplicationContext(), error.getMessage(), Toast.LENGTH_SHORT).show();
}
});
//creating a request queue
RequestQueue requestQueue = Volley.newRequestQueue(MainActivity.this);
//adding the string request to request queue
requestQueue.add(jsonArrayRequest);
// imageList.add(hero);
// }
adapter.notifyDataSetChanged();
adapter.setLoaded();
}
}, 5000);
} else {
Toast.makeText(MainActivity.this, "Loading data completed", Toast.LENGTH_SHORT).show();
}
}
});
} catch (JSONException e) {
e.printStackTrace();
}
}
},
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
//displaying the error in toast if occurrs
Toast.makeText(getApplicationContext(), error.getMessage(), Toast.LENGTH_SHORT).show();
}
});
//creating a request queue
RequestQueue requestQueue = Volley.newRequestQueue(this);
//adding the string request to request queue
requestQueue.add(jsonArrayRequest);
}
}
答案 0 :(得分：0)
您从未为LayoutManager设置任何类型的listView。
在创建自定义适配器对象之前，您必须设置布局管理器。
您可以通过调用以下内容进行设置：recyclerView.setLayoutManager(new GridLayoutManager(this, numberOfColumns));然后可以在您的ImageAdapter类中获取它。