Adds a scroll offset manager class which caches and restores scroll offsets #63
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| Original file line number | Diff line number | Diff line change |
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| // | ||
| // ScrollDelegatable.swift | ||
| // ThunderTable | ||
| // | ||
| // Created by Simon Mitchell on 02/09/2020. | ||
| // Copyright © 2020 threesidedcube. All rights reserved. | ||
| // | ||
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| import UIKit | ||
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| /// A simpler version of `UIScrollViewDelegate` so we don't intefere | ||
| /// with users `UIScrollViewDelegate` implementations | ||
| public protocol ScrollOffsetDelegate: class { | ||
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| /// Called when the content offset of the scroll view changes due to `scrollViewDidScroll` | ||
| /// - Parameters: | ||
| /// - scrollable: The scrollable that the change was for | ||
| func scrollViewDidChangeContentOffset(_ scrollable: ScrollOffsetManagable) | ||
| } | ||
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| /// A protocol implemented to allow control and listening to scroll view offset changes | ||
| /// by `ScrollOfffsetManager` | ||
| public protocol ScrollOffsetManagable: class { | ||
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| /// The scroll view that is controllable on the object | ||
| var scrollView: UIScrollView? { get } | ||
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| /// The delegate to have scroll view delegate methods passed to, this should be a `weak` | ||
| /// property to avoid retain cycles. | ||
| /// - Warning: It is your job to call the method on this delegate from your scrollViewDidScroll method. | ||
| var scrollDelegate: ScrollOffsetDelegate? { get set } | ||
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| /// An identifier used by `ScrollOffsetManager` | ||
| var identifier: AnyHashable? { get set } | ||
| } | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,75 @@ | ||
| // | ||
| // ScrollOffsetManager.swift | ||
| // ThunderTable | ||
| // | ||
| // Created by Simon Mitchell on 02/09/2020. | ||
| // Copyright © 2020 threesidedcube. All rights reserved. | ||
| // | ||
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| import CoreGraphics | ||
| import Foundation | ||
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| /// Scroll offset manager manages caching scroll offsets for UI in any scenario where | ||
| /// scroll views may be re-used and so we need to store their current offset in memory | ||
| /// to avoid re-use issues. | ||
| class ScrollOffsetManager { | ||
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| private var offsetMap: [AnyHashable : CGPoint] = [:] | ||
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| /// Registers the scrollable to the manager for listening for scroll offset changes | ||
| /// - Parameters: | ||
| /// - scrollable: The scrollable to register | ||
| func register( | ||
| scrollable: ScrollOffsetManagable | ||
| ) { | ||
| scrollable.scrollDelegate = self | ||
| } | ||
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| /// Caches the offset for the given scrollable | ||
| /// - Parameters: | ||
| /// - scrollable: The scrollable to update the content offset for | ||
| func updateCachedOffset(scrollable: ScrollOffsetManagable) { | ||
| guard let identifier = scrollable.identifier else { return } | ||
| offsetMap[identifier] = scrollable.scrollView?.contentOffset | ||
| } | ||
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| /// Sets the content offset on the given scrollable from the internal cache | ||
| /// - Parameters: | ||
| /// - scrollable: The scrollable to adjust the content offset on | ||
| /// - animated: Whether the transition should animate | ||
| /// - fallback: A fallback to set the content offset to if there is no cached value | ||
| func setScrollOffset( | ||
| _ scrollable: ScrollOffsetManagable, | ||
| animated: Bool = false, | ||
| fallback: CGPoint? = nil | ||
| ) { | ||
| guard let identifier = scrollable.identifier else { return } | ||
| guard let newOffset = offsetMap[identifier] ?? fallback else { return } | ||
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| guard let scrollView = scrollable.scrollView else { return } | ||
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| // Disable then re-enable scroll indicators otherwise calling setContentOffset flashes the scroll indicators | ||
| let preShowVerticalScrollIndicator = scrollView.showsVerticalScrollIndicator | ||
| let preShowHorizontalScrollIndicator = scrollView.showsHorizontalScrollIndicator | ||
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| scrollView.showsVerticalScrollIndicator = false | ||
| scrollView.showsHorizontalScrollIndicator = false | ||
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| scrollable.scrollView?.setContentOffset(newOffset, animated: animated) | ||
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| scrollView.showsVerticalScrollIndicator = preShowVerticalScrollIndicator | ||
| scrollView.showsHorizontalScrollIndicator = preShowHorizontalScrollIndicator | ||
| } | ||
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| /// Resets all content offsets by removing them from the offset map | ||
| func resetAllOffsets() { | ||
| offsetMap = [:] | ||
| } | ||
| } | ||
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| extension ScrollOffsetManager: ScrollOffsetDelegate { | ||
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| func scrollViewDidChangeContentOffset(_ scrollable: ScrollOffsetManagable) { | ||
| updateCachedOffset(scrollable: scrollable) | ||
| } | ||
| } | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,33 @@ | ||
| // | ||
| // CollectionTableViewCell.swift | ||
| // ThunderTableDemo | ||
| // | ||
| // Created by Simon Mitchell on 02/09/2020. | ||
| // Copyright © 2020 3SidedCube. All rights reserved. | ||
| // | ||
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| import UIKit | ||
| import ThunderTable | ||
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| class CollectionTableViewCell: UITableViewCell, ScrollOffsetManagable, UICollectionViewDelegate { | ||
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| var scrollView: UIScrollView? { | ||
| return collectionView | ||
| } | ||
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| weak var scrollDelegate: ScrollOffsetDelegate? | ||
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| var identifier: AnyHashable? | ||
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| @IBOutlet weak var collectionView: UICollectionView! | ||
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| override func awakeFromNib() { | ||
| super.awakeFromNib() | ||
| collectionView.register(CollectionViewCell.self, forCellWithReuseIdentifier: "Cell") | ||
| collectionView.delegate = self | ||
| } | ||
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| func scrollViewDidScroll(_ scrollView: UIScrollView) { | ||
| scrollDelegate?.scrollViewDidChangeContentOffset(self) | ||
| } | ||
| } |
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I can defo see why if the implementor providing an identifier is real nice. Hence this. But it's a little annoying to have to provide it. Maybe I'm overlooking here, how's this going to work if some provide it and some don't?
Anyway we probably want some default implementations here? :) Like this and delegate as
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So
TableViewControlleractually sets this to the givenIndexPathso all implementers have to do is provide the property. Not sure if that makes sense to you? It just means all information is stored on the cell itself, and we don't need to fetch different bits of info from different places. Maybe I need to make that clearer in the docs?There was a problem hiding this comment.
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Well Apple choose not to put an
IndexPathproperty on theUITableViewCell. That's where the manager would hold onto that mapping. I'll come back to