将ivar传递给Swift方法

Question

I am making a simple reminder app in Swift and I'm having a hard time figuring out why I can't get my method to compile.

 for reminder in self.reminders {

            if dates.contains(dateFormatter.stringFromDate(reminder.date)) {
                dates.add(reminderDate)
            }

}

On the call to stringFromDate I am getting an error saying

"Cannot invoke "stringFromDate" with an argument list of type (NSDate?!)"

The date ivar is an NSDate, what do I need to be able to call it?

I declare the property as var date: NSDate

Declaration for the property var reminders = []

class TRReminder {

        enum TRPriority {
            case Low, Medium, High
        }

        var title: String
        var date: NSDate
        var location: String
        var priority: TRPriority
        var note: String


        init(title: String, date: NSDate, location: String, priority: TRPriority, note: String) {

            self.title = title
            self.date = date
            self.location = location
            self.priority = priority
            self.note = note

        }

    }

Answer 1

Do this

var reminders = [TRReminder]()

Declaring it as [] is, I believe, equivalent to [AnyObject?]

Answer 2

Sometimes it's best to break up the method a bit more to see where any potential loop holes are here, try replacing your implementation with this on run through the output to see if you're missing anything:

for reminder in self.reminders {
    println("\(reminder)") //sanity check
    if let date = reminder.date {
        if let formattedDate = dateFormatter.stringFromDate(date) {
            if dates.contains(formattedDate) { 
                dates.add(reminderDate) //the logic here seems a bit confusing? where does reminderDate come from?
            }
        } else {
            println("oops") //yet another sanity check
        }
    } else {
        println("something went wrong here") // another sanity check
    }
}

This will surely not fix your problem but it might help you get on track to see where a mistake was made.

Hope this helps!