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jessesquiresjessesquires
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fix formatting
1 parent 4d53537 commit 7effd57

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‎Sources/DiffableDataSource.swift

+87-86
Original file line numberDiff line numberDiff line change
@@ -40,113 +40,114 @@ extension DiffableDataSource {
4040
from source: CollectionViewModel,
4141
to destination: CollectionViewModel,
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animated: Bool,
43-
completion: SnapshotCompletion?) {
44-
// Build initial destination snapshot, then make adjustments below.
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var destinationSnapshot = DiffableSnapshot(viewModel: destination)
46-
47-
// Apply item reloads, then section reloads.
48-
// Reloading a section is required to properly reload headers, footers, and other supplementary views.
49-
// This 2-step process is necessary to preserve collection view animations
50-
// and prevent UIKit data source internal inconsistency exceptions.
51-
//
52-
// If we only reloaded a section (instead of reloading items first),
53-
// there are 2 problems:
54-
// 1. item updates would not animate correctly, because the whole section is reloaded.
55-
// 2. item inserts/deletes could trigger an internal inconsistency exception.
56-
57-
// Find and perform item (cell) updates first.
58-
let allSourceCells = source.allCellsByIdentifier
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let allDestinationCells = destination.allCellsByIdentifier
60-
var itemsToReload = [UniqueIdentifier]()
61-
62-
for (cellId, destinationCell) in allDestinationCells {
63-
let sourceCell = allSourceCells[cellId]
64-
65-
// If this cell exist in the source, and it has changed, then reload it.
66-
if destinationCell != sourceCell {
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itemsToReload.append(cellId)
68-
}
43+
completion: SnapshotCompletion?
44+
) {
45+
// Build initial destination snapshot, then make adjustments below.
46+
var destinationSnapshot = DiffableSnapshot(viewModel: destination)
47+
48+
// Apply item reloads, then section reloads.
49+
// Reloading a section is required to properly reload headers, footers, and other supplementary views.
50+
// This 2-step process is necessary to preserve collection view animations
51+
// and prevent UIKit data source internal inconsistency exceptions.
52+
//
53+
// If we only reloaded a section (instead of reloading items first),
54+
// there are 2 problems:
55+
// 1. item updates would not animate correctly, because the whole section is reloaded.
56+
// 2. item inserts/deletes could trigger an internal inconsistency exception.
57+
58+
// Find and perform item (cell) updates first.
59+
let allSourceCells = source.allCellsByIdentifier
60+
let allDestinationCells = destination.allCellsByIdentifier
61+
var itemsToReload = [UniqueIdentifier]()
62+
63+
for (cellId, destinationCell) in allDestinationCells {
64+
let sourceCell = allSourceCells[cellId]
65+
66+
// If this cell exist in the source, and it has changed, then reload it.
67+
if destinationCell != sourceCell {
68+
itemsToReload.append(cellId)
6969
}
70+
}
7071

71-
destinationSnapshot.reconfigureItems(itemsToReload)
72+
destinationSnapshot.reconfigureItems(itemsToReload)
7273

73-
// Apply snapshot with item reload updates.
74-
self.applySnapshot(destinationSnapshot, animated: animated) {
75-
// Once item reloads are complete, find and apply section reloads, if needed.
76-
// This is necessary to update SUPPLEMENTARY VIEWS ONLY.
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// Supplementary views do not get reloaded / reconfigured automatically when they change.
78-
// To trigger updates on supplementary views, the section must be reloaded.
79-
// Yes, this kinda sucks.
74+
// Apply snapshot with item reload updates.
75+
self.applySnapshot(destinationSnapshot, animated: animated) {
76+
// Once item reloads are complete, find and apply section reloads, if needed.
77+
// This is necessary to update SUPPLEMENTARY VIEWS ONLY.
78+
// Supplementary views do not get reloaded / reconfigured automatically when they change.
79+
// To trigger updates on supplementary views, the section must be reloaded.
80+
// Yes, this kinda sucks.
8081

81-
let allSourceSections = source.allSectionsByIdentifier
82+
let allSourceSections = source.allSectionsByIdentifier
8283

83-
// Only get sections that have supplementary views.
84-
let allDestinationSections = destination.allSectionsByIdentifier.filter { _, value in
85-
value.hasSupplementaryViews
84+
// Only get sections that have supplementary views.
85+
let allDestinationSections = destination.allSectionsByIdentifier.filter { _, value in
86+
value.hasSupplementaryViews
87+
}
88+
89+
// If no sections have supplementary views, there's nothing to do.
90+
guard allDestinationSections.isNotEmpty else {
91+
completion?()
92+
return
93+
}
94+
95+
var sectionsToReload = Set<UniqueIdentifier>()
96+
97+
// As soon as we find 1 supplementary view in a section that needs reloading,
98+
// we can mark the whole section for reload and exit early.
99+
for (sectionId, destinationSection) in allDestinationSections {
100+
// If this section does not exist in the source, then it is newly inserted.
101+
// Thus, nothing to do.
102+
guard let sourceSection = allSourceSections[sectionId] else {
103+
continue
86104
}
87105

88-
// If no sections have supplementary views, there's nothing to do.
89-
guard allDestinationSections.isNotEmpty else {
90-
completion?()
91-
return
106+
// If this section exist in the source,
107+
// and it has changed its SUPPLEMENTARY VIEWS ONLY,
108+
// then only reload the section.
109+
// First, check headers and footers.
110+
if destinationSection.header != sourceSection.header {
111+
sectionsToReload.insert(sectionId)
112+
continue
92113
}
93114

94-
var sectionsToReload = Set<UniqueIdentifier>()
115+
if destinationSection.footer != sourceSection.footer {
116+
sectionsToReload.insert(sectionId)
117+
continue
118+
}
95119

96-
// As soon as we find 1 supplementary view in a section that needs reloading,
97-
// we can mark the whole section for reload and exit early.
98-
for (sectionId, destinationSection) in allDestinationSections {
99-
// If this section does not exist in the source, then it is newly inserted.
100-
// Thus, nothing to do.
101-
guard let sourceSection = allSourceSections[sectionId] else {
102-
continue
103-
}
120+
// Next, check all supplementary views.
121+
let allSourceSectionSupplementaryViews = sourceSection.allSupplementaryViewsByIdentifier
104122

105-
// If this section exist in the source,
106-
// and it has changed its SUPPLEMENTARY VIEWS ONLY,
107-
// then only reload the section.
108-
// First, check headers and footers.
109-
if destinationSection.header != sourceSection.header {
110-
sectionsToReload.insert(sectionId)
123+
for destinationView in destinationSection.supplementaryViews {
124+
// If this view does not exist in the source, then it is newly added.
125+
// Thus, nothing to do.
126+
guard let sourceView = allSourceSectionSupplementaryViews[destinationView.id] else {
111127
continue
112128
}
113129

114-
if destinationSection.footer != sourceSection.footer {
130+
// After finding one view that needs reloading, we can stop,
131+
// because we have to reload the whole section anyway.
132+
if destinationView != sourceView {
115133
sectionsToReload.insert(sectionId)
116-
continue
117-
}
118-
119-
// Next, check all supplementary views.
120-
let allSourceSectionSupplementaryViews = sourceSection.allSupplementaryViewsByIdentifier
121-
122-
for destinationView in destinationSection.supplementaryViews {
123-
// If this view does not exist in the source, then it is newly added.
124-
// Thus, nothing to do.
125-
guard let sourceView = allSourceSectionSupplementaryViews[destinationView.id] else {
126-
continue
127-
}
128-
129-
// After finding one view that needs reloading, we can stop,
130-
// because we have to reload the whole section anyway.
131-
if destinationView != sourceView {
132-
sectionsToReload.insert(sectionId)
133-
break
134-
}
134+
break
135135
}
136136
}
137+
}
137138

138-
// If no section changes, ignore and call completion
139-
guard sectionsToReload.isNotEmpty else {
140-
completion?()
141-
return
142-
}
139+
// If no section changes, ignore and call completion
140+
guard sectionsToReload.isNotEmpty else {
141+
completion?()
142+
return
143+
}
143144

144-
destinationSnapshot.reloadSections(sectionsToReload.toArray)
145+
destinationSnapshot.reloadSections(sectionsToReload.toArray)
145146

146-
// Apply final section updates
147-
self.applySnapshot(destinationSnapshot, animated: animated, completion: completion)
148-
}
147+
// Apply final section updates
148+
self.applySnapshot(destinationSnapshot, animated: animated, completion: completion)
149149
}
150+
}
150151

151152
func applySnapshot(_ snapshot: Snapshot, animated: Bool, completion: SnapshotCompletion? = nil) {
152153
self.apply(snapshot, animatingDifferences: animated, completion: completion)

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