ForEach未使用动态内容SwiftUI正确更新 [英] ForEach not properly updating with dynamic content SwiftUI
本文介绍了ForEach未使用动态内容SwiftUI正确更新的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
第一个实例：
这是这个问题的视频：https://imgur.com/a/EIg9TSm。如您所见，有4个时间代码，其中2个是最喜欢的，2个不是最喜欢的(用黄色星号表示)。此外，顶部有表示时间代码数组的文本，仅显示为收藏(F)或不收藏(N)列表。我点击Last Time Code(更改为收藏)，然后按切换以取消收藏。当我点击保存时，时间代码数组被更新，但是正如您所看到的，列表中没有显示时间代码。但是，您会看到缩减数组的文本立即更新为FNFF，表明它已正确更新为ObservedObject的收藏夹。
当我单击导航并返回页面时，UI已正确更新，并且有3颗黄色星号。这让我假设问题出在ForEach上，因为文本()显示数组已更新，但ForEach没有。在页面外单击可能会重新加载ForEach，这就是它在退出页面后更新的原因。EditCodeView()处理CoreData中TimeCodeVieModel的保存，通过我自己的测试和ObservedObject按预期更新的事实，我99%确定它工作正常。我非常确定我使用的是ForEach的动态版本(因为TimeCodeViewModel是可识别的)，所以我不知道如何在保存后立即更新行为。如有任何帮助，我们将不胜感激。
以下是视图的代码：
struct ListTimeCodeView: View {
@ObservedObject var timeCodeListVM: TimeCodeListViewModel
@State var presentEditTimeCode: Bool = false
@State var timeCodeEdit: TimeCodeViewModel?
init() {
self.timeCodeListVM = TimeCodeListViewModel()
}
var body: some View {
VStack {
HStack {
Text("TimeCodes Reduced by Favorite:")
Text("(self.timeCodeListVM.timeCodes.reduce(into: "") {$0 += $1.isFavorite ? "F" : "N"})")
}
List {
ForEach(self.timeCodeListVM.timeCodes) { timeCode in
TimeCodeDetailsCell(fullName: timeCode.fullName, abbreviation: timeCode.abbreviation, color: timeCode.color, isFavorite: timeCode.isFavorite, presentEditTimeCode: $presentEditTimeCode)
.contentShape(Rectangle())
.onTapGesture {
timeCodeEdit = timeCode
}
.sheet(item: $timeCodeEdit, onDismiss: didDismiss) { detail in
EditCodeView(timeCodeEdit: detail)
}
}
}
}
}
}
以下是视图模型的代码(不应该与问题相关，但包含在其中是为了理解)：
class TimeCodeListViewModel: ObservableObject {
@Published var timeCodes = [TimeCodeViewModel]()
init() {
fetchAllTimeCodes()
}
func fetchAllTimeCodes() {
self.timeCodes = CoreDataManager.shared.getAllTimeCodes().map(TimeCodeViewModel.init)
}
}
class TimeCodeViewModel: Identifiable {
var id: String = ""
var fullName = ""
var abbreviation = ""
var color = ""
var isFavorite = false
var tags = ""
init(timeCode: TimeCode) {
self.id = timeCode.id!.uuidString
self.fullName = timeCode.fullName!
self.abbreviation = timeCode.abbreviation!
self.color = timeCode.color!
self.isFavorite = timeCode.isFavorite
self.tags = timeCode.tags!
}
}
第二个实例：
编辑：我意识到可能很难理解代码在做什么，所以我包含了一个演示问题的gif(不幸的是，我的声誉还不够高，无法让它自动显示)。如您所见，我选择了要更改的单元格，然后按下按钮将时间码分配给它。TimeCodeCellViewModels数组在后台发生变化，但在我按下主页按钮并重新打开应用程序(这会触发ForEach刷新)之前，您实际上看不到这种变化。Gif of issue。如果GIF太快，还有这个视频：https://imgur.com/a/Y5xtLJ3
我试图使用HStacks的VStack显示网格视图，但遇到了一个问题，当传入的数组更改时，我用来显示内容的ForEach没有刷新。我知道数组本身正在更改，因为如果我将其简化为字符串并使用text()显示内容，则一旦进行更改，它就会立即正确更新。但是，ForEach循环只有在我关闭并重新打开应用程序时才会更新，从而强制ForEach重新加载。我知道ForEach有一个专门为动态内容设计的特殊版本，但我非常确定我正在使用这个版本，因为我传入了""id：.self""。以下是主要代码片段：
var hoursTimeCode: [[TimeCodeCellViewModel]] = []
// initialize hoursTimeCode
VStack(spacing: 3) {
ForEach(self.hoursTimeCode, id: .self) {row in
HStack(spacing: 3){
HourTimeCodeCell(date: row[0].date) // cell view for hour
.frame(minWidth: 50)
ForEach(row.indices, id: .self) {cell in
// TimeCodeBlockCell displays minutes normally. If it is selected, and a button is pressed, it is assigned a TimeCode which it will then display
TimeCodeBlockCell(timeCodeCellVM: row[cell], selectedArray: $selectedTimeCodeCells)
.frame(maxWidth: .infinity)
.aspectRatio(1.0, contentMode: .fill)
}
}
}
}
我非常确定它不会改变任何事情，但是我必须为TimeCodeCellViewModel定义一个自定义散列函数，这可能会改变ForEach的行为(被改变的属性包含在散列函数中)。但是，我在使用不同视图模型的项目的另一部分中注意到了相同的ForEach行为，因此我非常怀疑这就是问题所在。
class TimeCodeCellViewModel:Identifiable, Hashable {
static func == (lhs: TimeCodeCellViewModel, rhs: TimeCodeCellViewModel) -> Bool {
if lhs.id == rhs.id {
return true
}
else {
return false
}
}
func hash(into hasher: inout Hasher) {
hasher.combine(id)
hasher.combine(isSet)
hasher.combine(timeCode)
hasher.combine(date)
}
var id: String = ""
var date = Date()
var isSet = false
var timeCode: TimeCode
var frame: CGRect = .zero
init(timeCodeCell: TimeCodeCell) {
self.id = timeCodeCell.id!.uuidString
self.date = timeCodeCell.date!
self.isSet = timeCodeCell.isSet
self.timeCode = timeCodeCell.toTimeCode!
}
}
推荐答案
下面是代码正常工作所需的代码片段。
有关原因的一些基本信息，请参阅备注
struct EditCodeView:View{
@EnvironmentObject var timeCodeListVM: TimeCodeListViewModel
//This will observe changes to the view model
@ObservedObject var timeCodeViewModel: TimeCodeViewModel
var body: some View{
EditTimeCodeView(timeCode: timeCodeViewModel.timeCode)
.onDisappear(perform: {
//*********TO SEE CHANGES WHEN YOU EDIT
//uncomment this line***********
//_ = timeCodeListVM.update(timeCodeVM: timeCodeViewModel)
})
}
}
struct EditTimeCodeView: View{
//This will observe changes to the core data entity
@ObservedObject var timeCode: TimeCode
var body: some View{
Form{
TextField("name", text: $timeCode.fullName.bound)
TextField("appreviation", text: $timeCode.abbreviation.bound)
Toggle("favorite", isOn: $timeCode.isFavorite)
}
}
}
class TimeCodeListViewModel: ObservableObject {
//Replacing this whole thing with a @FetchRequest would be way more efficient than these extra view models
//IF you dont want to use @FetchRequest the only other way to observe the persistent store for changes is with NSFetchedResultsController
//https://stackoverflow.com/questions/67526427/swift-fetchrequest-custom-sorting-function/67527134#67527134
//This array will not see changes to the variables of the ObservableObjects
@Published var timeCodeVMs = [TimeCodeViewModel]()
private var persistenceManager = TimeCodePersistenceManager()
init() {
fetchAllTimeCodes()
}
func fetchAllTimeCodes() {
//This method does not observe for new and or deleted timecodes. It is a one time thing
self.timeCodeVMs = persistenceManager.retrieveObjects(sortDescriptors: nil, predicate: nil).map({
//Pass the whole object there isnt a point to just passing the variables
//But the way you had it broke the connection
TimeCodeViewModel(timeCode: $0)
})
}
func addNew() -> TimeCodeViewModel{
let item = TimeCodeViewModel(timeCode: persistenceManager.addSample())
timeCodeVMs.append(item)
//will refresh view because there is a change in count
return item
}
///Call this to save changes
func update(timeCodeVM: TimeCodeViewModel) -> Bool{
let result = persistenceManager.updateObject(object: timeCodeVM.timeCode)
//You have to call this to see changes at the list level
objectWillChange.send()
return result
}
}
//DO you have special code that you aren't including? If not what is the point of this view model?
class TimeCodeViewModel: Identifiable, ObservableObject {
//Simplify this
//This is a CoreData object therefore an ObservableObject it needs an @ObservedObject in a View so changes can be seem
@Published var timeCode: TimeCode
init(timeCode: TimeCode) {
self.timeCode = timeCode
}
}
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