从 Form/NavigationView 中的闭包引用属性并交换视图时，SwiftUI 内存泄漏

Question

I have something like this:

struct SomeView: View {
  @ObservedObject var viewModel: SomeViewModel

  var body: some View {
     NavigationView { // <- culprit
        Button(action: { self.viewModel.logOut() }) { Text("X").frame(width: 40, height: 40) }
     }
}

class SomeViewModel: ObservableObject {
  func logOut() {
  // changes global state, based on which the views are swapped, so `SomeView` is removed and replaced by a different one
  }
}

When the button is pressed, SomeView is closed and a different view is presented. But if I check the memory graph, SomeViewModel is still allocated because self.viewModel.logOut() is called in the Button's action closure and Button is holding the reference to SomeViewModel .

Is there some way around this?

EDIT: Actually, when not not wrapping the button in NavigationView , there is no leak. As soon as I wrap the button, the leak appears. Wrapping in VStack is working out fine. But wrapping in Form produces the leak again. Seems like the same problem here: SwiftUI - Possible Memory Leak

Answer 1

I found a solution: Make a weak viewModel in your action. It seems that Apple changed the behavior of closures. This means that the NavigationView is storing a strong reference to viewModel. After a couple days of debugging, it finally worked for me.

Button(action: { 
    [weak viewModel] in viewModel?.dismissButtonPressed.send(())
}) {
    Image("crossmark")
        .padding()
        .foregroundColor(Color.white)
    }
}

In your problem, this will be solved like this:

NavigationView { 
    [weak viewModel] in Button(action: { viewModel?.logOut() }) {
        Text("X").frame(width: 40, height: 40)
    }
}

Tested on the latest Xcode 11.5, with iOS 13.5. Now, after dismissing the view, the viewModel is correctly deallocated.