Pageable
Purpose
"Pagination, also known as paging, is the process of dividing a document into discrete pages, either electronic pages or printed pages."
It is most common technique to manage large data set at server/client side to distribute in chunks called as pages. In todays time, Social media client apps improvised this by inventing "Infinite scroll".
Infinite scrolling allows users to load content continuously, eliminating the need for user's explicit actions. App loads some initial data and then load the rest of the data when the user reaches the bottom of the visible content. This data is divided in pages.
Basic Usage
So how do you use this library? Well, it's pretty easy. Just follow these steps..
Step 0
Create a simple PageInteractor object. PageInteractor operates on two generics types.
First generic is type of Model which TableView/CollectionView is listing.
Second generic is a type of unique items in model data for identifing duplicate entries to be filter out.
By default, the type can be given as Any, if filtering is not required or Model doesn't have any unique identifiable object.
let pageInteractor: PageInteractor<Model, Any> = PageInteractor()Step 1
Now instance of pageInteractor to be setup in ViewDidLoad() to get first page data.
func setupPageInteractor() {
// Require to provide instance of TableView/CollectionView
pageInteractor.pageDelegate = self.tableView
// NetworkManager is implementing PageableService protocol
pageInteractor.service = networkManager
pageInteractor.refreshPage()
}
override func viewDidLoad() {
super.viewDidLoad()
setupPageInteractor()
}Step 2
TableView will ask for items count from PageInteractor.
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return pageInteractor.visibleRow()
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
// Fetch a cell of the appropriate type.
if indexPath.row >= pageInteractor.count() {
let loadingCell = tableView.dequeueReusableCell(withIdentifier: "loadingCell", for: indexPath)
return loadingCell
} else {
let cell = tableView.dequeueReusableCell(withIdentifier: "cellTypeIdentifier", for: indexPath)
let cellData = pageInteractor.item(for: indexPath.row)
// Configure the cell’s contents.
cell.textLabel!.text = cellData.name
return cell
}
}
func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
pageInteractor.shouldPrefetch(index: indexPath.row)
}Step 3
Now most importent step is to provide data to PageInteractor. That is done by implementing PagableService protocol. It has got two methods in it.
protocol PagableService: class {
func loadPage<Item: Decodable>(_ page: Int, completion: @escaping (PageInfo<Item>?) -> Void)
func cancelAllRequests()
}When PageInteractor's refresh method gets called either by end of TableView load or pulling UIRefreshControl, it tracks page number and ask for next page load by calling
loadPage<Item: Decodable>(_ page: Int, completion: @escaping (PageInfo<Item>?) -> Void)
Where page indicates the next page to load. Once page gets loaded, PageInfo struct needs to be return.
struct PageInfo<T> {
var types: [T] // list of item returned from request
var page: Int // current page
var totalPageCount: Int // total page
}how it can be done, is shown below.
extension NetworkManager: PagableService {
func loadPage<Item: Decodable>(_ page: Int, completion: @escaping (PageInfo<Item>?) -> Void) {
var info: PageInfo<Item>?
getNextPage(page: page) { (response) in
// paginated response will have page number as well as total page
switch response {
case let .success(result):
// Provide PageInfo Object from the response or nil in case no response
info = PageInfo(types: result.types,
page: result.page,
totalPageCount: result.totalPageCount)
case let .failure(err):
print(err)
}
// Returning PageInfo Object from callback to PageInteractor
completion(info)
}
}
func cancelAllRequests() {
cancelAll()
}
}Advance Usage
Pageable provide additional features like
- Configurable start page index to be fetched from server
- Filtering out duplicate items while loading addition items in the list.
If server has added new entry in previous page displayed in pagination,
it results in repeat of last item in fetched new page.
Displayed __1__ On Server
____________ ____2_____
| __1__ | | __3__ | 1
| __2__ | | __4__ | 2
| __3__ | +__10__ == | __4__ | 10
|____4_____| |____5_____| 3
__5__ __6__
__6__ __7__
__7__ __8__ new fetch
__8__ __9__
In case if duplicate entries has to be filter out, It requires keypath of unique items in model data. It can be setup in initializer or later.
let pageInteractor: PageInteractor<UserModel, Int> = PageInteractor(firstPage: 1, service: networkManager, keyPath: \UserModel.id)Example
To run the example project, clone the repo, and run pod install from the Example directory first.
Requirements
Installation
Pageable is available through CocoaPods. To install it, simply add the following line to your Podfile:
pod 'Pageable'Author
mrigankgupta, [email protected]
License
Pageable is available under the MIT license. See the LICENSE file for more info.