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SwiftUI: discover underlying components to fill in gaps in SwiftUI api
struct Test: View {
var body: some View {
List {
ForEach(1...5, id: \.self) { value in
Text("\(value)")
.listRowBackground(Color.blue)
}
}
.discover { (scrollView: UIScrollView) in
scrollView.backgroundColor = .red
}
}
}
import SwiftUI
extension View {
public func discover<T: UIView>(
tag: Int = .random(in: (.min)...(.max)),
where predicate: @escaping (T) -> Bool = { _ in true },
_ closure: @escaping (T) -> Void
) -> some View {
self.overlay(
DiscoveryView(tag: tag)
.frame(width: 0, height: 0)
.onAppear {
DispatchQueue.main.async {
let keyWindow = UIApplication.shared.windows.first(where: \.isKeyWindow)
let root = keyWindow?.viewWithTag(tag)
guard
let host = root.flatMap(findViewHost(from:)),
let discovered = findClosestView(T.self, host: host, where: predicate)
else {
return print("⚠️ Unable to find a view of type '\(T.self)'")
}
closure(discovered)
}
}
)
}
}
extension View {
public func discover<T: UIViewController>(
where predicate: @escaping (T) -> Bool = { _ in true },
_ closure: @escaping (T) -> Void
) -> some View {
var match: T?
return discover(
where: { (view: UIView) in
guard let controller = view.findViewController() else { return false }
let responderChain = sequence(first: controller, next: \.next)
for item in responderChain {
if let controller = item as? T, predicate(controller) {
match = controller
return true
}
}
return false
},
{ _ in
guard let controller = match else {
return print("⚠️ Unable to find a view controller of type '\(T.self)'")
}
closure(controller)
}
)
}
}
private extension UIView {
func findViewController() -> UIViewController? {
if let next = next as? UIViewController {
return next
} else if let next = next as? UIView {
return next.findViewController()
} else {
return nil
}
}
}
private struct DiscoveryView: UIViewRepresentable {
var tag: Int
func makeUIView(context: Context) -> some UIView {
let view = UIView()
view.frame = .zero
view.isUserInteractionEnabled = false
view.backgroundColor = .clear
view.tag = tag
return view
}
func updateUIView(_ uiView: UIViewType, context: Context) { }
}
private func findViewHost(from entry: UIView) -> UIView? {
var superview = entry.superview
while let s = superview {
if NSStringFromClass(type(of: s)).contains("ViewHost") {
return s
}
superview = s.superview
}
return nil
}
private func findClosestView<T: UIView>(_: T.Type = T.self, host: UIView, where predicate: @escaping (T) -> Bool) -> T? {
// find the view hosts index in it's superview
// search from that index back to 0
// - look down the hierarchy at each item for T
guard
let superview = host.superview,
let index = superview.subviews.firstIndex(of: host)
else { return nil }
let branches = superview.subviews[0...index].reversed()
return branches.lazy.compactMap({ $0.firstView(T.self, where: predicate) }).first
}
private extension UIView {
func firstView<T: UIView>(_: T.Type = T.self, where predicate: @escaping (T) -> Bool = { _ in true }) -> T? {
if let result = self as? T, predicate(result) {
return result
}
return subviews.lazy
.compactMap { $0.firstView(where: predicate) }
.first
}
}
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