清除Swift中的可选变量

Question

If I declare an empty image:

var myImage: UIImage?

and then give it a value:

myImage = UIImage(named: "drawing.png")

how can I later remove that value, returning it to its original empty state?

Answer 1

var myImage: UIImage?

Is basically short hand for making a UIImage point to nil automatically.

So to reset it back to the original value say:

myImage = nil

Answer 2

将其值设置为nil，就像这样

myImage = nil

Answer 3

只需为它指定nil ：

myImage = nil

Answer 4

Optional is an enum type in Swift; it has two cases:

enum Optional<T> : NilLiteralConvertible {
    case None
    case Some(T)
    ...
}

By assigning an image to your Optional<UIImage> , you have implicitly specified .Some(image) . To clear it, you can use .None . But since Optional also conforms to NilLiteralConvertible , you can use the simpler and clearer nil .