Prevent iOS from taking screen capture of app before going into background

Question

You all might know that iOS takes a screen shot of your application before throwing it into the background. This is usually for a better User experience like quick animation

Answer 1

Working methods in AppDelegate, swift 4.2:

func blurScreen(style: UIBlurEffect.Style = UIBlurEffect.Style.regular) {
    screen = UIScreen.main.snapshotView(afterScreenUpdates: false)
    let blurEffect = UIBlurEffect(style: style)
    let blurBackground = UIVisualEffectView(effect: blurEffect)
    screen?.addSubview(blurBackground)
    blurBackground.frame = (screen?.frame)!
    window?.addSubview(screen!)
}

func removeBlurScreen() {
    screen?.removeFromSuperview()
}

Where is:

weak var screen : UIView? = nil // property of the AppDelegate

Call these methods in needed delegate methods:

func applicationWillResignActive(_ application: UIApplication) {
    blurScreen()
}

func applicationDidBecomeActive(_ application: UIApplication) {
    removeBlurScreen()
}

Answer 2

Apple Doc https://developer.apple.com/library/archive/qa/qa1838/_index.html

Note: Your implementation of -applicationDidEnterBackground: should not start any animations (pass NO to any animated: parameter). The snapshot of your application's window is captured immediately upon returning from this method. Animations will not complete before the snapshot is taken.

Converted Apple code in swift 4.2 App delegate i declared

func applicationDidEnterBackground(_ application: UIApplication) {
    // Your application can present a full screen modal view controller to
    // cover its contents when it moves into the background. If your
    // application requires a password unlock when it retuns to the
    // foreground, present your lock screen or authentication view controller here.

    let blankViewController = UIViewController()
    blankViewController.view.backgroundColor = UIColor.black

    // Pass NO for the animated parameter. Any animation will not complete
    // before the snapshot is taken.
    window.rootViewController?.present(blankViewController, animated: false)
}

func applicationWillEnterForeground(_ application: UIApplication) {
    // This should be omitted if your application presented a lock screen
    // in -applicationDidEnterBackground:
    window.rootViewController?.dismiss(animated: false) false
}

Answer 3

Your approach is exactly the correct and only way to do it. Place an overlay view and remove it later. It is valid to do this if your app shows sensitive data that you don't want to be cached in image format anywhere.

Answer 4

swift 4.0 version.

for use custom icon

first add this line at top of AppDelegate

var imageView: UIImageView?

and add this:

func applicationDidEnterBackground(_ application: UIApplication) {
    imageView = UIImageView(frame: window!.frame)
    imageView?.image = UIImage(named: "AppIcon")
    window?.addSubview(imageView!)
}

func applicationWillEnterForeground(_ application: UIApplication) {
    if imageView != nil {
        imageView?.removeFromSuperview()
        imageView = nil
    }
}

background with black color

func applicationDidEnterBackground(_ application: UIApplication) {
    let blankViewController = UIViewController()
    blankViewController.view.backgroundColor = UIColor.black
    window?.rootViewController?.present(blankViewController, animated: false)
}

func applicationWillEnterForeground(_ application: UIApplication) {
    window?.rootViewController?.dismiss(animated: false)
}