使用setOnScrollListener从服务器获取仅20行

Question

这是我第一次使用onscroll监听器.我的问题是每次向下滚动时如何获取20个新行？

我理解当我向下滚动网格视图时,将执行此代码.

public void onScroll(AbsListView view, int firstVisibleItem,
                             int visibleItemCount, int totalItemCount) {
            // TODO Auto-generated method stub

            this.currentFirstVisibleItem = firstVisibleItem;
            this.currentVisibleItemCount = visibleItemCount;
            this.totalItem = totalItemCount;

            if ((totalItemCount - visibleItemCount) <= (firstVisibleItem + 20)) {
               // the below when executed will get all the rows ,I only need 20 rows
             handler.execute().get();

            }
        }

这是我的代码

// the load more in the grid view, fetch new images.
mGridView.setOnScrollListener(new AbsListView.OnScrollListener() {
    private int currentVisibleItemCount;
    private int currentScrollState;
    private int currentFirstVisibleItem;
    private int totalItem;
    private LinearLayout lBelow;

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        // TODO Auto-generated method stub
        this.currentScrollState = scrollState;
        this.isScrollCompleted();
    }

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem,
                         int visibleItemCount, int totalItemCount) {
        // TODO Auto-generated method stub

        this.currentFirstVisibleItem = firstVisibleItem;
        this.currentVisibleItemCount = visibleItemCount;
        this.totalItem = totalItemCount;

        if ((totalItemCount - visibleItemCount) <= (firstVisibleItem + 20)) {
           // load new 20 row but how to do that

        }
    }

    private void isScrollCompleted() {
        if (totalItem - currentFirstVisibleItem == currentVisibleItemCount
                && this.currentScrollState == SCROLL_STATE_IDLE) {
            Log.d("a", "poooppii");

        }
    }

    ;
});

这是连接发生的地方

 protected void showList(){
        try {

            JSONObject jsonObj = new JSONObject(myJSON);
            peoples = jsonObj.getJSONArray("result");
            System.out.println("Length:"+peoples.length());
            int J_length=peoples.length()-1;


            jsonObj= peoples.getJSONObject(J_length);


                Listitem = new ArrayList<Listitem>();

                for (int i = 0; i < peoples.length(); i++) {
                    JSONObject c = peoples.getJSONObject(i);

                    String id = c.getString("id");
                    String url = c.getString("url");

                    int intid = 0;
                    try {
                        intid = Integer.parseInt(id.toString());
                    } catch (NumberFormatException nfe) {
                        System.out.println("Could not parse " + nfe);
                    }

                    Listitem.add(new Listitem(id, url));
                    System.out.println(Listitem);
                }
            //}
            if (mListener != null)
                  mListener.myMethod(Listitem);


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

    }

Answer 1

您需要维护base和limit加载数据.初始化您的基数和限制变量.

int base = 0, limit = 20;

base加载新项目时增加变量.

base = base + limit;
handler.execute().get();

在通话中传递base和limit变量API,以便您可以在API旁边查询中使用它.

注意:base是一个值,您需要从该位置开始获取值.limit是您需要获取的行数的值.

请参阅本在sqlite的限制查询.
请参阅此提供在MySQL限制查询.
请参阅本在SQL查询的限制.

Answer 2

这是一个工作代码，请根据您的使用进行修改 -

假设以下是您的模型 -

public class MyModel {
    String name;
}

您需要一个界面 -

public interface PagingListener<T> {
    void onItemUpdate(ArrayList<T> allData);
}

像这样设计你的适配器 -

public class CouponsAdapter extends RecyclerView.Adapter<CouponsAdapter.CouponHolder> implements View.OnClickListener, PagingListener<MyModel> {
    private final static int TYPE_LOADING = 0;
    private final static int TYPE_DATA = 1;
    private FragmentActivity activity;
    private LayoutInflater inflater;
    private PagingRequestHandler<MyModel> pagingRequestHandler;
    private ArrayList<MyModel> data = null;

    public CouponsAdapter(FragmentActivity activity) {
        this.activity = activity;
        inflater = LayoutInflater.from(activity);
        this.data = new ArrayList<>();
        this.pagingRequestHandler = new PagingRequestHandler<>(data, this);
    }

    @Override
    public int getItemViewType(int position) {
        return position >= data.size() ? TYPE_LOADING : TYPE_DATA;
    }

    @Override
    public CouponHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view;
        if (viewType == TYPE_DATA) {
            view = inflater.inflate(R.layout.item_coupons_card_block, parent, false);
        } else {
            view = inflater.inflate(R.layout.item_drawer_payment_loading, parent, false);
        }
        return new CouponHolder(view, viewType);
    }

    @Override
    public void onBindViewHolder(CouponHolder holder, int position) {
        if (getItemViewType(position) == TYPE_DATA) {
            //Bind your view here
        }
        pagingRequestHandler.checkAndMakeRequestForMoreData(position); //Will check and make request
    }

    @Override
    public int getItemCount() {
        return data.size() + (pagingRequestHandler.isNoMoreDataLeft() ? 0 : 1); // If no data then it will return 1 to show loading
    }

    @Override
    public void onClick(View v) {
    }

    @Override
    public void onItemUpdate(ArrayList<MyModel> allData) {
        this.data = allData; // will update data with updated content
        notifyDataSetChanged();

    }


    public class CouponHolder extends RecyclerView.ViewHolder {
        public CouponHolder(View itemView, int itemType) {
            super(itemView);
            if (itemType == TYPE_DATA) {
            }
        }
    }
}

现在这是分页请求处理程序，它将跟踪页码并发出下一页的请求 -

public class PagingRequestHandler<T> {
    public static final int PAGE_SIZE = 10;
    private final PagingListener listener;
    private final ArrayList<MyModel> arrayList;
    private final String url = "Your Url here";
    private boolean noMoreDataLeft;
    private int pagingIndex = 0;
    private boolean requestGoingOn;


    public PagingRequestHandler(ArrayList<MyModel> data, PagingListener<MyModel> listener) {
        this.listener = listener;
        this.arrayList = data;
        fetchMoreData();

    }

    private void fetchMoreData() {
        requestGoingOn = true;
        Call<MyModel[]> getCoupons = Utils.getRetrofit().getCoupons(url + "/" + pagingIndex); // I am using retrofit for network call, you can use your own
        getCoupons.enqueue(new Callback<MyModel[]>() {
            @Override
            public void onResponse(Response<MyModel[]> response, Retrofit retrofit) {
                try {
                    requestGoingOn = false;
                    MyModel[] couponModelDses = response.body();
                    if (couponModelDses != null) {
                        for (MyModel couponModelDse : couponModelDses) {
                            arrayList.add(couponModelDse);
                        }
                        if (couponModelDses.length < PAGE_SIZE)
                            noMoreDataLeft = true;
                        listener.onItemUpdate(arrayList);
                    }
                } catch (Exception e) {
                    e.printStackTrace();

                }
            }

            @Override
            public void onFailure(Throwable t) {
                requestGoingOn = false;
            }
        });
    }

    public boolean isNoMoreDataLeft() {
        return noMoreDataLeft;
    }

    public void checkAndMakeRequestForMoreData(int position) {
        if (!noMoreDataLeft && !requestGoingOn && position > (PAGE_SIZE * pagingIndex)) {
            if ((position % PAGE_SIZE) > (int) (PAGE_SIZE * .7)) {
                pagingIndex++;
                fetchMoreData();
            }
        }
    }
}

工作原理 -适配器正在初始化处理程序，这是第一次进行网络调用。适配器现在调用处理程序 api 来检查每次 onBind 时是否滚动了 70% 的页面。现在，如果已显示 70% 的数据，则它会再次进行网络调用并使名为 requestGoingOn 的变量为 true，以便您可以在列表中显示加载程序。当请求完成时，处理程序将数据添加到 arraylist 并通过调用回调更新适配器onItemUpdate。

希望它会有所帮助，如果您需要进一步的帮助，请告诉我:)