How to represent an optional Bool (Bool?) in Objective-C? - swift

Question

I am trying to write a protocol in swift
#objc protocol RestAPIManagerDelegate {
optional func credentialValidated(isValid: Bool?)
}
But I am getting following error:
'Method cannot be marked #objc because the type of the parameter cannot be represented in Objective-C'
Any suggestion?

Answer 1

The problem is this type declaration:
`isValid: Bool?`
That is perfectly fine in Swift. But you cannot expose it to Objective-C, because Objective-C does not have any notion of an Optional BOOL - a BOOL in Objective-C is basically just a number, a primitive C datatype (what we call a scalar).
Here's another way of looking at it. In an interchange with Objective-C, you can use a Swift Optional anywhere that Objective-C can say nil - indeed, to a large extent Swift Optional exists exactly in order to deal with the possibility that Objective-C will say nil or that you might need to say nil to Objective-C. But a BOOL in Objective-C can never be nil - it can only be YES or NO (Swift true or false).
So you have three choices:
Take away the #objc that exposes all this to Objective-C
Remove the Optional and just declare that type a Bool
Use an object type. For example, declare the type as AnyObject? (or NSNumber?). This will work because Swift will bridge a Bool to an NSNumber (including as it passes into an AnyObject), and Objective-C will deal just fine with an Optional AnyObject or Optional NSNumber because those are object types, not scalars.

Answer 2

Object-C does not have the concept of optionals, try to remove the "?" from your declaration

Answer 3

It's OK to use NSNumber? instead, but there is another way.
You can create OptionalBool enum and use it instead of Bool? for compatibility with Objective-C.
Creating OptionalBool enum in Swift code:
#objc enum OptionalBool: Int {
case none
case yes
case no
}
#objc protocol RestAPIManagerDelegate {
#objc optional func credentialValidated(isValid: OptionalBool)
}
Using OptionalBool in Objective-C code:
#interface RestAPIManagerHandler () <RestAPIManagerDelegate>
#end
#implementation RestAPIManagerHandler
- (void)credentialValidatedWithIsValid:(enum OptionalBool)isValid {
switch (isValid) {
case OptionalBoolYes:
NSLog(#"TRUE");
break;
case OptionalBoolNo:
NSLog(#"FALSE");
break;
case OptionalBoolNone:
NSLog(#"NULL");
break;
}
}
#end

Answer 4

Swift Bool are converted in NSNumber so for example if a Swift method returns [Bool] and if you receive this array in Objective-C code, it become a NSArray <NSNumber *>. And if you give this array to a Swift method which receives a [Bool] as parameter, the conversion will be done automatically.

Answer 5

If you are wanting to just do a protocol in Swift, for use within Swift, without optionals you can do this:
public protocol Note {
var content: [ContentType] {get}
func insertNote(note: Note) -> Bool
}
That will force a class to implement a method that returns a Bool and have an array of some class called ContentType.
If you want to make the method optional, you must specify the objc keyword as you have done, regardless if you are interoperating with Objective-C or not. At that point, everything else should work in your example.
#objc protocol RestAPIManagerDelegate {
optional func credentialValidated(isValid: Bool?)
}
From Apples documentation:
Optional protocol requirements can only be specified if your protocol is marked with the #objc attribute.
This attribute indicates that the protocol should be exposed to Objective-C code and is described in Using Swift with Cocoa and Objective-C. Even if you are not interoperating with Objective-C, you need to mark your protocols with the #objc attribute if you want to specify optional requirements.
Note also that #objc protocols can be adopted only by classes, and not by structures or enumerations. If you mark your protocol as #objc in order to specify optional requirements, you will only be able to apply that protocol to class types.
The example given by Apple:
#objc protocol CounterDataSource {
optional func incrementForCount(count: Int) -> Int
optional var fixedIncrement: Int { get }
}