iosswiftswiftui

SwiftUI ColorScheme changes when app is backgrounded

I have a basic project reading the environment variable for ColorScheme, what i noticed is given my app is in light mode, when I background the app, the color scheme always switches between dark and light even if I never change the color mode.

  struct ContentView: View {
      @SwiftUI.Environment(\.colorScheme) var colorScheme

      var body: some View {
          VStack {
              let _ = Self._printChanges()
              let _ = print("====== colorscheme \(colorScheme)")
              Image(systemName: "globe")
                  .imageScale(.large)
                  .foregroundStyle(.tint)
              Text("Hello, world!")
          }
          .padding()
      }
  }

when i background the app it prints

ContentView: _colorScheme changed.
====== colorscheme dark
ContentView: _colorScheme changed.
====== colorscheme light

Has anyone noticed this issue? this a bug or design? and how to stop that from happening?

Solution

  • This is correct and is by design. When your app moves to the background, iOS needs to save a screen image for use in the app switcher.

    Since the device may switch between light/dark mode while your app is in the background it grabs two screen images; One in light mode and one in dark mode.

    iOS then uses the appropriate image in the switcher depending on the current scheme.

    You can't prevent this from happening.