Swift UI: UIHostingController.view is not fit to content view size at iOS 13

Question

I want to update Swift UI View according to the communication result. But UIHostingController.view is not fit rootView size at iOS 13. The same thing happens when I try with the sample code below. I want to add self-sizing SwiftUI View to UIStackView, but SwiftUI View overlaps with the previous and next views is occurring because this problem. How can I avoid this problem?

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        let object = SampleObject()
        let sampleView = SampleView(object: object)
        let hosting = UIHostingController(rootView: sampleView)
        hosting.view.backgroundColor = UIColor.green
        addChild(hosting)
        view.addSubview(hosting.view)
        hosting.view.translatesAutoresizingMaskIntoConstraints = false
        hosting.view.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
        hosting.view.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
        hosting.view.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
        hosting.didMove(toParent: self)
        
        DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) {
            object.test()
        }
    }
}


struct SampleView: View {
    @ObservedObject var object: SampleObject
    
    var body: some View {
        VStack {
            Text("test1").background(Color.blue)
            Text("test2").background(Color.red)
            if object.state.isVisibleText {
                Text("test2").background(Color.gray)
            }
        }
        .padding(32)
        .background(Color.yellow)
    }
}


final class SampleObject: ObservableObject {
    struct ViewState {
        var isVisibleText: Bool = false
    }
    
    @Published private(set) var state = ViewState()
    
    func test() {
        state.isVisibleText = true
    }
}

If addSubview to UIStackView as below, the height of Swift UI View will not change in iOS13.

iOS13 (incorrect)

iOS14 (correct)

Greathouse

Answer 1

Only for iOS 13

Try this:

Every time the view size change, call this:

sampleView.view.removeFromSuperview()
let sampleView = SampleView(object: object)
let hosting = UIHostingController(rootView: sampleView)
view.addArrangedSubview(hosting.view)

Hostile

Yes, I didn't mention it, but I fixed it that way. – Daddylonglegs

Answer 2

You have not set the bottom anchor, add this line

hosting.view.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true

Another easy way is to set frame to hosting controller view and remove the constraint.

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        let object = SampleObject()
        let sampleView = SampleView(object: object)
        let hosting = UIHostingController(rootView: sampleView)
        hosting.view.frame = UIScreen.main.bounds //<---here
        hosting.view.backgroundColor = UIColor.green
        addChild(hosting)
        view.addSubview(hosting.view)
        hosting.didMove(toParent: self)
        
        DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) {
            object.test()
        }
    }
}

Disclaim

With this workaround, the screen size and Swift UI View size will be the same. But I want the size of Swift UI View to be self-sizing. – Daddylonglegs

can you add an image for what you want? – Disclaim

I want to make it look like the attached iOS 14 image. i.sstatic.net/Q2SUq.jpg – Daddylonglegs

I added description & ScreenShot. Please check it. – Daddylonglegs

@RajaKishan is totally right - you have to add top + bottom + leading + trailing constraints. – Blimey

if add top + bottom + leading + trailing constraints, SampleView's size is equal to ViewController.view's size. But I want SampleView to decide its own size. I don't want it to be displayed large in the center. I want to display in the minimum required size. – Daddylonglegs

UIViewController.view doesn't have any default size/constraints, so if you add child view with all constraints then this child will decide the size of parent view (you can test this with UIKit views). However in your case I think there is a bug in iOS 13. UIStackView doesn't listen to SwiftUI views changes. I tried several approaches and nothing worked, but everything works fine on iOS 14. – Blimey

Yes, I also think it's a bug in iOS 13.There is no direct solution to this problem, so I'm looking for a workaround. – Daddylonglegs