When accessing the settings to enable access to a feature of device, why should I use

Question

I'm slightly confused as to which way is best to access the settings to enable a device feature if access has been denied before. I have seen two ways which one seems to be using threading. But I haven't found a clear explanation as to why? Would appreciate any insight on this. Thanks.

Both works , either the snippet below as an action of an alert controller:

alert.addAction(UIAlertAction(title: "Settings", style: .default, handler: {(_ action: UIAlertAction) -> Void in
            //open settings to allow access to geo
            guard let stngUrl = URL(string: UIApplicationOpenSettingsURLString) else {
                return
            }
            if UIApplication.shared.canOpenURL(stngUrl) {
                if #available(iOS 10.0, *) {
                    UIApplication.shared.open(stngUrl, completionHandler: { (success) in
                    })
                } else {
                    if UIApplication.shared.canOpenURL(stngUrl) {
                        UIApplication.shared.openURL(stngUrl)
                    }
                }
            }                
        }))
        present(alert, animated: true, completion: nil)

or using DispatchQueue like snippet below?

 alert.addAction(UIAlertAction(title: "Settings", style: .default, handler: {(_ action: UIAlertAction) -> Void in            
        DispatchQueue.main.async(execute: {() -> Void in
            UIApplication.shared.openURL(URL(string: UIApplicationOpenSettingsURLString)!)
        })
    }))
    present(alert, animated: true, completion: nil)

Answer 1

There is no reason to use DispatchQueue.main in the handler of a UIAlertAction because the handler will always be called on the main thread. So it's redundant to use DispatchQueue.main.