How can stop to jump next view controller? (swift) - ios

Question

I am using segue to send data from one viewController to destinationViewController. I set button and use push segue to connects to next view controller. In the first view, I set a boolean to check the images is or not empty. If there is any empty, it will pop up alert to remind users. If success, it will send the images to next view controller.
Although I can transmit the images and pop up the alert, it also jump to next view controller if there is any empty. Moreover, the alert is popped after jumping to next view controller, not in the first view controller
Now, here is the code
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if Jumpsuit.isHidden == false && self.Hair.image != nil && self.Jumpsuit.image != nil && self.Shoes.image != nil {
let DestViewController : ChooseBGViewController = segue.destination as! ChooseBGViewController
DestViewController.imgHair = Hair.image
DestViewController.imgJumpsuit = Jumpsuit.image
DestViewController.imgShoes = Shoes.image
DestViewController.dressingtype = 1
} else if Jumpsuit.isHidden == false && self.Hair.image == nil || self.Jumpsuit.image == nil || self.Shoes.image == nil {
let alert = UIAlertView()
alert.title = "No Image"
alert.message = "Please check again"
alert.addButton(withTitle: "OK")
alert.show()
}
}
How can I stop jumping to next view controller and pop up the alert in first view controller. Please help!

Answer 1

You can use shouldPerformSegue(withIdentifier:sender:) for that and return Bool value according your condtion.
override func shouldPerformSegue(withIdentifier identifier: String, sender: Any?) -> Bool {
if Jumpsuit.isHidden == false && self.Hair.image == nil || self.Jumpsuit.image == nil || self.Shoes.image == nil {
//Show UIAlertController instead of UIAlertView it is deprecated
return false
}
return true
}

Answer 2

When the user tapped the button you would use the IBAction that will first check what you need (the image..) and then you could use 2 approaches:
You can now use performSegue which will trigger the known prepareForSegue and use the segue you created
You can use the instantiateViewController(withIdentifier: approach as follows (and don't forget to disconnect the segue):
let nextVC = storyboard?.instantiateViewController(withIdentifier: "YourViewControllerID")
self.present(nextVC!, animated: true, completion: nil)
or if you have navigation controller:
self.navigationController?.pushViewController(nextVC!, animated: true)