Small library for lightweight UIView and UIViewController state management on iOS.
- Xcode 11.4
- Swift 5.2
- iOS 12
Installation supported by Swift Package Manager in Xcode 11 or higher:
https://github.com/Rightpoint/ViewState.git
import ViewState
final class ViewController: UIViewController {
struct ViewState: ViewStateProtocol {
var labelText: String = ""
var labelColor: UIColor = .black
}
@Observed
var state: ViewState
private let label = UILabel()
}
extension ViewController: HasViewState {
func render(state: ViewState, oldState: ViewState?, animated: Bool) {
label.text = state.labelText
label.textColor = state.labelColor
}
}Then whenever you want to update your view's state:
func startLoading() {
state.labelText = "Loading..."
}
func showError() {
state.update {
$0.labelText = "Ooops"
$0.labelColor = .red
}
}For any UIView or UIViewController subclass, make a nested struct called ViewState and conform it to ViewStateProtocol. It must support an empty initializer, so provide some sane default values. All properties must be Equatable.
final class ViewController: UIViewController {
struct ViewState: ViewStateProtocol {
var labelText: String = ""
var labelColor: UIColor = .black
}
To keep things minimal, only add properties here that are intended to be dynamic.
Then conform the parent type to HasViewState. The render function should be the only place that updates the dynamic values of your subviews.
final class ViewController: UIViewController {
@Observed
var state: ViewState
}
extension ViewController: HasViewState {
func render(state: ViewState, oldState: ViewState?, animated: Bool) {
label.text = state.labelText
label.textColor = state.labelColor
}
}You can use @Observed to annotate your state in a UIView or UIViewController
that conforms to HasViewState to automatically render when the state is updated.
For example:
@Observed
var state: ViewStateUnfortunately referencing the enclosing self in property wrapper
is still not a public API in Swift, so this might break in the future. If this is a concern, you can instead manually call renderIfNeeded in a didSet:
var state = ViewState() {
didSet {
renderIfNeeded(state: state, oldState: oldValue)
}
}To add easy SwiftUI support to your views, simply conform your ViewState to UIViewControllerRepresentable or UIViewRepresentable.
@available(iOS 13.0, *)
extension ViewController.ViewState: UIViewControllerRepresentable {
typealias UIViewControllerType = ViewController
}The main caveat here is that your UIView or UIViewController subclasses cannot have a non-empty designated initializer or you'll get a crash at runtime.
When your ViewStates are bridged to SwiftUI, it makes it easy to iterate by utilitizing Xcode Previews.
@available(iOS 13.0, *)
struct ViewController_Previews: PreviewProvider {
static var previews: some View {
Group {
ViewController.ViewState(
labelText: "Test 1"
).previewDevice("iPhone 11 Pro Max")
ViewController.ViewState(
labelText: "Test 2",
labelColor: .blue
).previewDevice("iPhone SE")
}
}
}If you have a custom non-empty designated initializer, you might want to use something like UIViewControllerPreview in your project instead of conforming to UIViewControllerRepresentable.
Issues and pull requests are welcome! Please ensure that you have the latest SwiftLint installed before committing and that there are no style warnings generated when building.
Contributors are expected to abide by the Contributor Covenant Code of Conduct.
Chris Ballinger: cballinger@rightpoint.com
ViewState is available under the MIT license. See the LICENSE file for more info.