I am dragging and dropping views using a DropDelegate in SwiftUI. I'm successfully wrapping my data in an NSItemProvider using the .onDrag View Modifier, and I even have .onDrop working if I am able to have my drop data be one of the stored properties of my DropDelegate.
I'm trying to allow for decoding my drop data using the provided DropInfo. I update my view in the dropEntered(info:) delegate method, so that the user can have a preview of their drop before it occurs. When I write
info.itemProviders.first?.loadObject(...) { reading, error in
...
}
The completion handler is not called. If I were to instead write this closure in the performDrop(info:) delegate method, the completion handler would be called. Why is the completion handler only called in performDrop(info:)? Is there a way to have drag & drop previews while performing the necessary changes in real time while not having the data model changed in dropEntered(info:)?
I don't love that I edit my data model in dropEntered(info:), and I haven't gotten to how it would work if the user were to cancel the drag and drop somehow... Perhaps there's a better way to go about this that will allow me to edit my data model in performDrop(info:)?
Thank you!
Edit
Here's the code to reproduce the bug:
struct ReorderableForEach<Content: View, Item: Identifiable>: View {
let items: [Item]
let content: (Item) -> Content
var body: some View {
ForEach(items) { item in
content(item)
.onDrag {
return NSItemProvider(object: "\(item.id)" as NSString)
}
.onDrop(
of: [.text],
delegate: DragRelocateDelegate()
)
}
}
}
struct DragRelocateDelegate: DropDelegate {
func dropEntered(info: DropInfo) {
let _ = info.itemProviders(for: [.text]).first?.loadObject(ofClass: String.self) { item, error in
print("dropEntered: \(item)") // Won't trigger this
}
}
func performDrop(info: DropInfo) -> Bool {
let _ = info.itemProviders(for: [.text]).first?.loadObject(ofClass: String.self) { item, error in
print("performDrop: \(item)") // Will trigger this
}
return true
}
}
Related
When I pop the view controller stack, I need a table view in the first view controller to reload. I am using viewWillAppear (I already tried viewDidAppear and it didn't work).
override func viewWillAppear(_ animated: Bool) {
print("will appear")
loadData()
}
Once the view controller has re-appeared, I need to query the API again which I am doing in another service class with a completion handler of course and then reloading the table view:
#objc func loadData() {
guard let userEmail = userEmail else { return }
apiRequest(userId: userEmail) { (queriedArticles, error) in
if let error = error {
print("error in API query: \(error)")
} else {
guard let articles = queriedArticles else { return }
self.articlesArray.removeAll()
self.articleTableView.reloadData()
self.articlesArray.append(contentsOf: articles)
DispatchQueue.main.async {
self.articleTableView.reloadData()
}
}
}
}
What happens is that I am able to pop the stack and see the first view controller BUT it has the same data as it did before. I expect there to be one more cell with new data and it doesn't appear. I have to manually refresh (using refresh control) to be able to query and load the new data.
Any idea what I am doing wrong?
I'm getting info from an API using the following function where I pass in a string of a word. Sometimes the word doesn't available in the API if it doesn't available I generate a new word and try that one.
The problem is because this is an asynchronous function when I launch the page where the value from the API appears it is sometimes empty because the function is still running in the background trying to generate a word that exists in the API.
How can I make sure the page launches only when the data been received from the api ?
static func wordDefin (word : String, completion: #escaping (_ def: String )->(String)) {
let wordEncoded = word.addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed)
let uri = URL(string:"https://dictapi.lexicala.com/search?source=global&language=he&morph=false&text=" + wordEncoded! )
if let unwrappedURL = uri {
var request = URLRequest(url: unwrappedURL);request.addValue("Basic bmV0YXlhbWluOk5ldGF5YW1pbjg5Kg==", forHTTPHeaderField: "Authorization")
let dataTask = URLSession.shared.dataTask(with: request) { (data, response, error) in
do {
if let data = data {
let decoder = JSONDecoder()
let empty = try decoder.decode(Empty.self, from: data)
if (empty.results?.isEmpty)!{
print("oops looks like the word :" + word)
game.wordsList.removeAll(where: { ($0) == game.word })
game.floffWords.removeAll(where: { ($0) == game.word })
helper.newGame()
} else {
let definition = empty.results?[0].senses?[0].definition
_ = completion(definition ?? "test")
return
}
}
}
catch {
print("connection")
print(error)
}
}
dataTask.resume()
}
}
You can't stop a view controller from "launching" itself (except not to push/present/show it at all). Once you push/present/show it, its lifecycle cannot—and should not—be stopped. Therefore, it's your responsibility to load the appropriate UI for the "loading state", which may be a blank view controller with a loading spinner. You can do this however you want, including loading the full UI with .isHidden = true set for all view objects. The idea is to do as much pre-loading of the UI as possible while the database is working in the background so that when the data is ready, you can display the full UI with as little work as possible.
What I'd suggest is after you've loaded the UI in its "loading" configuration, download the data as the final step in your flow and use a completion handler to finish the task:
override func viewDidLoad() {
super.viewDidLoad()
loadData { (result) in
// load full UI
}
}
Your data method may look something like this:
private func loadData(completion: #escaping (_ result: Result) -> Void) {
...
}
EDIT
Consider creating a data manager that operates along the following lines. Because the data manager is a class (a reference type), when you pass it forward to other view controllers, they all point to the same instance of the manager. Therefore, changes that any of the view controllers make to it are seen by the other view controllers. That means when you push a new view controller and it's time to update a label, access it from the data property. And if it's not ready, wait for the data manager to notify the view controller when it is ready.
class GameDataManager {
// stores game properties
// updates game properties
// does all thing game data
var score = 0
var word: String?
}
class MainViewController: UIViewController {
let data = GameDataManager()
override func viewDidLoad() {
super.viewDidLoad()
// when you push to another view controller, point it to the data manager
let someVC = SomeOtherViewController()
someVC.data = data
}
}
class SomeOtherViewController: UIViewController {
var data: GameDataManager?
override func viewDidLoad() {
super.viewDidLoad()
if let word = data?.word {
print(word)
}
}
}
class AnyViewController: UIViewController {
var data: GameDataManager?
}
Is there a notification mechanism for tooltips, so then key modifiers can be used to make them dynamic? I do not know of one so went about this path to capture the tooltip view being created and trying to trigger a redraw when a key event occurs.
I monitor key modifier(s) (in my app delegate); focusing on SHIFT here but any key modifier will do:
var localKeyDownMonitor : Any? = nil
var globalKeyDownMonitor : Any? = nil
var shiftKeyDown : Bool = false {
didSet {
let notif = Notification(name: Notification.Name(rawValue: "shiftKeyDown"),
object: NSNumber(booleanLiteral: shiftKeyDown));
NotificationCenter.default.post(notif)
}
}
which the app's startup process will install ...
// Local/Global Monitor
_ /*accessEnabled*/ = AXIsProcessTrustedWithOptions([kAXTrustedCheckOptionPrompt.takeUnretainedValue() as String: true] as CFDictionary)
globalKeyDownMonitor = NSEvent.addGlobalMonitorForEvents(matching: NSEventMask.flagsChanged) { (event) -> Void in
_ = self.keyDownMonitor(event: event)
}
localKeyDownMonitor = NSEvent.addLocalMonitorForEvents(matching: NSEventMask.flagsChanged) { (event) -> NSEvent? in
return self.keyDownMonitor(event: event) ? nil : event
}
and then intercept to post notifications via app delegate didSet above (so when the value changes a notification is sent!):
func keyDownMonitor(event: NSEvent) -> Bool {
switch event.modifierFlags.intersection(.deviceIndependentFlagsMask) {
case [.shift]:
self.shiftKeyDown = true
return true
default:
// Only clear when true
if shiftKeyDown { self.shiftKeyDown = false }
return false
}
}
For singleton tooltip bindings, this can be dynamic by having the notification inform (KVO of some key) I'd like a view delegate routine to act on this:
func tableView(_ tableView: NSTableView, toolTipFor cell: NSCell, rect: NSRectPointer, tableColumn: NSTableColumn?, row: Int, mouseLocation: NSPoint) -> String {
if tableView == playlistTableView
{
let play = (playlistArrayController.arrangedObjects as! [PlayList])[row]
if shiftKeyDown {
return String(format: "%ld play(s)", play.plays)
}
else
{
return String(format: "%ld item(s)", play.list.count)
}
}
...
So I'd like my notification handler to do something like
internal func shiftKeyDown(_ note: Notification) {
let keyPaths = ["cornerImage","cornerTooltip","<table-view>.<column-view>"]
for keyPath in (keyPaths)
{
self.willChangeValue(forKey: keyPath)
}
if subview.className == "NSCustomToolTipDrawView" {
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "CustomToolTipView"), object: subview)
}
for keyPath in (keyPaths)
{
self.didChangeValue(forKey: keyPath)
}
}
where I would like to force the tooltip to redraw, but nothing happens.
What I did to obtain the tooltip view, was to watch any notification (use nil name to do this) that looked promising and found one - by monitoring all notifications and so I post to it for interested view controller which is the delegate of the tableView. The view controller is observing for the "CustomToolTipView" and remembers the object send - tooltipView; this is the new tooltip view created.
But nothing happens - shiftKeyDown(), to redraw the view.
I suspect it won't update in the current event loop but I do see the debug output.
With Willeke's suggestion I migrated a tableView to be cell based, added a get property for the tooltip and had the relevant object's init() routine register notifications for the shift key changes. This resulted in less code. A win-win :-)
I was playing with Combine framework lately and was wondering if it is possible to create some smart extension to get text changes as Publisher.
Let's say I've got two UITextFields:
firstTextField.textPub.sink {
self.viewModel.first = $0
}
secondTextField.textPub.sink {
self.viewModel.second = $0
}
where first and second variable is just `#Published var first/second: String = ""
extension UITextField {
var textPub: AnyPublisher<String, Never> {
return NotificationCenter.default
.publisher(for: UITextField.textDidChangeNotification)
.map {
guard let textField = $0.object as? UITextField else { return "" }
return textField.text ?? ""
}
.eraseToAnyPublisher()
}
}
This doesn't work because I'm using shared instance of NotificationCenter so when I make any change to any of textFields it will propagate new value to both sink closures. Do you think is there any way to achieve something similar to rx.text available in RxSwift? I was thinking about using addTarget with closure but it would require using associated objects from Objective-C.
I figured this out. We can pass object using NotificationCenter and then filter all instances that are not matching our instance. It seems to work as I expected:
extension UITextField {
var textPublisher: AnyPublisher<String, Never> {
NotificationCenter.default
.publisher(for: UITextField.textDidChangeNotification, object: self)
.compactMap { $0.object as? UITextField }
.map { $0.text ?? "" }
.eraseToAnyPublisher()
}
}
I would suggest you add subscribers to the view modal, and connect them a text field publisher within the context of the view controller.
NotificationCenter is useful to dispatch events app-wide; there's no need to use it when connecting items that are fully owned by the View Controller. However, once you've updated the view modal it may make sense to publish a 'View Modal Did Change' event to NotificationCenter.
My view models are fundamentally flawed because those that use a driver will complete when an error is returned and resubscribing cannot be automated.
An example is my PickerViewModel, the interface of which is:
// MARK: Picker View Modelling
/**
Configures a picker view.
*/
public protocol PickerViewModelling {
/// The titles of the items to be displayed in the picker view.
var titles: Driver<[String]> { get }
/// The currently selected item.
var selectedItem: Driver<String?> { get }
/**
Allows for the fetching of the specific item at the given index.
- Parameter index: The index at which the desired item can be found.
- Returns: The item at the given index. `nil` if the index is invalid.
*/
func item(atIndex index: Int) -> String?
/**
To be called when the user selects an item.
- Parameter index: The index of the selected item.
*/
func selectItem(at index: Int)
}
An example of the Driver issue can be found within my CountryPickerViewModel:
init(client: APIClient, location: LocationService) {
selectedItem = selectedItemVariable.asDriver().map { $0?.name }
let isLoadingVariable = Variable(false)
let countryFetch = location.user
.startWith(nil)
.do(onNext: { _ in isLoadingVariable.value = true })
.flatMap { coordinate -> Observable<ItemsResponse<Country>> in
let url = try client.url(for: RootFetchEndpoint.countries(coordinate))
return Country.fetch(with: url, apiClient: client)
}
.do(onNext: { _ in isLoadingVariable.value = false },
onError: { _ in isLoadingVariable.value = false })
isEmpty = countryFetch.catchError { _ in countryFetch }.map { $0.items.count == 0 }.asDriver(onErrorJustReturn: true)
isLoading = isLoadingVariable.asDriver()
titles = countryFetch
.map { [weak self] response -> [String] in
guard let `self` = self else { return [] }
self.countries = response.items
return response.items.map { $0.name }
}
.asDriver(onErrorJustReturn: [])
}
}
The titles drive the UIPickerView, but when the countryFetch fails with an error, the subscription completes and the fetch cannot be retried manually.
If I attempt to catchError, it is unclear what observable I could return which could be retried later when the user has restored their internet connection.
Any justReturn error handling (asDriver(onErrorJustReturn:), catchError(justReturn:)) will obviously complete as soon as they return a value, and are useless for this issue.
I need to be able to attempt the fetch, fail, and then display a Retry button which will call refresh() on the view model and try again. How do I keep the subscription open?
If the answer requires a restructure of my view model because what I am trying to do is not possible or clean, I would be willing to hear the better solution.
Regarding ViewModel structuring when using RxSwift, during intensive work on a quite big project I've figured out 2 rules that help keeping solution scalable and maintainable:
Avoid any UI-related code in your viewModel. It includes RxCocoa extensions and drivers. ViewModel should focus specifically on business logic. Drivers are meant to be used to drive UI, so leave them for ViewControllers :)
Try to avoid Variables and Subjects if possible. AKA try to make everything "flowing". Function into function, into function and so on and, eventually, in UI. Of course, sometimes you need to convert non-rx events into rx ones (like user input) - for such situations subjects are OK. But be afraid of subjects overuse - otherwise your project will become hard to maintain and scale in no time.
Regarding your particular problem. So it is always a bit tricky when you want retry functionality. Here is a good discussion with RxSwift author on this topic.
First way. In your example, you setup your observables on init, I also like to do so. In this case, you need to accept the fact that you DO NOT expect a sequence that can fail because of error. You DO expect sequence that can emit either result-with-titles or result-with-error. For this, in RxSwift we have .materialize() combinator.
In ViewModel:
// in init
titles = _reloadTitlesSubject.asObservable() // _reloadTitlesSubject is a BehaviorSubject<Void>
.flatMap { _ in
return countryFetch
.map { [weak self] response -> [String] in
guard let `self` = self else { return [] }
self.countries = response.items
return response.items.map { $0.name }
}
.materialize() // it IS important to be inside flatMap
}
// outside init
func reloadTitles() {
_reloadTitlesSubject.onNext(())
}
In ViewController:
viewModel.titles
.asDriver(onErrorDriveWith: .empty())
.drive(onNext: [weak self] { titlesEvent in
if let titles = titlesEvent.element {
// update UI with
}
else if let error = titlesEvent.error {
// handle error
}
})
.disposed(by: bag)
retryButton.rx.tap.asDriver()
.drive(onNext: { [weak self] in
self?.viewModel.reloadTitles()
})
.disposed(by: bag)
Second way is basically what CloackedEddy suggests in his answer. But can be simplified even more to avoid Variables. In this approach you should NOT setup your observable sequence in viewModel's init, but rather return it anew each time:
// in ViewController
yourButton.rx.tap.asDriver()
.startWith(())
.flatMap { [weak self] _ in
guard let `self` = self else { return .empty() }
return self.viewModel.fetchRequest()
.asDriver(onErrorRecover: { error -> Driver<[String]> in
// Handle error.
return .empty()
})
}
.drive(onNext: { [weak self] in
// update UI
})
.disposed(by: disposeBag)
I would shift some responsibilities to the view controller.
One approach would be to have the view model produce an Observable which as a side effect updates the view model properties. In the following code example, the view controller remains in charge of the view bindings, as well as triggering the refresh in viewDidLoad() and via a button tap.
class ViewModel {
let results: Variable<[String]> = Variable([])
let lastFetchError: Variable<Error?> = Variable(nil)
func fetchRequest() -> Observable<[String]> {
return yourNetworkRequest
.do(onNext: { self.results.value = $0 },
onError: { self.lastFetchError.value = $0 })
}
}
class ViewController: UIViewController {
let viewModel = ViewModel()
let disposeBag = DisposeBag()
override func viewDidLoad() {
super.viewDidLoad()
viewModel.results
.asDriver()
.drive(onNext: { yourLabel.text = $0 /* .reduce(...) */ })
.disposed(by: disposeBag)
viewModel.lastFetchError
.asDriver()
.drive(onNext: { yourButton.isHidden = $0 == nil })
.disposed(by: disposeBag)
yourButton.rx.tap
.subscribe(onNext: { [weak self] in
self?.refresh()
})
.disposed(by: disposeBag)
// initial attempt
refresh()
}
func refresh() {
// trigger the request
viewModel.fetchRequest()
.subscribe()
.disposed(by: disposeBag)
}
}
All answers are good, but i want to mentioned about CleanArchitectureRxSwift. This framework really help me to find the way how rx can be applied to my code. The part about "backend" mobile programming (request, parsers, etc) can be omitted, but work with viewModel/viewController has really interesting things.