Swift how to wait until a value changes - ios

Question

I am writing an application which tests your ability in Classical Greek. And I have a few View Controllers. In the test view controller, I have a huge Begin button, which when pressed initiates a sequence of code, as follows:
#IBAction func test(_ sender: Any) {
beginBtn.isHidden = true
beginBtn.isEnabled = false
answerOne.isHidden = false
answerTwo.isHidden = false
answerThree.isHidden = false
answerFour.isHidden = false
data.currentNumOQue = (data.qCQ + data.qWQ + data.qSQ)
if data.chooseCAlertDataLoaded == false {
data.chooseCharacterQuestionType.addAction(data.chooseCharacterQuestionTypeEngGrk)
data.chooseCharacterQuestionType.addAction(data.chooseCharacterQuestionTypeGrkEng)
data.chooseCAlertDataLoaded = true
} else {
print("not first question")
}
while data.currentQC <= data.qCQ {
present(data.chooseCharacterQuestionType, animated: false, completion: nil)
DispatchQueue.global(qos: .background).async {
while data.chooseCAlertReturnsEngGrk == nil {
}
DispatchQueue.main.sync {
if data.chooseCAlertReturnsEngGrk == true {
//Eng-Grk QUestion
data.chooseCAlertReturnsEngGrk = nil
} else {
//Grk=Eng QUestion
data.chooseCAlertReturnsEngGrk = nil
}
}
}
data.currentQC += 1
data.currentQ += 1
}
data.currentQC = 1
data.currentQW = 1
data.currentQS = 1
}
Can anyone help me in how to wait until the value chooseCAlertReturnsEngGrk is not nil and execute on, but not 'freezing' the UI when doing so?

Answer 1

Override didSet to call some function.. then in that callback function, do whatever you want with the parameter..
class DataSomething {
var chooseCAlertReturnsEngGrkObserver: ((_ newValue: SomeTime?) -> Void)?
var chooseCAlertReturnsEngGrk: SomeType? = nil {
didSet {
chooseCAlertReturnsEngGrkObserver?(chooseCAlertReturnsEngGrk)
}
}
}