SWIFT-防止同时调用同一函数

Question

I have an application where the main UI waits for some calculation to be done before updating. The whole application depends solely on the user's connectivity to wifi as we are making any api calls to calculate the data. Sometimes, in RARE conditions, the function that runs everything gets executed twice... causing the updated UI to display invalid data.

What are some ways i can prevent this from happening. Sorry i'm not showing code because it'll be easier to explain the concept.

Edit: To reproduce this error, this is what i do. Pseudocode below

override func viewDidLoad() {
    mainCall()
}


override func viewWillAppear(_ animated: Bool) {
    mainCall()
}


func executeOne(){
    callA(){}
    callB(){}
    etc...
}

Answer 1

You can use a bool variable to indicate whether an API call is already in progress or not and only trigger an API call in case another one is not in progress.

class YourClass {
    var apiCallIsInProgress = false

    func apiCall(){
        if !apiCallIsInProgress {
            // doApiCall is the function actually implementing the API call and returning the result through a completion handler
            doApiCall(completion: {
                apiCallIsInProgress = false
            }
        } else {
            apiCallIsInProgress = true
        }
    }
}