ios – How to define onTapGesture with debounce in SwiftUI using PassThroughSubject simpler way than modifier, ViewModifier and Model inside?

A debounce operation can be implemented by waiting inside a task(id:). Change the id parameter in onTapGesture to start a new task. If another tap occurs during the Task.sleep call, the task will be cancelled and so Task.sleep will throw an error.

struct DebounceTapModifier: ViewModifier {
    private let action: () -> Void
    private let debounce: CGFloat
    
    @State private var taskTrigger: Bool?
    
    init(action: @escaping () -> Void, debounce: CGFloat) {
        self.action = action
        self.debounce = debounce
    }
    
    func body(content: Content) -> some View {
        content
            .onTapGesture {
                taskTrigger = !(taskTrigger ?? false)
            }
            .task(id: taskTrigger) {
                guard taskTrigger != nil { return } // the user has not tapped yet
                do {
                    try await Task.sleep(for: .seconds(debounce))
                    // if Task.sleep throws an error, action will not be called
                    action()
                } catch {
                    // another tap occurred during the debounce duration
                }
            }
    }
}

As for your Combine approach, the lifetime of DebounceViewModel is not being managed by SwiftUI. I would make it an ObservableObject and put it in a @StateObject, so that its lifetime is the same as the view modifier.

class Debouncer: ObservableObject {
    var cancellable: (any Cancellable)?
    let subject = PassthroughSubject()
    
    deinit {
        print("deinit")
    }
}

struct DebounceTapModifier: ViewModifier {
    private let action: () -> Void
    private let debounce: CGFloat
    private var debouncer = Debouncer()
    
    init(action: @escaping () -> Void, debounce: CGFloat) {
        self.action = action
        self.debounce = debounce
    }
    
    func body(content: Content) -> some View {
        content
            .onTapGesture {
                debouncer.subject.send(0)
            }
            .onChange(of: debounce) {
                // redo the publisher subscription if the debounce time has changed
                // if debounce is always the same then you can just do this in onAppear
                setupActions()

                 // *do not* call setupActions in the initialiser. The StateObject has not yet been "installed" at that time.
            }
    }
    
    private func setupActions() {
        debouncer.cancellable = debouncer.subject
            .debounce(for: .seconds(debounce), scheduler: DispatchQueue.main)
            .sink { _ in
                action()
            }
    }
}