如何在Retrofit 2.0中处理分页/加载更多内容? [英] How to handle pagination/load more in Retrofit 2.0?

问题描述

我还没有找到适当的示例，说明如何在向下滚动RecyclerView时使应用程序从Retrofit onResponse加载更多项目.

I haven't found yet the proper examples of how to make an app load more items from Retrofit onResponse while scrolling down the RecyclerView.

这是我如何装载拳头20件物品的方法:

Here is how I'm loading my fist 20 items:

List<ModelPartners> model = new ArrayList<>();

Call<ResponsePartners> call = ApiClient.getRetrofit().getPartnerList(params);
call.enqueue(this);

我的RecyclerView

My RecyclerView

PartnersAdapter adapter = new PartnersAdapter(getContext(), recyclerView, model);
recyclerView.setAdapter(adapter);

这是我的改造onResponse:

@Override
    public void onResponse(Call<ResponsePartners> call, Response<ResponsePartners> response) {
        if (getActivity() != null && response.isSuccessful()) {
            List<ModelPartners> body = response.body().getData();
            //Rest of the code to add body to my Adapter and notifyDataSetChanged
            }
        }

我的问题是，每次我添加滚动加载更多项目的方法时，onResponse都会不停地加载直到最后一页.即使我已将loading设置为 false .

My Problem is, every time I add the method to load more items on scroll, onResponse keeps loading non-stop till the last page. Even if I have put set loading to false.

有人可以显示如何在翻新中正确使用分页吗?您在Retrofit中使用了哪些库，或者向我展示了如何使用它?预先谢谢你

Can someone please show how to properly use pagination in Retrofit? What libraries you used with Retrofit or show me how you did it your way? Thank you in advance

推荐答案

您需要三件事来实现这一目标，您需要:

You need three things to achieve this, you need:

1. 您需要一个onscroll侦听器以访问回收者视图.
2. 您需要一种将新项目添加到回收站适配器的方法
3. 您需要呼叫分页端点

假设您在服务器上拥有这样的模型

Assuming you have a model like this from the server

public class PagedList<T> {

    private int page = 0;
    private List<T> results = new ArrayList<>();
    private int totalResults = 0;
    private int totalPages = 0;

    public int getPage() {
        return page;
    }

    public void setPage(int page) {
        this.page = page;
    }

    public List<T> getResults() {
        return results;
    }

    public void setResults(List<T> results) {
        this.results = results;
    }

    public int getTotalResults() {
        return totalResults;
    }

    public void setTotalResults(int totalResults) {
        this.totalResults = totalResults;
    }

    public int getTotalPages() {
        return totalPages;
    }

    public void setTotalPages(int totalPages) {
        this.totalPages = totalPages;
    }
}

您的OnScroll侦听器:- 在您的活动中，这就是您想要的，所以在活动中添加第二种方法

Your OnScroll Listener: - In your activity this is what you would have, so add the second method to your activity

public void onCreate(Bundle savedInstance) {

    // setup your view components
    // ...

    // get the layout manager
    LinearLayoutManager layoutManager = new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false);

    // rest endpoint
    apiEndpoint = retrofit.create(RetrofitEndpoint.class);

    // initialise loading state
    mIsLoading = false;
    mIsLastPage = false;

    // amount of items you want to load per page
    final int pageSize = 20;

    // set up scroll listener
    recyclerView.addOnScrollListener(new  RecyclerView.OnScrollListener() {
            @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);
            // number of visible items
            int visibleItemCount = layoutManager.getChildCount();
            // number of items in layout
            int totalItemCount = layoutManager.getItemCount();
            // the position of first visible item
            int firstVisibleItemPosition = layoutManager.findFirstVisibleItemPosition();

            boolean isNotLoadingAndNotLastPage = !mIsLoading && !mIsLastPage;
            // flag if number of visible items is at the last
            boolean isAtLastItem = firstVisibleItemPosition + visibleItemCount >= totalItemCount;
            // validate non negative values
            boolean isValidFirstItem = firstVisibleItemPosition >= 0;
            // validate total items are more than possible visible items
            boolean totalIsMoreThanVisible = totalItemCount >= pageSize;
            // flag to know whether to load more
            boolean shouldLoadMore = isValidFirstItem && isAtLastItem && totalIsMoreThanVisible && isNotLoadingAndNotLastPage

            if (shouldLoadMore) loadMoreItems(false);
        }
    });

    // load the first page
    loadMoreItems(true);
}

private void loadMoreItems(boolean isFirstPage) {
    // change loading state
    mIsLoading = true;
    mCurrentPage = mCurrentPage + 1;

    // update recycler adapter with next page
    apiEndpoint.getPagedList(mCurrentPage).enqueue(new Callback<PagedList<Object>>() {
        @Override
        public void onResponse(Call<PagedList<Object>> call, Response<PagedList<Object>> response) {
            PagedList<Object> result = response.body();

            if (result == null) return;
            else if (!isFirstPage) mAdapter.addAll(result.getResults());
            else mAdapter.setList(result.getResults());

            mIsLoading = false;
            mIsLastPage = mCurrentPage == result.getTotalPages();
        }

        @Override
        public void onFailure(Call<PagedList<Object>> call, Throwable t) {
            Log.e("SomeActivity", t.getMessage());
        }
    });
}

回收站适配器:- 对于回收站适配器，您所需要做的就是添加一种将项目添加到其列表中的方法，如下所示:

Recycler Adapter: - For the recycler adapter all you need is to add a method that adds items to its list, as below

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

    private List<Object> list;


    // .. other overridden members

    public void setList(List<Object> list) {
        this.list = list;
        notifyDataSetChanged();
    }

    public void addAll(List<Object> newList) {
        int lastIndex = list.size() - 1;
        list.addAll(newList);
        notifyItemRangeInserted(lastIndex, newList.size());
    }
}

最后，您的改造界面进入页面，如下所示:

Then finally your retrofit interface that takes the page, as below:

interface RetrofitEndpoint {

    @GET("paged/list/endpoint")
    Call<PagedList<Object>> getPagedList(@Query("page") int page);
}

希望有帮助.

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