69 lines
1.9 KiB
Swift
69 lines
1.9 KiB
Swift
//
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// ListBatchFetchViewModel.swift
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// Mastodon
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//
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// Created by Cirno MainasuK on 2021-11-10.
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//
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import UIKit
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import Combine
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// ref: Texture.ASBatchFetchingDelegate
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final class ListBatchFetchViewModel {
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var disposeBag = Set<AnyCancellable>()
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// timer running on `common` mode
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let timerPublisher = Timer.publish(every: 30.0, on: .main, in: .common)
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.autoconnect()
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.share()
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.eraseToAnyPublisher()
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// input
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private(set) weak var scrollView: UIScrollView?
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let hasMore = CurrentValueSubject<Bool, Never>(true)
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// output
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let shouldFetch = PassthroughSubject<Void, Never>()
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init() {
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Publishers.CombineLatest(
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hasMore,
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timerPublisher
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)
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.sink { [weak self] hasMore, _ in
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guard let self = self else { return }
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guard hasMore else { return }
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guard let scrollView = self.scrollView else { return }
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// skip trigger if user interacting
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if scrollView.isDragging || scrollView.isTracking { return }
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// send fetch request
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if scrollView.contentSize.height < scrollView.frame.height {
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self.shouldFetch.send()
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} else {
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let frame = scrollView.frame
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let contentOffset = scrollView.contentOffset
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let contentSize = scrollView.contentSize
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let visibleBottomY = contentOffset.y + frame.height
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let offset = 2 * frame.height
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let fetchThrottleOffsetY = contentSize.height - offset
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if visibleBottomY > fetchThrottleOffsetY {
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self.shouldFetch.send()
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}
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}
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}
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.store(in: &disposeBag)
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}
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}
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extension ListBatchFetchViewModel {
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func setup(scrollView: UIScrollView) {
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self.scrollView = scrollView
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}
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}
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