Question

新的分页库的所有示例都使用了Room库，Room为我们创建了一个数据源。在我自己的情况下，我需要创建自定义数据源。

这是我的视图模型类中应该返回实时数据的方法。我的liveata总是返回null。

 LiveData<PagedList<ApiResult>> getData(){

    LivePagedListProvider<Integer,ApiResult> p = new LivePagedListProvider<Integer, ApiResult>() {
        @Override
        protected DataSource<Integer, ApiResult> createDataSource() {
            return new DataClass();
        }

    };

    listLiveData = p.create(0,new PagedList.Config.Builder()
            .setPageSize(5) //number of items loaded at once
            .setPrefetchDistance(0)// the distance to the end of already loaded list before new data is loaded
            .build());
    return listLiveData;
}

这是Data类

public class DataClass extends TiledDataSource<ApiResult> {

    private List<ApiResult> result = new ArrayList<>();

    @Override
    public int countItems() {
        return result.size();
    }

    @Override
    public List<ApiResult> loadRange(int startPosition, int count) {

        Call<String> call = NetworkModule.providesWebService().makeRequest();
        call.enqueue(new Callback<String>() {
            @Override
            public void onResponse(@NonNull Call<String> call, @NonNull Response<String> response) {
                Log.i(DataClass.this.getClass().getSimpleName() + " - onResponse", String.valueOf(response));
                result = parseJson(response.body());
            }

            @Override
            public void onFailure(@NonNull Call<String> call, @NonNull Throwable t) {
                Log.i(DataClass.this.getClass().getSimpleName() + " - onFailure", t.getMessage());
            }

        });

        return result;
    }

}

Answer 1

我认为这有助于：
1. countItems（）应该返回DataSource.COUNT_UNDEFINED
2. loadRange（int startPosition，int count）：您可以直接执行查询。
3.现在你可以删除结果全局变量

此外，关闭占位符：

listLiveData = p.create(0,new PagedList.Config.Builder()
        .setPageSize(5) //number of items loaded at once
        .setPrefetchDistance(10) //Must be >0 since placeholders are off
        .setEnablePlaceholders(false)
        .build());

以下是数据类的更新代码：

public class DataClass extends TiledDataSource<ApiResult> {

@Override
public int countItems() {
 return DataSource.COUNT_UNDEFINED;
}

@Override
public List<ApiResult> loadRange(int startPosition, int count) {

 Call<String> call = NetworkModule.providesWebService().makeRequest();
 Response<String> response = call.execute();
 return parseJson(response.body());
}

您可以在此处查看示例项目： https://github.com/brainail/.samples/tree/master/ArchPagingLibraryWithNetwork

Answer 2

您可以创建一个自定义数据源，通常我们构建了后端API以获取以pagenumber作为参数以返回指定页面的数据。

在这种情况下，您可以使用PageKeyedDataSource。这是使用StackOverflow API的PageKeyedDataSource示例代码。以下代码使用Retrofit从StackOverflow API获取数据。

public class ItemDataSource extends PageKeyedDataSource<Integer, Item> {

    //the size of a page that we want
    public static final int PAGE_SIZE = 50;

    //we will start from the first page which is 1
    private static final int FIRST_PAGE = 1;

    //we need to fetch from stackoverflow
    private static final String SITE_NAME = "stackoverflow";


    //this will be called once to load the initial data
    @Override
    public void loadInitial(@NonNull LoadInitialParams<Integer> params, @NonNull final LoadInitialCallback<Integer, Item> callback) {
        RetrofitClient.getInstance()
                .getApi().getAnswers(FIRST_PAGE, PAGE_SIZE, SITE_NAME)
                .enqueue(new Callback<StackApiResponse>() {
                    @Override
                    public void onResponse(Call<StackApiResponse> call, Response<StackApiResponse> response) {
                        if (response.body() != null) {
                            callback.onResult(response.body().items, null, FIRST_PAGE + 1);
                        }
                    }

                    @Override
                    public void onFailure(Call<StackApiResponse> call, Throwable t) {

                    }
                });
    }

    //this will load the previous page
    @Override
    public void loadBefore(@NonNull final LoadParams<Integer> params, @NonNull final LoadCallback<Integer, Item> callback) {
        RetrofitClient.getInstance()
                .getApi().getAnswers(params.key, PAGE_SIZE, SITE_NAME)
                .enqueue(new Callback<StackApiResponse>() {
                    @Override
                    public void onResponse(Call<StackApiResponse> call, Response<StackApiResponse> response) {

                        //if the current page is greater than one
                        //we are decrementing the page number
                        //else there is no previous page
                        Integer adjacentKey = (params.key > 1) ? params.key - 1 : null;
                        if (response.body() != null) {

                            //passing the loaded data
                            //and the previous page key 
                            callback.onResult(response.body().items, adjacentKey);
                        }
                    }

                    @Override
                    public void onFailure(Call<StackApiResponse> call, Throwable t) {

                    }
                });
    }

    //this will load the next page
    @Override
    public void loadAfter(@NonNull final LoadParams<Integer> params, @NonNull final LoadCallback<Integer, Item> callback) {
        RetrofitClient.getInstance()
                .getApi()
                .getAnswers(params.key, PAGE_SIZE, SITE_NAME)
                .enqueue(new Callback<StackApiResponse>() {
                    @Override
                    public void onResponse(Call<StackApiResponse> call, Response<StackApiResponse> response) {

                        if (response.body() != null) {
                            //if the response has next page
                            //incrementing the next page number
                            Integer key = response.body().has_more ? params.key + 1 : null; 

                            //passing the loaded data and next page value 
                            callback.onResult(response.body().items, key);
                        }
                    }

                    @Override
                    public void onFailure(Call<StackApiResponse> call, Throwable t) {

                    }
                });
    }
}

在这里您可以看到我们通过进行Retrofit调用获得了结果，然后将结果推送给了回调。

有关详细的逐步说明，请遍历此Android Paging Library Tutorial。

没有房间的寻呼图书馆

2 个答案: