struct SizePreferenceKey: PreferenceKey {
static var defaultValue: CGSize = .zero
static func reduce(value: inout CGSize, nextValue: () -> CGSize) {}
}
extension View {
func readSize(onChange: @escaping (CGSize) -> Void) -> some View {
background(
GeometryReader { geometryProxy in
Color.clear
.preference(key: SizePreferenceKey.self, value: geometryProxy.size)
}
)
.onPreferenceChange(SizePreferenceKey.self, perform: onChange)
}
}
예시
Rectangle()
.foregroundColor(Color.red)
.frame(maxWidth: .infinity, maxHeight: .infinity)
.readSize { new in
print(new)
}