Set custom UIView frame in UIViewRepresentable SwiftUI

Question

I'm trying to use my custom UIView in SwiftUI using UIViewRepresentable and I want my UIView to have the same size as I set in .frame() so that I can use it like this:

MyViewRepresentable()
.frame(width: 400, height: 250, alignment: .center)

For example, I can set a frame as a property:

struct MyViewRepresentable: UIViewRepresentable {
    var frame: CGRect
    func makeUIView(context: Context) -> UIView {
        let myView = MyView(frame: frame)

        return view
    }
    func updateUIView(_ uiView: UIView, context: Context) {}
}

Usage:

struct ContentView: View {
    var body: some View {
        MyViewRepresentable(frame: CGRect(x: 0, y: 0, width: 400, height: 250))
            .frame(width: 400, height: 250, alignment: .center)
    }
}

It is not a solution and I wonder how to make it right.

Answer 1

If MyView has correct internal layout (which depends only on own bounds), then there is not needs in external additional limitation, ie

struct MyViewRepresentable: UIViewRepresentable {
    func makeUIView(context: Context) -> UIView {
        return MyView(frame: .zero)
    }
    func updateUIView(_ uiView: UIView, context: Context) {}
}

will be exactly sized below having 400x250 frame

struct ContentView: View {
    var body: some View {
        MyViewRepresentable()
            .frame(width: 400, height: 250, alignment: .center)
    }
}

if it is not then internal MyView layout has defects.

Answer 2

If Asperi's answer did not work out for you, then it's probably as they said: the internal MyView layout has defects.

To resolve this matter, you have a couple options:

Option A. Use AutoLayout Constraints within viewDidLoad

override func viewDidLoad() {
    super.viewDidLoad()

    // 1. View Hierarchy
    self.addChild(self.mySubview)
    self.view.addSubview(self.mySubview.view)
    self.mySubview.didMove(toParent: self)
    
    // 2. View AutoLayout Constraints
    self.mySubview.view.translatesAutoresizingMaskIntoConstraints = false
    NSLayoutConstraint.activate([
        view.leadingAnchor.constraint(equalTo: self.mySubview.view.leadingAnchor),
        view.trailingAnchor.constraint(equalTo: self.mySubview.view.trailingAnchor),
        view.topAnchor.constraint(equalTo: self.mySubview.view.topAnchor),
        view.bottomAnchor.constraint(equalTo: self.mySubview.view.bottomAnchor)
    ])
}

Option B. Set frame manually within viewDidLayoutSubviews

Simply within your UIViewController, set subviews frames in viewDidLayoutSubviews.

override func viewDidLoad() {
    super.viewDidLoad()

    // 1. Add your subviews once in `viewDidLoad`
    self.addChild(self.mySubview)
    self.view.addSubview(self.mySubview.view)
    self.mySubview.didMove(toParent: self)
}

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()

    // 2. Layout your subviews `viewDidLayoutSubviews`
    // Update subview frame size
    // Must be done in `viewDidLayoutSubviews`
    // Otherwise in `viewDidLoad` the bounds equal `UIScreen.main.bounds`, even if you used explicit frame within SwiftUI and used GeometryReader to pass the `CGSize` yourself to this UIViewController!
    let mySubviewFrame = self.view.bounds
    self.mySubview.view.frame = mySubviewFrame
}

Supplementary Resources

• Basically you have multiple layout methods in iOS. Here they are ordered from oldest/worst to newest/best. This ordering is opinionated of course:
  • Frame-Based Layout. Manually manipulate frame and bounds properties on the UIView.
  • Auto-Resizing Masks. Under the hood, an autoResizingMask uses archaic springs and struts. See autoResizingMask, this answer, and this article.
  • AutoLayout Constraints.
  • AutoLayout StackView.
  • SwiftUI's VStack and HStack! This is only for SwiftUI and all the above applies to UIKit only.

_{Probably should have made a small dev article out of this.}