My assumption is it works similar to UIView’s/NSView’s setNeedsDisplay() (docs) - https://developer.apple.com/documentation/uikit/uiview/1622437-setneedsdisplay: The view is not actually redrawn until the next drawing cycle, at which point all invalidated views are updated. So objectWillChange schedules an update, which occurs in SwiftUI’s equivalent of the next drawing cycle.