Paging library data source with specific page index

Question

Regarding the paging library in the arch. components

It has three different datasources:

1. PageKeyedDataSource: When a request requires next/previous index keys.
2. ItemKeyedDataSource: When a request requires an item as a key.
3. PositionalDataSource: When a request requires an index to fetch next batch.

Which one to use if the backend response doesn't support next/previous index keys but only current page. when the response is as follow :

{
    "status": "success",
    "response": "1",
    "message": "Data fetched successfully",
    "data": {
        "total": 2,
        "per_page": "5",
        "page": 1,
        "items": [],
        "last_page": 1,
        "has_more": false
    }
}

Answer 1

This looks a lot like the StackOverflow response I've used in this sample.

{
  "items": [
  ],
  "has_more": true,
  "quota_max": 10000,
  "quota_remaining": 9965
}

The retrofit interface I used looks like this:

@Headers("Content-Type: application/json", "Accept: application/json")
    @GET("/2.2/users")
    fun getTopUsers(
            @Query("page") page: Int,
            @Query("pagesize") pagesize: Int,
            @Query("order") order: String = "desc",
            @Query("sort") sort: String = "reputation",
            @Query("site") site: String = "stackoverflow"

    ): Single<SOResponse<User>>

So we can specify the page size and the number of the page, like in your case.

For this I used a PageKeyedDataSource<Int, User>. Where you specify the page you want to load by passing an integer. For example, my load initial method looks like this:

override fun loadInitial(params: LoadInitialParams<Int>, callback: LoadInitialCallback<Int, User>) {
        loadState.onNext(NetworkState.LOADING)
        val disposable = soApi.apiService.getTopUsers(1, params.requestedLoadSize)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe({
                    callback.onResult(it.items, 1, 2)
                    loadState.onNext(NetworkState.LOADED)
                }, {
                    loadState.onNext(NetworkState.error(it.message))
                })

        disposables.add(disposable)
    }

If you check the callback.onResult(it.items, 1, 2) you'll see that I'm requesting the next page, which is 2.

For the other pages, I'm using this:

override fun loadAfter(params: LoadParams<Int>, callback: LoadCallback<Int, User>) {
        loadState.onNext(NetworkState.LOADING)
        val disposable = soApi.apiService.getTopUsers(params.key, params.requestedLoadSize)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe({
                    callback.onResult(it.items, params.key + 1)
                    loadState.onNext(NetworkState.LOADED)
                }, {
                    loadState.onNext(NetworkState.error(it.message))
                })
        disposables.add(disposable)
    }

This time I'm just incrementing the page number callback.onResult(it.items, params.key + 1)