ViewVisibility

Extends SwiftUI/View with the onVisibilityChange(in:scale:perform:) modifier, allowing you to track the "visibility" of a view on the screen and execute an action when its visibility state changes.

Motivation

When it comes to determining whether a view is "visible" on the screen, the system's onAppear doesn't always provide reliable results (hello, TabView). Additionally, in some cases, it's important to know whether a view is fully visible, partially visible (e.g., at least half of its height), or completely off-screen. That's why I created onVisibilityChange(in:scale:perform:), which has been tested on iOS 16.

Usage

You provide a rectangle via the in parameter to define the area in which visibility should be checked, such as UIScreen.main.bounds. By default, the system compares the view’s frame against this rectangle, but you can modify the frame size using the scale parameter. Whenever the view's visibility state changes, the perform(Bool) closure is triggered.

Note

Avoid using this modifier in environments with frequent updates for a large number of views (e.g., ScrollView), as it relies on onGeometryChange(), which is computed on every geometry change.

ScrollView {
    RoundedRectangle(cornerRadius: 20)
        .frame(width: 200, height: 400)
        .padding(10) // ⚠️ padding will be included in `visibility` rect
        .onVisibilityChange(
            in: UIScreen.main.bounds,
            scale: 0.9
        ) { visible in
            print(visible ? "✅ visible" : "❌ hidden")
        }
}