Fix tab content view recreation #24
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Hello, @winddpan, thank you for your PR!
I have reviewed your changes and highlighted some issues that need to be addressed before merging. Also, if I understand your approach correctly, you plan to introduce a StateObject entity to store the items of TabBar and the selection property. If this approach successfully resolves the issue with unexpected view recreation, we should consider removing the PreferenceKey usage, as it would become redundant.
| @State private var items: [TabItem] | ||
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| @StateObject private var selectedItem: TabBarSelection<TabItem> | ||
| private let content: () -> Content |
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Storing the closure as a parameter rather than invoking it immediately could lead to performance issues, as it disrupts the memoization process of SwiftUI.
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In fact, delayed closures perform better in practice. SwiftUI needs to construct View instances to compare function signatures, resulting in a higher frequency of View initialization compared to the View body getter.
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Storing closures in a parameter makes the View (in this case TabBar) to re-evaluate on every @State change of the on the closure provider side, even on unrelated one, because closures are not Equatable and SwiftUI cannot check if the return value of this closure changed or not.
| struct TextWrapper: View { | ||
| @State var string: String = UUID().uuidString | ||
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| var body: some View { | ||
| Text(string) | ||
| .onTapGesture { | ||
| string = UUID().uuidString | ||
| } | ||
| .onAppear(perform: { | ||
| print("onAppear:", string) | ||
| }) | ||
| } | ||
| } |
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Could you please clarify the purpose of this wrapper? I didn't quite understand it.
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Just for the purpose of testing recreation and lazy loading, no other meaning.
If you don't like it, I can minimize the PR.
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I think it will be better revert these changes, as Example project most likely will be updated later.
| .onChange(of: selection) { newValue in | ||
| print("selection changed:", newValue) | ||
| } |
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I think we should remove this print statement, as it doesn't add any significant value here.
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Just for the purpose of testing, can remove it.
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Updated the base branch to |
This PR intent to prevent tab content view recreation.
Mainly used StateObject to maintain the state and set opacity=0 to keep the view. (And aslo support tab content view lazy loading)
Sorry for the many format changes due to SwiftFormat. Also, I made some modifications to the test the view keeping in the demo. If you don't like it, I can submit a new PR with minimal changes.