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Serialize access to the UITableView for scrolling and diffable datasource updates. Issue #1806

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This commit is contained in:
Maurice Parker
2020-02-23 10:57:20 -08:00
parent fd0363aad2
commit 48e856fc04
6 changed files with 119 additions and 45 deletions
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56
iOS/MasterFeed/MasterFeedViewController.swift
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@@ -17,8 +17,10 @@ class MasterFeedViewController: UITableViewController, UndoableCommandRunner {
@IBOutlet weak var filterButton: UIBarButtonItem!
private var refreshProgressView: RefreshProgressView?
@IBOutlet weak var addNewItemButton: UIBarButtonItem!
private let operationQueue = MainThreadOperationQueue()
lazy var dataSource = makeDataSource()
var undoableCommands = [UndoableCommand]()
weak var coordinator: SceneCoordinator!
@@ -27,7 +29,6 @@ class MasterFeedViewController: UITableViewController, UndoableCommandRunner {
return keyboardManager.keyCommands
}
var restoreSelection = false
override var canBecomeFirstResponder: Bool {
return true
}
@@ -73,17 +74,6 @@ class MasterFeedViewController: UITableViewController, UndoableCommandRunner {
updateUI()
super.viewWillAppear(animated)
}
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
// We have to delay the selection of the Feed until the subviews have been layed out
// so that the visible area is correct and we scroll correctly.
if restoreSelection {
restoreSelectionIfNecessary(adjustScroll: true)
restoreSelection = false
}
}
// MARK: Notifications
@@ -144,10 +134,6 @@ class MasterFeedViewController: UITableViewController, UndoableCommandRunner {
}
}
@objc func webFeedMetadataDidChange(_ note: Notification) {
reloadAllVisibleCells()
}
@objc func contentSizeCategoryDidChange(_ note: Notification) {
resetEstimatedRowHeight()
applyChanges(animated: false)
@@ -517,24 +503,7 @@ class MasterFeedViewController: UITableViewController, UndoableCommandRunner {
}
func updateFeedSelection(animations: Animations) {
if dataSource.snapshot().numberOfItems > 0 {
if let indexPath = coordinator.currentFeedIndexPath {
if tableView.indexPathForSelectedRow != indexPath {
tableView.selectRowAndScrollIfNotVisible(at: indexPath, animations: animations)
}
} else {
if animations.contains(.select) {
// This nasty bit of duct tape is because there is something, somewhere
// interrupting the deselection animation, which will leave the row selected.
// This seems to get it far enough away the problem that it always works.
DispatchQueue.main.async {
self.tableView.selectRow(at: nil, animated: true, scrollPosition: .none)
}
} else {
self.tableView.selectRow(at: nil, animated: false, scrollPosition: .none)
}
}
}
operationQueue.add(UpdateSelectionOperation(coordinator: coordinator, dataSource: dataSource, tableView: tableView, animations: animations))
}
func reloadFeeds(initialLoad: Bool, completion: (() -> Void)? = nil) {
@@ -646,7 +615,7 @@ private extension MasterFeedViewController {
func reloadNode(_ node: Node) {
var snapshot = dataSource.snapshot()
snapshot.reloadItems([node])
dataSource.apply(snapshot, animatingDifferences: false) { [weak self] in
queueApply(snapshot: snapshot, animatingDifferences: false) { [weak self] in
self?.restoreSelectionIfNecessary(adjustScroll: false)
}
}
@@ -661,13 +630,22 @@ private extension MasterFeedViewController {
snapshot.appendItems(shadowTableNodes, toSection: sectionNode)
}
dataSource.apply(snapshot, animatingDifferences: animated) { [weak self] in
queueApply(snapshot: snapshot, animatingDifferences: animated) { [weak self] in
self?.restoreSelectionIfNecessary(adjustScroll: adjustScroll)
completion?()
}
}
func queueApply(snapshot: NSDiffableDataSourceSnapshot<Node, Node>, animatingDifferences: Bool = true, completion: (() -> Void)? = nil) {
let operation = MasterFeedDataSourceOperation(dataSource: dataSource, snapshot: snapshot, animating: animatingDifferences)
operation.completionBlock = { _ in
completion?()
}
operationQueue.add(operation)
}
func makeDataSource() -> UITableViewDiffableDataSource<Node, Node> {
func makeDataSource() -> MasterFeedDataSource {
let dataSource = MasterFeedDataSource(tableView: tableView, cellProvider: { [weak self] tableView, indexPath, node in
let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) as! MasterFeedTableViewCell
self?.configure(cell, node)
@@ -774,7 +752,7 @@ private extension MasterFeedViewController {
private func reloadCells(_ nodes: [Node], completion: (() -> Void)? = nil) {
var snapshot = dataSource.snapshot()
snapshot.reloadItems(nodes)
dataSource.apply(snapshot, animatingDifferences: false) { [weak self] in
queueApply(snapshot: snapshot, animatingDifferences: false) { [weak self] in
self?.restoreSelectionIfNecessary(adjustScroll: false)
completion?()
}