Default value won't set to Nil? - Swift

You can't pass nil to a function parameter unless that parameter is an Optional. You need to rewrite your function to accept an optional:

func stockInfoPerDay(jsonData: StockInfo?) { guard let jsonData = jsonData else { return } //Exit if you are passed a nil. CropPriceView.pricesForOneMonth.removeAll() //Move this above the guard if you want to empty the CropPriceView when you are passed a nil. for data in jsonData.data{ CropPriceView.pricesForOneMonth.append(CGFloat(data.close)) } } 

Note that another way you could handle this is to leave your stockInfoPerDay() function alone, and use "optional binding" (if let) to only call your function if the parameter is not nil:

.onAppear(){ if let validJsonData = jsonData { stockInfoPerDay(jsonData: validJsonData) } if let validSingleJSONData = jsonData { stockInfoSingleDay(singleJSONData: validSingleJSONData) } } 

You need to ideally set it up so that your functions accept optionals as parameters and handle the nil case in the functions, often with a guard statement. However, since you said you had an problem with that and I don't know what that problem is, I can just suggest changing your code to something like this

stockInfoPerDay(jsonData: jsonData ?? StockInfo()) // <- Just make sure you have a good default initializer for the StockInfo object. Handle the possibility that jsonData was nil and StockInfo is empty inside the stockInfoPerDay function. stockInfoSingleDay(singleJSONData: singleJSONData ?? StockInfoOneDay()) 

Let me know if I this helps.