如何将不在根层次结构中的 SwiftUI 视图呈现为 UIImage？

Question

假设我有一个简单的 SwiftUI 视图，它不是像这样的 ContentView：

struct Test: View {        
    var body: some View {
        VStack {
            Text("Test 1")
            Text("Test 2")
        }
    }
}

如何将此视图呈现为 UIImage？

我研究了解决方案，例如：

extension UIView {
    func asImage() -> UIImage {
        let renderer = UIGraphicsImageRenderer(bounds: bounds)
        return renderer.image { rendererContext in
            layer.render(in: rendererContext.cgContext)
        }
    }
}

但似乎这样的解决方案只适用于 UIView，而不适用于 SwiftUI 视图。

Answer 1

这是对我有用的方法，因为我需要将图像与其他图像放在一起时的大小完全相同。希望对其他人有帮助。

演示：上面的分隔线是 SwiftUI 渲染的，下面是图像（在边框中显示大小）

extension View {
    func asImage() -> UIImage {
        let controller = UIHostingController(rootView: self)

        // locate far out of screen
        controller.view.frame = CGRect(x: 0, y: CGFloat(Int.max), width: 1, height: 1)
        UIApplication.shared.windows.first!.rootViewController?.view.addSubview(controller.view)

        let size = controller.sizeThatFits(in: UIScreen.main.bounds.size)
        controller.view.bounds = CGRect(origin: .zero, size: size)
        controller.view.sizeToFit()

        let image = controller.view.asImage()
        controller.view.removeFromSuperview()
        return image
    }
}

extension UIView {
    func asImage() -> UIImage {
        let renderer = UIGraphicsImageRenderer(bounds: bounds)
        return renderer.image { rendererContext in
// [!!] Uncomment to clip resulting image
//             rendererContext.cgContext.addPath(
//                UIBezierPath(roundedRect: bounds, cornerRadius: 20).cgPath)
//            rendererContext.cgContext.clip()

// As commented by @MaxIsom below in some cases might be needed
// to make this asynchronously, so uncomment below DispatchQueue
// if you'd same met crash
//            DispatchQueue.main.async {
                 layer.render(in: rendererContext.cgContext)
//            }
        }
    }
}


// TESTING
struct TestableView: View {
    var body: some View {
        VStack {
            Text("Test 1")
            Text("Test 2")
        }
    }
}

struct TestBackgroundRendering: View {
    var body: some View {
        VStack {
            TestableView()
            Divider()
            Image(uiImage: render())
                .border(Color.black)
        }
    }
    
    private func render() -> UIImage {
        TestableView().asImage()
    }
}

struct TestBackgroundRendering_Previews: PreviewProvider {
    static var previews: some View {
        TestBackgroundRendering()
    }
}