In my app which uses SwiftUI for interface I have a button that performs an action:
func getBooksCountNumber() -> Int {
var countResult = 0
let booksFetch = NSFetchRequest<NSFetchRequestResult>(entityName: "Book")
do {
let booksFetch = try self.persistentContainer.viewContext.fetch(booksFetch) as! [Book]
countResult = booksFetch.count
print("countResult is \(countResult)")
} catch {
fatalError("Failed to fetch: \(error)")
}
return countResult
}
When I delete rows in the app I use moc.delete(book) and try? moc.save(). I see that deleted rows gone, using interface at icloud.developer.apple.com. For example — if from 3 records I delete 1, I still getting 3 in countResult and not 2. Any help is appreciated.
SwiftUI relies on data invalidation to force a View to reload.
So you need to think about how you make your View code rely on the change in your data, for countResult (as an example).
If you're using SwiftUI, I'd recommend that you consider using the #FetchRequest property wrapper to acquire your dataset...
#FetchRequest(entity: Book.entity(),
sortDescriptors: []
) var books: FetchedResults<Book>
Note: the sortDescriptors: parameter is required, so if you do not want to sort the FetchedResults, you include an empty array [].
Then use the property associated with that wrapper to feed the data into your view...
struct YourView: View {
// #FetchRequest here
var body: some View {
...
Text("Book count = \(books.count)")
...
}
}
This way, you don't even need to press the button to determine the count, because the Text view is updated each time a book is added to or deleted from your Book entity.
Written in a SwiftUI way, as the data changes, the Text view component will be invalidated and the view struct will be forced to redraw.
If you want to keep the button in your view, you could do something like this instead...
var body: some View {
...
Button(action: {
// code to perform your action here...
}) {
Text("You have \(books.count) books")
}
...
}
Where the label of the button includes the count of books (and the button performs some other action).
Related
Sorry to make this post so long, but in hindsight I should have shown you the simpler instance of the issue so you could better understand what the problem is. I am assuming the same issue with ForEach is at the root cause of both of these bugs, but I could be wrong. The second instance is still included to give you context, but the first intance should be all you need to fully understand the issue.
First Instance:
Here is a video of the issue: https://imgur.com/a/EIg9TSm. As you can see, there are 4 Time Codes, 2 of which are favorite and 2 are not favorites (shown by the yellow star). Additionally, there is text at the top that represents the array of Time Codes being displayed just as a list of favorite (F) or not favorite (N). I click on the last Time Code (Changing to favorite) and press the toggle to unfavorite it. When I hit save, the array of Time Codes is updated, yet as you see, this is not represented in the List. However, you see that the Text of the reduced array immediately updates to FNFF, showing that it is properly updated as a favorite by the ObservedObject.
When I click back on the navigation and back to the page, the UI is properly updated and there are 3 yellow stars. This makes me assume that the problem is with ForEach, as the Text() shows the array is updated but the ForEach does not. Presumably, clicking out of the page reloads the ForEach, which is why it updates after exiting the page. EditCodeView() handles the saving of the TimeCodeVieModel in CoreData, and I am 99% certain that it works properly through my own testing and the fact that the ObservedObject updates as expected. I am pretty sure I am using the dynamic version of ForEach (since TimeCodeViewModel is Identifiable), so I don't know how to make the behavior update immediately after saving. Any help would be appreciated.
Here is the code for the view:
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)
}
}
}
}
}
}
Here is the code for the View Models (shouldn't be relevant to the problem, but included for understanding):
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!
}
}
Second Instance:
EDIT: I realize it may be difficult to understand what the code is doing, so I have included a gif demoing the problem (unfortunately I am not high enough reputation for it to be shown automatically). As you can see, I select the cells I want to change, then press the button to assign that TimeCode to it. The array of TimeCodeCellViewModels changes in the background, but you don't actually see that change until I press the home button and then reopen the app, which triggers a refresh of ForEach. Gif of issue. There is also this video if the GIF is too fast: https://imgur.com/a/Y5xtLJ3
I am trying to display a grid view using a VStack of HStacks, and am running into an issue where the ForEach I am using to display the content is not refreshing when the array being passed in changes. I know the array itself is changing because if I reduce it to a string and display the contents with Text(), it properly updates as soon as a change is made. But, the ForEach loop only updates if I close and reopen the app, forcing the ForEach to reload. I know that there is a special version of ForEach that is specifically designed for dynamic content, but I am pretty sure I am using this version since I pass in '''id: .self'''. Here is the main code snippet:
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)
}
}
}
}
I'm pretty sure it doesn't change anything, but I did have to define a custom hash function for the TimeCodeCellViewModel, which might change the behavior of the ForEach (the attributes being changed are included in the hash function). However, I have noticed the same ForEach behavior in another part of my project that uses a different view model, so I highly doubt this is the issue.
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!
}
}
Here is a snippet of what you need to make the code work.
See the comments for some basics of why
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
}
}
Your first ForEach probably cannot check if the identity of Array<TimeCodeCellViewModel> has changed.
Perhaps you want to use a separate struct which holds internally an array of TimeCodeCellViewModel and conforms to Identifiable, effectively implementing such protocol.
stuct TCCViewModels: Identifiable {
let models: Array<TimeCodeCellViewModel>
var id: Int {
models.hashValue
}
}
You might as well make this generic too, so it can be reused for different view models in your app:
struct ViewModelsContainer<V: Identifiable> where V.ID: Hashable {
let viewModels: Array<V>
let id: Int
init(viewModels: Array<V>) {
self.viewModels = viewModels
var hasher = Hasher()
hasher.combine(viewModels.count)
viewModels.forEach { hasher.combine($0.id) }
self.id = hasher.finalize
}
}
I have a data model in my SwiftUI app that looks something like this:
struct Entry: Identifiable{
var id = UUID().uuidString
var name = ""
var duration: Int{
//An SQLite query that returns the total of the "duration" column
let total = try! dbc.scalar(tableFlight.filter(db.entry == id).select(db.duration.total))
return Int(total)
}
}
struct Flight: Identifiable{
var id = UUID().uuidString
var duration = 0
var entry: String?
}
I have an ObservableObject view model that produces the entries like this:
class EntryModel: ObservableObject{
static let shared = EntryModel()
#Published var entries = [Entry]()
init(){
get()
}
func get(){
//Stuff to fetch the entries
entries = //SQLite query that returns an array of Entry objects
}
}
Then finally, in my View, I list all the entry names and their associated duration like this:
ForEach(modelEntry.entries){ entry in
VStack{
Text(entry.name) //<-- Updates fine
Text(entry.duration) //<-- Gets set initially, but no updates
}
}
The issue I'm having is that when I update a Flight for that Entry, the duration in my view doesn't update. I know that won't happen because only the entries will redraw when they are changed.
But even if I manually call the get() function in my EntryModel, the associated duration still doesn't update.
Is there a better way to do this? How do I get the parent's computed properties to recalculate when its child element is updated?
I figured it out. My actual code used a child View inside the ForEach where the VStack is. I was just passing an entry to it, so the values were only getting set initially and were thus not reactive.
By changing that entry to a Binding, it's working:
ForEach($modelEntry.entries){ $entry in
ChildView(entry: $entry)
}
Note that the $ on the $modelEntry and the return $entry is an Xcode 13+ feature (but backward compatible to iOS 14 and macOS 11.0).
I'm working on an app that needs to open on the users last used view even if the app is completly killed by the user or ios.
As a result I'm holding last view used in UserDefaults and automatically moving the user through each view in the stack until they reach their destination.
The code on each view is as follows:
#Binding var redirectionID: Int
VStack() {
List {
NavigationLink(destination: testView(data: data, moc: moc), tag: data.id, selection:
$redirectionId) {
DataRow(data: data)
}
}
}.onAppear() {
redirectionID = userData.lastActiveView
}
Is there a better / standard way to achieve this? This works reasonably on iOS 14.* but doesn't work very well on iOS 13.* On iOS 13.* The redirection regularly doesnt reach its destination page and non of the preceeding views in the stack seem to be created. Pressing back etc results in a crash.
Any help / advice would be greatly appreciated.
This sounds like the perfect use of if SceneStorage
"You use SceneStorage when you need automatic state restoration of the value. SceneStorage works very similar to State, except its initial value is restored by the system if it was previously saved, and the value is· shared with other SceneStorage variables in the same scene."
#SceneStorage("ContentView.selectedProduct") private var selectedProduct: String?
#SceneStorage("DetailView.selectedTab") private var selectedTab = Tabs.detail
It is only available in iOS 14+ though so something manual would have to be implemented. Maybe something in CoreData. An object that would have variables for each important state variable. It would work like an ObservedObject ViewModel with persistence.
Also. you can try...
"An NSUserActivity object captures the app’s state at the current moment in time. For example, include information about the data the app is currently displaying. The system saves the provided object and returns it to the app the next time it launches. The sample creates a new NSUserActivity object when the user closes the app or the app enters the background."
Here is some sample code that summarizes how to bring it all together. It isn't a minimum reproducible example because it is a part of the larger project called "Restoring Your App's State with SwiftUI" from Apple. But it gives a pretty good picture on how to implement it.
struct ContentView: View {
// The data model for storing all the products.
#EnvironmentObject var productsModel: ProductsModel
// Used for detecting when this scene is backgrounded and isn't currently visible.
#Environment(\.scenePhase) private var scenePhase
// The currently selected product, if any.
#SceneStorage("ContentView.selectedProduct") private var selectedProduct: String?
let columns = Array(repeating: GridItem(.adaptive(minimum: 94, maximum: 120)), count: 3)
var body: some View {
NavigationView {
ScrollView {
LazyVGrid(columns: columns) {
ForEach(productsModel.products) { product in
NavigationLink(destination: DetailView(product: product, selectedProductID: $selectedProduct),
tag: product.id.uuidString,
selection: $selectedProduct) {
StackItemView(itemName: product.name, imageName: product.imageName)
}
.padding(8)
.buttonStyle(PlainButtonStyle())
.onDrag {
/** Register the product user activity as part of the drag provider which
will create a new scene when dropped to the left or right of the iPad screen.
*/
let userActivity = NSUserActivity(activityType: DetailView.productUserActivityType)
let localizedString = NSLocalizedString("DroppedProductTitle", comment: "Activity title with product name")
userActivity.title = String(format: localizedString, product.name)
userActivity.targetContentIdentifier = product.id.uuidString
try? userActivity.setTypedPayload(product)
return NSItemProvider(object: userActivity)
}
}
}
.padding()
}
.navigationTitle("ProductsTitle")
}
.navigationViewStyle(StackNavigationViewStyle())
.onContinueUserActivity(DetailView.productUserActivityType) { userActivity in
if let product = try? userActivity.typedPayload(Product.self) {
selectedProduct = product.id.uuidString
}
}
.onChange(of: scenePhase) { newScenePhase in
if newScenePhase == .background {
// Make sure to save any unsaved changes to the products model.
productsModel.save()
}
}
}
}
In my SwiftUI code, I create a view called LineView() (this is from the graph library for swift on github here). I am trying to generate data from it using the function firestoreManager().getUserData(). There are many moving pieces in this piece of code and I will try to explain them. The User datatype is a user, the userInfo.updateStockChart()gives the updated data. However, that isn't important. What is important is that the code in the firestoreManager.getUserData() closure runs after the LineView() creation code (note that the closure code uses the google swift promise library to run). I need that code to run BEFORE the LineView(). Any Ideas?
I have tried to solve this many ways, but since the VStack is strongly tied to the struct, I am not sure how.
struct homepageView: View {
#State var data: [Double] = [0,1,2]
var body: some View {
var userInfo: User = User(username: "", name: "", portfolioID: "", friendList: [])
var theData: [Double] = self.data
firestoreManager().getUserData(collection: "Users", documentVar: "darrow_h19", documentField: "Username").then{ user in
userInfo = user
theData = userInfo.updateStockChart(portfolioID: "123456")
print(theData)
}
print(theData)
return VStack {
LineView(data: theData, title: "$XYZ", legend: "Hello World",totalPoints: 18,yPosChange: 300)
}
}
}
I have a class, a “clock face” with regular updates; it should display an array of metrics that change over time.
Because I’d like the clock to also be displayed in a widget, I’ve found that I had to put the class into a framework (perhaps there’s another way, but I’m too far down the road now). This appears to have caused a problem with SwiftUI and observable objects.
In my View I have:
#ObservedObject var clockFace: myClock
In the clock face I have:
class myClock: ObservableObject, Identifiable {
var id: Int
#Publish public var metric:[metricObject] = []
....
// at some point the array is mutated and the display updates
}
I don’t know if Identifiable is needed but it’s doesn’t make any difference to the outcome. The public is demanded by the compiler, but it’s always been like that anyway.
With these lines I get a runtime error as the app starts:
objc[31175] no class for metaclass
So I took off the #Published and changed to a manual update:
public var metric:[metricObject] = [] {
didSet {
self.objectWillChange.send()`
}
}
And now I get a display and by setting a breakpoint I can see the send() is being called at regular intervals. But the display won’t update unless I add/remove from the array. I’m guessing the computed variables (which make up the bulk of the metricObject change isn’t being seen by SwiftUI. I’ve subsequently tried adding a “dummy” Int to the myClock class and setting that to a random value to trying to trigger a manual refresh via a send() on it’s didSet with no luck.
So how can I force a periodic redraw of the display?
What is MetricObject and can you make it a struct so you get Equatable for free?
When I do this with an Int it works:
class PeriodicUpdater: ObservableObject {
#Published var time = 0
var subscriptions = Set<AnyCancellable>()
init() {
Timer
.publish(every: 1, on: .main, in: .default)
.autoconnect()
.sink(receiveValue: { _ in
self.time = self.time + 1
})
.store(in: &subscriptions)
}
}
struct ContentView: View {
#ObservedObject var updater = PeriodicUpdater()
var body: some View {
Text("\(self.updater.time)")
}
}
So it's taken a while but I've finally got it working. The problem seemed to be two-fold.
I had a class defined in my framework which controls the SwiftUI file. This class is sub-classed in both the main app and the widget.
Firstly I couldn't use #Published in the main class within the framework. That seemed to cause the error:
objc[31175] no class for metaclass
So I used #JoshHomman's idea of an iVar that's periodically updated but that didn't quite work for me. With my SwiftUI file, I had:
struct FRMWRKShape: Shape {
func drawShape(in rect: CGRect) -> Path {
// draw and return a shape
}
}
struct ContentView: View {
#ObservedObject var updater = PeriodicUpdater()
var body: some View {
FRMWRKShape()
//....
FRMWRKShape() //slightly different parameters are passed in
}
}
The ContentView was executed every second as I wanted, however the FRMWRKShape code was called but not executed(?!) - except on first starting up - so the view doesn't update. When I changed to something far less D.R.Y. such as:
struct ContentView: View {
#ObservedObject var updater = PeriodicUpdater()
var body: some View {
Path { path in
// same code as was in FRMWRKShape()
}
//....
Path { path in
// same code as was in FRMWRKShape()
// but slightly different parameters
}
}
}
Magically, the View was updated as I wanted it to be. I don't know if this is expected behaviour, perhaps someone can say whether I should file a Radar....