zeveisenberg / customdynamicproperties

Custom Dynamic Properties

This project demonstrates how to make a custom DynamicProperty that will cause a SwiftUI View to rebuild it self when the property updates.

There are 2 steps to creating a dynamic property:

• Declare a @propertyWrapper that conforms to DynamicProperty.
• Add a @StateObject to the wrapper that is used to back the wrappedValue for the property wrapper.

Whenever the @StateObject emits an objectWillChange event (ie through a change to one of its @Published properties), the subscribed property wrapped will cause the View to update. This happens through the default implmentation of DynamicProperty's update function, which is provided by Apple.

https://developer.apple.com/documentation/swiftui/dynamicproperty

This project provides two sample custom @propertyWrapper's:

Interval

@Interval is a property wrapper that provides a timer that updates with the elapsed time.

@Interval(seconds: 1) private var time: TimeInterval

It provides methods to stop and reset as well as start the timer:

.onAppear { _time.start() }
.onDisappear { _time.stop() }

Notify

@Interval is a property wrapper that can subscribe to any Foundation.Notification and transform it into another type (such as by inspecting its userInfo dictionary).

@Notify(
notificationName: UIApplication.userDidTakeScreenshotNotification,
transform: { _ in Date() }
) private var screenshotDate: Date?