This PR deprecates the publisher property for the StateContainer class and the @ViewState and @RenderedViewState property wrappers. It replaces the publisher property with two new properties called willSetPublisher and didSetPublisher that more accurately and explicitly indicate the publisher's timing.
Reasoning
During early use of the new @ViewState and @RenderedViewState property wrappers, it was discovered that when observing the state changes in a SwiftUI view via onReceive, the body property had already been evaluated for this state change because it was happening on the underlying StateContainer's willSet event. This means that if an engineer then modifies any SwiftUI view property (i.e., @State, @ObservedObject, etc.) it will cause the body property to be reevaluated, wasting resources and potentially causing timing bugs. In cases where the view state is progressed within the onReceive property, is is possible to cause infinite recursion.
As a result, the willSet and didSet event publishers were created so that engineers could have more fine-grained control over the timing of the state observation code.
Description
This PR deprecates the
publisherproperty for theStateContainerclass and the@ViewStateand@RenderedViewStateproperty wrappers. It replaces thepublisherproperty with two new properties calledwillSetPublisheranddidSetPublisherthat more accurately and explicitly indicate the publisher's timing.Reasoning
During early use of the new
@ViewStateand@RenderedViewStateproperty wrappers, it was discovered that when observing the state changes in a SwiftUI view viaonReceive, thebodyproperty had already been evaluated for this state change because it was happening on the underlying StateContainer'swillSetevent. This means that if an engineer then modifies any SwiftUI view property (i.e.,@State,@ObservedObject, etc.) it will cause thebodyproperty to be reevaluated, wasting resources and potentially causing timing bugs. In cases where the view state is progressed within theonReceiveproperty, is is possible to cause infinite recursion.Example Problem Scenario (Credit: @mlarandeau)
As a result, the willSet and didSet event publishers were created so that engineers could have more fine-grained control over the timing of the state observation code.
Type of Change
Checklist