iOS 14 .onAppear() is called on DISappear instead of appear

Question

Emnasut OP

Created Jul ’20

Replies 36

Boosts 2

Views 22k

Participants 38

I've got a View with

Code Block .onAppear(perform: {
	print("appear")
})
.onDisappear(perform: {
	print("disappear")
})

set on it.

In iOS 13.5, when I navigate away from the view via a NavigationLink, it prints "disapear"; when I close the new view and get back to the first view "appear" gets printed. All as it should be.

Now in iOS 14, this happens instead:

when the view is first shown, it prints "appear"
when navigating away from the view, it prints "disappear" and "appear"
when navigating back to the view, nothing gets printed
when navigating away from the view, then "appear" gets printed, along with the expected "disappear"

...is this some new super-lazy way of doing things or just plain a bug?

It runs havoc with my login, as I set @Binding vars in the second view, which are evaluated back in the first view when .onAppear() runs. Worked great until iOS 14...

Boost

Answer 1

relamquad OP

Nov ’20

Create issue, thanks UIKit))

Code Block struct UIKitAppear: UIViewControllerRepresentable {
    let action: () -> Void
    func makeUIViewController(context: Context) -> UIAppearViewController {
       let vc = UIAppearViewController()
        vc.action = action
        return vc
    }
    func updateUIViewController(_ controller: UIAppearViewController, context: Context) {
    }
}
class UIAppearViewController: UIViewController {
    var action: () -> Void = {}
    override func viewDidLoad() {
        view.addSubview(UILabel())
    }
    override func viewDidAppear(_ animated: Bool) {
        action()
    }
}
public extension View {
    func uiKitOnAppear(_ perform: @escaping () -> Void) -> some View {
        self.background(UIKitAppear(action: perform))
    }
}

Example:

Code Block var body: some View {
	SomeView().uiKitOnAppear {
     print("I am uiKitAppear")
   }
}

9

Answer 2

Heidi0039 OP

Nov ’20

Any Update here?
I can't seem to find an acceptable workaround.

I am using xCode 12.2 and am still experiencing this issue

3

Answer 3

sivaprasad-kiranum OP

Nov ’20

This issue happens in Xcode Version 12.2 (12B45b) and iOS 14.2. Is there any workaround for this issue?

2

Answer 4

sobri OP

Nov ’20

Echoing everyone else: This issue is still painfully present, and there's no known workaround. Something needs to happen. This is not okay.

3

Answer 5

yes boy OP

Nov ’20

Found a weird quirk. When you pass in the method directly (line 9/10) it's a lot more stable.

Code Block swift
.onAppear {
	viewModel.onAppear()
}
.onDisappear {
	viewModel.onDisappear()
}
.onAppear(perform: viewModel.onAppear)
.onDisappear(perform: viewModel.onDisappear)

1

Answer 6

mobile_development@stendahls OP

Dec ’20

Just found out that it works correctly on iOS 14 if you have parentheses after onAppear/onDisappear:

Code Block Swift.onAppear() {
	print("...code here")
}
.onDisappear() {
	print("...code here")
}

0

Answer 7

marvzi OP

Dec ’20

Is there any update? I cannot believe that this is not working. Is there a new way of using these lifecycle methods?

2

Answer 8

Broker89 OP

Jan ’21

Hi Guys, I don't have a nativ fix for this problem but a workaround I have found after 3 days of research which I have posted here: https://stackoverflow.com/a/65857640/6131259 I hope it helps some of you.

1

Answer 9

basememara OP

Jan ’21

On Xcode 12.3 / iOS 14.3 and onAppear is still very flaky. I'm actively avoiding it at all costs everywhere and calling functions manually while constructing the view instead.

1

Answer 10

canhcutvl OP

Jan ’21

Only relamquad's answer with UIKit gave me the most confidence and it works. With the flakiness from version to version for SwiftUI's onAppear, just a simple syntax change and everything stops working, relying solely on SwiftUI is too risky. I can't believe this is not high on the bug list. onAppear is such an essential part

3

Answer 11

NBCFF OP

Apr ’21

Was using relamquad's answer quite successfully until I noticed it can lead to memory leaks due to strong reference cycles.

Using it like described works fine:

Code Block Swiftvar body: some View {	
  SomeView().uiKitOnAppear {
    print("I am uiKitAppear")   
  }
}

However if you pass a ViewModel's function for example, the ViewModel will not be deallocated once the View should be deinitialized:

Code Block Swift@ObservedObject var viewModel: ViewModel
var body: some View {	
  SomeView().uiKitOnAppear {
    viewModel.startUpdating()  
  }
}

If been trying to find a solution using weak references, but then again, somehow startUpdating is not called on .uiKitOnAppear().
Does anybody know a solution to this?

0

Answer 12

gfdgdfg OP

Apr ’21

Code Block import SwiftUI
struct UIKitAppear: UIViewControllerRepresentable {
    let action: () -> Void
    func makeUIViewController(context: Context) -> UIAppearViewController {
       let vc = UIAppearViewController()
        vc.delegate = context.coordinator
        return vc
    }
    func updateUIViewController(_ controller: UIAppearViewController, context: Context) {}
    func makeCoordinator() -> Coordinator {
        Coordinator(action: self.action)
    }
    class Coordinator: ActionRepresentable {
        var action: () -> Void
        init(action: @escaping () -> Void) {
            self.action = action
        }
        func remoteAction() {
            action()
        }
    }
}
protocol ActionRepresentable: AnyObject {
    func remoteAction()
}
class UIAppearViewController: UIViewController {
    weak var delegate: ActionRepresentable?
    override func viewDidLoad() {
        view.addSubview(UILabel())
    }
    override func viewDidAppear(_ animated: Bool) {
        delegate?.remoteAction()
    }
}
public extension View {
    func onUIKitAppear(_ perform: @escaping () -> Void) -> some View {
        self.background(UIKitAppear(action: perform))
    }
}

0

Answer 13

NBCFF OP

Apr ’21

Thanks gfdgdfg for the quick response and solution proposition.

In my specific case, it did not solve the memory leak issue. What helped was resetting the action in updateUIViewController(_ controller: UIAppearViewController, context: Context).

Extending relamquad's answer like this:

Code Block swiftstruct UIKitAppear: UIViewControllerRepresentable {
    let action: () -> Void
    func makeUIViewController(context: Context) -> UIAppearViewController {
        let vc = UIAppearViewController()
        vc.action = action
        return vc
    }
    func updateUIViewController(_ controller: UIAppearViewController, context: Context) {
        controller.action = action
    }
}

0

Answer 14

Graviton27 OP

Apr ’21

I found that the issue with .onAppear exist only when I using ObservedObject in my View if I change it to the StateObject the problem is gone but I need to support an iOS 13 so as the temporary solution I calling my API call inside init of my view

0

Answer 15

SidAnIosDeveloper OP

May ’21

Can someone please fix this? It's just so dumb! .onAppear() is very very wonky. Did you guys not even review the PRs before pushing out the commits? And the worst thing is .onDisappear() doesn't work at all.

0