This one worked for me:
You can add pagination with two different approaches to your List: Last item approach and Threshold item approach.
That's way this package adds two functions to RandomAccessCollection:
isLastItem
Use this function to check if the item in the current List item iteration is the last item of your collection.
isThresholdItem
With this function you can find out if the item of the current List item iteration is the item at your defined threshold. Pass an offset (distance to the last item) to the function so the threshold item can be determined.
import SwiftUI
extension RandomAccessCollection where Self.Element: Identifiable {
public func isLastItem<Item: Identifiable>(_ item: Item) -> Bool {
guard !isEmpty else {
return false
}
guard let itemIndex = lastIndex(where: { AnyHashable($0.id) == AnyHashable(item.id) }) else {
return false
}
let distance = self.distance(from: itemIndex, to: endIndex)
return distance == 1
}
public func isThresholdItem<Item: Identifiable>(
offset: Int,
item: Item
) -> Bool {
guard !isEmpty else {
return false
}
guard let itemIndex = lastIndex(where: { AnyHashable($0.id) == AnyHashable(item.id) }) else {
return false
}
let distance = self.distance(from: itemIndex, to: endIndex)
let offset = offset < count ? offset : count - 1
return offset == (distance - 1)
}
}
Examples
Last item approach:
struct ListPaginationExampleView: View {
@State private var items: [String] = Array(0...24).map { "Item \($0)" }
@State private var isLoading: Bool = false
@State private var page: Int = 0
private let pageSize: Int = 25
var body: some View {
NavigationView {
List(items) { item in
VStack(alignment: .leading) {
Text(item)
if self.isLoading && self.items.isLastItem(item) {
Divider()
Text("Loading ...")
.padding(.vertical)
}
}.onAppear {
self.listItemAppears(item)
}
}
.navigationBarTitle("List of items")
.navigationBarItems(trailing: Text("Page index: \(page)"))
}
}
}
extension ListPaginationExampleView {
private func listItemAppears<Item: Identifiable>(_ item: Item) {
if items.isLastItem(item) {
isLoading = true
/*
Simulated async behaviour:
Creates items for the next page and
appends them to the list after a short delay
*/
DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 3) {
self.page += 1
let moreItems = self.getMoreItems(forPage: self.page, pageSize: self.pageSize)
self.items.append(contentsOf: moreItems)
self.isLoading = false
}
}
}
}
Threshold item approach:
struct ListPaginationThresholdExampleView: View {
@State private var items: [String] = Array(0...24).map { "Item \($0)" }
@State private var isLoading: Bool = false
@State private var page: Int = 0
private let pageSize: Int = 25
private let offset: Int = 10
var body: some View {
NavigationView {
List(items) { item in
VStack(alignment: .leading) {
Text(item)
if self.isLoading && self.items.isLastItem(item) {
Divider()
Text("Loading ...")
.padding(.vertical)
}
}.onAppear {
self.listItemAppears(item)
}
}
.navigationBarTitle("List of items")
.navigationBarItems(trailing: Text("Page index: \(page)"))
}
}
}
extension ListPaginationThresholdExampleView {
private func listItemAppears<Item: Identifiable>(_ item: Item) {
if items.isThresholdItem(offset: offset,
item: item) {
isLoading = true
/*
Simulated async behaviour:
Creates items for the next page and
appends them to the list after a short delay
*/
DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 0.5) {
self.page += 1
let moreItems = self.getMoreItems(forPage: self.page, pageSize: self.pageSize)
self.items.append(contentsOf: moreItems)
self.isLoading = false
}
}
}
}
String Extension:
/*
If you want to display an array of strings
in the List view you have to specify a key path,
so each string can be uniquely identified.
With this extension you don't have to do that anymore.
*/
extension String: Identifiable {
public var id: String {
return self
}
}
Christian Elies, code reference
