如何检测[在App-Delegate中]用户将视图从标准更改为缩放到iPhone的显示设置

Question

As much as i know when we switch between Standard and Zoomed view iphone restarts in background. I have some code in didFinishLaunchingWithOptions method for clearing keychain if its a fresh install. Now when ever i switch view[standard to zoomed] iOs treats it as a fresh install and clears keychain, thus making my application crash. Is there anyway to know in code that view is changed so i can stop application from reseting keychain. Here is the code snippet:

func application(_ application: UIApplication, didFinishLaunchingWithOptions 
    launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {

    //clear keychain for every fresh install
    if !Foundation.UserDefaults.standard.bool(forKey: Keys.kIsFreshInstall) {

        //delete keychain
        print("clearing keychain")
        EMKeychainUtil.clearKeychain()

        // update the flag indicator
        Foundation.UserDefaults.standard.set(true, forKey:Keys.kIsFreshInstall)
    }

    return true
}

UPDATE:

Whenever device restarts UserDefaults are not reseted.

There was a code in my project that was internally clearing the UserDefaults data first and then the check was made for keychain clearing , hence the issue was there.

Answer 1

In your appDelegate monitor UIScreen.mainScreen.nativeScale property (not scale )

The. scale will remain constant but nativeScale will go up / down with the zoom factor set

—

As for observing it: KVO would not work since any app is killed when changing zoom in settings. You may have to persist it if needed

Answer 2

You can use the following code :

[UIScreen mainScreen].scale

The scale size will be different when you changed from standard to zoomed.

Hope it will help!