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iOS Build a Weather App with Swift (Retired) Displaying Our Weather Data Handling Failures

Nicolo Figiani
Nicolo Figiani
4,012 Points
Posted by Nicolo Figiani
Nicolo Figiani
4,012 Points

where do things like ".Default" come from?

in this video, parameters are used the following initialisers:

UIAlertAction(title: "Ok", style: .Default, handler: nil)

UIAlertAction(title: "Cancel", style: .Cancel, handler: nil)

I know they are defined as "UIAlertActionStyle" but in the documentation nothing more is explained.

Can someone explain more in details where the dot notation of parameters ".Default" and ".Cancel" come from? What are actually these parameters and how they work?

Thanks a lot, bye!

2 Answers

Stone Preston
Stone Preston
42,016 Points
Stone Preston
Stone Preston
42,016 Points

the AlertActionStyle enum is defined here

as you can see, it has 3 values. Default, Cancel, and Destructive.

enumeration values can be accessed using

EnumerationName.Value

so you could access the Cancel value of the UIAlertActionStyle enumeration like so:

UIAlertAction(title: "Cancel", style: UIAlertActionStyle.Cancel, handler: nil)

however, in the UIAlertAction() initializer, Swift infers the type of the style argument to be that of UIAlertActionStyle, so you can drop the name of the enum, and just use .Cancel 

//swift knows that style is going to be of type UIAlertActionStyle, so you dont need to provide that before the .
UIAlertAction(title: "Cancel", style: .Cancel, handler: nil)

it infers the type from the definition of the initializer here:

convenience init(title title: String,
           style style: UIAlertActionStyle,
         handler handler: ((UIAlertAction!) -> Void)!)

you can see that the type of the style parameter is indeed UIAlertActionStyle, which is why you can drop the enum name before the dot

Nicolo Figiani
Nicolo Figiani
4,012 Points
Nicolo Figiani
Nicolo Figiani
4,012 Points

Thanks a lot for the answer, so accurate and straight to the point!