Performing Segue with Prepare after validation check - ios

Question

I have a form that needs to be validated before performing a segue and also sending over the data to the next view controller. For now I'm just checking to see if all text fields are filled in:
#IBAction func startBtn(_ sender: Any) {
if(idInput.text == "" || dob1Field.text == "" || dob2Field.text == "" || dob3Field.text == ""){
print("no text")
}
}
My idea is, when the start button is pressed, check if all fields are filled, if they are use prepare to segue to the next VC and send the data.
I'm struggling to understand how to do this, I linked the start button on the storyboard to the VC and gave it an identifier mainUse since it is going to the mainUseController
Here is the prepare function:
override func prepare(for segue: UIStoryboardSegue, sender: Any?){
if segue.identifier == "mainUse"{
let vc = segue.destination as! mainUseController
}
}
The part I'm struggling to understand is how to call the prepare function once the check is done and succeeded. Thanks.

Answer 1

I linked the start button on the storyboard to the VC and gave it an
identifier mainUse since it is going to the mainUseController
Well here is the issue: your segue seems to be generated by dragging from the button to the destination view controller, don't do this because the segue will performed regardless of what's implemented in the button action. Instead drag from the view controller itself (but not from the button) to the destination view controller:
control + drag from the view controller to the destination controller
At this point, tapping the button won't forcibly navigates you to the destination view controller. Next what you should do is to perform the segue if the conditions are met, by calling performSegue(withIdentifier:sender:) method:
#IBAction func startBtn(_ sender: Any) {
if idInput.text == "" || dob1Field.text == "" || dob2Field.text == "" || dob3Field.text == "" {
print("no text")
return
}
// just don't forget to assign the segue identifier as 'mainUse'...
performSegue(withIdentifier: "mainUse", sender: nil)
}

Answer 2

Use the following code to perform the segue, first check if all condition fulfill then fire segue else display error message accordingly.
#IBAction func startBtn(_ sender: Any) {
if(idInput.text == "" || dob1Field.text == "" || dob2Field.text == "" || dob3Field.text == ""){
print("no text")
//Show alert message here
}else{
self.performSegue(withIdentifier: "mainUse", sender: self)
}
}

Answer 3

prepare(for segue:) method is called by the ViewController delegate, you should avoid putting code there that you need to trigger.
What you can call for segueing is performSegue(withIdentifier:sender:)
More in:
https://developer.apple.com/documentation/uikit/uiviewcontroller/1621413-performsegue
IMPORTANT CAVEAT
Remember that your outlets are nil when segueing, if you want to assign or pass data to the receiver VC, create a strong property and assign that value before you segue but after the VC instantiation. Labels, texts, etc won't receive any data until they're draw.
If you need the entries from the text fields to be sent over to the next view controller, create a placeholder property and assign it during the segueing process.
You have a nice day!

Answer 4

#IBAction func startBtn(_ sender: Any) {
if idInput.text?.isEmpty ?? true || dob1Field.text?.isEmpty ?? true || dob2Field.text?.isEmpty ?? true || dob3Fieldtext?.isEmpty ?? true { print("some textField is empty") return }
dispatch_async(dispatch_get_main_queue()) { [unowned self] in
self.performSegueWithIdentifier("YourIdentifier", sender: self)
}
}
If you are using navigation controller:
#IBAction func startBtn(_ sender: Any) {
if idInput.text?.isEmpty ?? true || dob1Field.text?.isEmpty ?? true || dob2Field.text?.isEmpty ?? true || dob3Fieldtext?.isEmpty ?? true { print("some textField is empty") return }
if let viewController = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "YourIdentifier") as? NextViewController{
if let navigator = navigationController {
navigator.pushViewController(viewController, animated: true)
}
}
}