home page jump over login feature in Swift - ios

Question

I am pretty new to the swift, I am trying to implement the feature that when the user logged in, they will get directly to the home page rather than the login page every time they reopen the app.
I took the reference to the tutorial: https://www.youtube.com/watch?v=gjYAIXjpIS8&t=146s. and I implemented the is logged in boolean checking as he did, but I somehow encounter the trouble reopen the homepage while logged in. I have an error message:[Presentation] Attempt to present <UITabBarController: 0x7fa68102ea00> on <IFTTT.ViewController: 0x7fa67fe0c150> (from <IFTTT.ViewController: 0x7fa67fe0c150>) whose view is not in the window hierarchy.
This is how my login page controller class:(which is the entry point when opening the app) I tried present as the tutorial and performsegue and both shows up the same error message above
import UIKit
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
if isLoggedIn() {
performSegue(withIdentifier: "logInJump", sender: nil)
}
}
fileprivate func isLoggedIn() -> Bool {
print("logged in status: \(UserDefaults.standard.bool(forKey: "isLoggedIn"))")
return UserDefaults.standard.bool(forKey: "isLoggedIn")
}
#IBAction func signInButton(_ sender: Any) {
print("sign in tapped")
if let appURL = URL(string: "http://vocation.cs.umd.edu/flask/register") {
UIApplication.shared.open(appURL) { success in
if success {
print("The URL was delivered successfully.")
} else {
print("The URL failed to open.")
}
}
} else {
print("Invalid URL specified.")
}
}
}
// button broder width
#IBDesignable extension UIButton {
#IBInspectable var borderWidth: CGFloat {
set {
layer.borderWidth = newValue
}
get {
return layer.borderWidth
}
}
#IBInspectable var cornerRadius: CGFloat {
set {
layer.cornerRadius = newValue
}
get {
return layer.cornerRadius
}
}
#IBInspectable var borderColor: UIColor? {
set {
guard let uiColor = newValue else { return }
layer.borderColor = uiColor.cgColor
}
get {
guard let color = layer.borderColor else { return nil }
return UIColor(cgColor: color)
}
}
}
and this is my messy story board and segues :
story board
I tried adding a navigation controller that the app entry point gets in there and it performs the isLoggedIn the same as the view controller class did, but it also has the same error.
Can someone walk me through how to fix it or any other better techniques? I felt like I am blind since I just get into the study of swift. Thank you!

Answer 1

You need to thread your request to perform the segue. Because your calling performSegue in the viewDidLoad() what happens is that your call is being called before everything is loaded, so you need to introduce some lag.
Threads are sometimes called lightweight processes because they have
their own stack but can access shared data. Because threads share the
same address space as the process and other threads within the
process, the operational cost of communication between the threads is
low, which is an advantage
An asynchronous function will await the execution of a promise, and an
asynchronous function will always return a promise. The promise
returned by an asynchronous function will resolve with whatever value
is returned by the function
Long story short, you need to wait for everything to be loaded into memory and if you're calling functions from the main stack/thread e.g. viewDidLoad() then there is a good chance that it hasn't been loaded into memory yet. Meaning, logInJump segue doesn't exist at that point in that view controller, thus your error.
The other possibility is you don't have the right view/segue ID but that should've thrown a different error.
Also, change the sender from nil to self. Actually this isn't necessary but I've always used self over nil
// change to desired number of seconds should be higher then 0
let when = DispatchTime.now() + 0.2
if isLoggedIn() {
DispatchQueue.main.asyncAfter(deadline: when) {
self.dismiss(animated: true, completion: nil)
self.performSegue(withIdentifier: "logInJump", sender: nil)
}
}