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iOS Swift Closures Functions as First Class Citizens Functions as Parameters

Michael Southon
Michael Southon
1,951 Points
Posted by Michael Southon
Michael Southon
1,951 Points

fatal error: unexpectedly found nil while unwrapping an Optional value

Hi,

I have a Storyboard with two labels (called firstSelectedDate and secondSelectedDate) and two buttons (called firstDate and secondDate) plus a UIDatePicker.

The two buttons send start and end dates from the UIDatePicker to the two labels. I also have an IB Action button (called calculateDays), which when pressed will calculate the difference between the end date and the start date and send the output to a label (called resultNumberOfDays).

But I've run into a problem: the calculateDays function is crashing with the error message: "fatal error: unexpectedly found nil while unwrapping an Optional value". I've searched up this error message and I understand I must safely unwrap one of my constants using the 'if let' statement, but I'm lost as to how to do that.

If anyone can help I will be sooo grateful. Thanks!

==============

@IBAction func calculateDays(sender: AnyObject) {

    let start = String(firstSelectedDate.text!)
    let end = String(secondSelectedDate.text!)

    let dateFormatter = NSDateFormatter()
    dateFormatter.dateFormat = "yyyy-MM-dd"

    if let startDate:NSDate = dateFormatter.dateFromString.(start)!

        // fatal error: unexpectedly found nil while unwrapping an Optional value

    let endDate:NSDate = dateFormatter.dateFromString(end)! //
    let cal = NSCalendar.currentCalendar()


    let unit:NSCalendarUnit = NSCalendarUnit.NSDayCalendarUnit

    let components = cal.components(unit, fromDate: startDate, toDate: endDate, options: []) // error: Use of unresolved identifier 'startDate'


    print(components)

}