如何解决当我用鼠标单击更改 SwiftUI 列表的选择时,@Published 属性的 didSet 被调用两次
我将 SwiftUI 用于我的 Mac OS 应用程序。当我通过鼠标单击 didSet 在 SidebarView 中更改 List 的选择(从 收件箱 到 今天)时 被调用两次(侧边栏正文也被计算两次)。如果我用箭头(向下 | 向上)更改选择,didSet 将被调用一次。是bug吗?我为我的英语感到抱歉。
日志:
- 点击鼠标:
willSet = Optional(MiniTodo.NavigationItem.inBox) 2021-04-18 00:36:20 +0000
didSet = Optional(MiniTodo.NavigationItem.inBox) 2021-04-18 00:36:20 +0000
willSet = Optional(MiniTodo.NavigationItem.inBox) 2021-04-18 00:36:20 +0000
didSet = Optional(MiniTodo.NavigationItem.today) 2021-04-18 00:36:20 +0000
- 带箭头:
willSet = Optional(MiniTodo.NavigationItem.inBox) 2021-04-18 00:37:11 +0000
didSet = Optional(MiniTodo.NavigationItem.today) 2021-04-18 00:37:11 +0000
import SwiftUI
class UIState: ObservableObject {
@Published var navigationItem: NavigationItem? = .inBox {
didSet {
print("didSet = \(navigationItem) \(Date())")
}
willSet {
print("willSet = \(navigationItem) \(Date())")
}
}
}
struct MiniTodoApp: App {
let persistenceController = PersistenceController.shared
@StateObject var uiState: UIState = UIState()
var body: some Scene {
WindowGroup {
NavigationView {
SidebarView()
.environmentObject(uiState)
//ContentView()
}
.navigationViewStyle(DoubleColumnNavigationViewStyle())
.environment(\.managedobjectContext,persistenceController.container.viewContext)
}
}
}
struct SidebarView: View {
@Environment(\.managedobjectContext) private var viewContext
@EnvironmentObject var uiState: UIState
@FetchRequest(
sortDescriptors: [NSSortDescriptor(keyPath: \Folder.name,ascending: true)],animation: .default)
private var folders: FetchedResults<Folder>
var body: some View {
print("==== Sidebar View ====")
print(#function)
print("======================")
print("")
return List(selection: $uiState.navigationItem) {
Group {
Label("InBox",systemImage: "tray")
.tag(NavigationItem.inBox)
Label("Today",systemImage: "sun.max.fill")
.listItemTint(.yellow)
.tag(NavigationItem.today)
Label("Plan",systemImage: "calendar")
.listItemTint(.red)
.tag(NavigationItem.plan)
Label("Completed",systemImage: "checkmark.square.fill")
.listItemTint(.green)
.tag(NavigationItem.completed)
}
Section(header:
HStack {
Text("Lists")
Spacer()
//if self.onHover {
Button {
withAnimation {
newFolder()
}
} label: {
Image(systemName: "plus.circle")
}
.buttonStyle(BorderlessButtonStyle())
.padding(EdgeInsets(top: 0.0,leading: 0.0,bottom: 0.0,trailing: 10.0))
// }
}
) {
ForEach(folders) { folder in
FolderRow(folder: folder)
.tag(NavigationItem.folder(folder: folder))
}
} // Section
.collapsible(false)
} // List
.listStyle(SidebarListStyle())
.toolbar {
ToolbarItem(placement: .navigation){
Button(action: toggleSidebar,label: {
Image(systemName: "sidebar.left")
})
}
}
} // body
// Toggle Sidebar Function
func toggleSidebar() {
NSApp.keyWindow?.firstResponder?.tryToPerform(#selector(NssplitViewController.toggleSidebar(_:)),with: nil)
}
func newFolder() {
withAnimation {
let newItem = Folder(context: viewContext)
newItem.name = "It is new folder"
do {
try viewContext.save()
} catch {
// Replace this implementation with code to handle the error appropriately.
// fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application,although it may be useful during development.
let nsError = error as NSError
fatalError("Unresolved error \(nsError),\(nsError.userInfo)")
}
}
}
}
解决方法
您可以在 navigationItem 发布者之上使用 debounce
函数,并且您只会收到一次 didSet
:
class UIState: ObservableObject {
@Published var navigationItem: NavigationItem? = .inbox
var cancellable: AnyCancellable?
init() {
self.cancellable = $navigationItem.debounce(
for: .microseconds(1),scheduler: RunLoop.main
).sink { _ in
print("DID SET")
// Do Whatever you want
}
}
}
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