如何设置RecyclerView的scrollToPositionWithOffset(x,y)？

Question

我有一个从 API 获取数据的 RecyclerView。我正在使用排球。我正在分批获取 20 个项目的数据。我希望使用线性布局管理器 myLLM.scrollToPositionWithOffset(x,y) 设置滚动位置，以便在获取下一批数据时，当前重置为顶部的滚动位置保留在上一批的最后一项。

为此，我需要在下面代码所示的位置添加以下代码行。

myLLM.scrollToPositionWithOffset(y,0);

但是我做不到。请指导我如何实现这一目标。

public class ActivityItems extends AppCompatActivity {

private RecyclerView myRvItems;
private ItemsAdapter myItemsAdapter;
private ArrayList<ItemsModel> myItemsFeedList;
private RequestQueue myRequestQueue;
private ProgressBar itemsProgressBar;
Boolean isScrolling = false;
int currentItems, totalItems, scrolledOutItems, x = 0, y = (x + 20);

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_items);

    getSupportActionBar().setTitle("Inventory Items");
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    myRvItems = findViewById(R.id.rvItems);
    itemsProgressBar = findViewById(R.id.pbItems);

    final LinearLayoutManager myLLM = new LinearLayoutManager(this);
    myRvItems.setLayoutManager(myLLM);

    myItemsFeedList = new ArrayList<>();
    myRequestQueue = Volley.newRequestQueue(this);

    parseJSON();

    myRvItems.addOnScrollListener(new RecyclerView.OnScrollListener() {
        @Override
        public void onScrollStateChanged(@NonNull RecyclerView recyclerView, int newState) {
            super.onScrollStateChanged(recyclerView, newState);
            if(newState == AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL){
                isScrolling = true;
            }
        }

        @Override
        public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);
            currentItems = myLLM.getChildCount();
            totalItems = myLLM.getItemCount();
            scrolledOutItems = myLLM.findFirstVisibleItemPosition();

            if(isScrolling && (currentItems + scrolledOutItems == totalItems)){
                isScrolling = false;
                parseJSON();
                myLLM.scrollToPositionWithOffset(4, 20);
            }
        }
    });

}

private void parseJSON() {

    itemsProgressBar.setVisibility(View.VISIBLE);
    String url = "http://restapis.xyv.com/api/list";

    JsonObjectRequest myRequest = new JsonObjectRequest(Request.Method.GET, url, null,
            new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {

                    try {
                        JSONArray myJSONArray = response.getJSONArray("Data");

                        for (int i = x; i < y && i < myJSONArray.length(); i++){

                            JSONObject myData = myJSONArray.getJSONObject(i);

                            String itemID = myData.getString("ItemID");
                            String itemName = myData.getString("ItemName");
                            String itemRackNo = myData.getString("RackNo");

                            myItemsFeedList.add(new ItemsModel(itemID,itemName,itemRackNo));

    **//   I WANT TO SET THE SCROLL POSITION HERE BUT THIS NOT WORKING**
    **//   myLLM.scrollToPositionWithOffset(y,0);**

                        }

                        myItemsAdapter = new ItemsAdapter(myItemsFeedList,ActivityItems.this );
                        myRvItems.setAdapter(myItemsAdapter);
                        itemsProgressBar.setVisibility(View.GONE);

                    } catch (JSONException e) {
                        e.printStackTrace();
                    }

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

    myRequestQueue.add(myRequest);

}

@Override
public boolean onSupportNavigateUp() {
    onBackPressed();
    return super.onSupportNavigateUp();
}

}

Answer 1

根据@mmmcho 的建议，问题已解决。 "Set your adapter first, even if your list is empty. Update your list when you get the data. Then call adapter.notifydatasetchanged() method."

还有一种粗略的分页方式。因此，如果有人正在寻找最简单的 RecyclerView 分页，他也可以按照代码进行操作。（只要让您的 api 数据按日期排序，效果最好。）

代码现在如下所示：

public class ActivityItems 扩展 AppCompatActivity {

private RecyclerView myRvItems;
private ItemsAdapter myItemsAdapter;
private ArrayList<ItemsModel> myItemsFeedList;
private RequestQueue myRequestQueue;
private ProgressBar itemsProgressBar;
Boolean isScrolling = false;
int currentItems, totalItems, scrolledOutItems, fetchSize = 6 , x = 0, y = (x + fetchSize);

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_items);

    getSupportActionBar().setTitle("Inventory Items");
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    myRvItems = findViewById(R.id.rvItems);
    itemsProgressBar = findViewById(R.id.pbItems);

    final LinearLayoutManager myLLM = new LinearLayoutManager(this);
    myRvItems.setLayoutManager(myLLM);

    myItemsFeedList = new ArrayList<>();
    myItemsAdapter = new ItemsAdapter(myItemsFeedList,ActivityItems.this );
    myRvItems.setAdapter(myItemsAdapter);

    myRequestQueue = Volley.newRequestQueue(this);

    parseJSON();


    myRvItems.addOnScrollListener(new RecyclerView.OnScrollListener() {
        @Override
        public void onScrollStateChanged(@NonNull RecyclerView recyclerView, int newState) {
            super.onScrollStateChanged(recyclerView, newState);
            if(newState == AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL){
                isScrolling = true;
            }
        }

        @Override
        public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);
            currentItems = myLLM.getChildCount();
            totalItems = myLLM.getItemCount();
            scrolledOutItems = myLLM.findFirstVisibleItemPosition();

            if(isScrolling && (currentItems + scrolledOutItems == totalItems)){
                isScrolling = false;
                y = x + fetchSize;
                parseJSON();

            }
        }
    });

}

private void parseJSON() {

    itemsProgressBar.setVisibility(View.VISIBLE);
    String url = "http://restapis.xyn.com/api/list";

    JsonObjectRequest myRequest = new JsonObjectRequest(Request.Method.GET, url, null,
            new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {

                    try {
                        JSONArray myJSONArray = response.getJSONArray("Data");

                        for (int i = x; i < y && i < myJSONArray.length(); i++){

                            JSONObject myData = myJSONArray.getJSONObject(i);

                            String itemID = myData.getString("ItemID");
                            String itemName = myData.getString("ItemName");
                            String itemRackNo = myData.getString("RackNo");

                            myItemsFeedList.add(new ItemsModel(itemID,itemName,itemRackNo));
                            x = x+1;
                        }

                        myItemsAdapter.notifyDataSetChanged();
                        itemsProgressBar.setVisibility(View.GONE);

                    } catch (JSONException e) {
                        e.printStackTrace();
                    }

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

    myRequestQueue.add(myRequest);

}

@Override
public boolean onSupportNavigateUp() {
    onBackPressed();
    return super.onSupportNavigateUp();
}}

如何设置RecyclerView的scrollToPositionWithOffset(x,y)？

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