在Swift中读取CGPoints的NSArray

Question

I have a function in an Objective-C class that returns an NSArray:

- (NSArray *) myAwesomeFunction {
   // Good stuff here
   return array
}

Now I know that the members of this array are all NSValue objects with a CGPoint inside. This information is not available to Swift however, which infers the return type (correctly) as [AnyObject]!

Now when I try to cast the members of the array into an NSValue I get a cast error as I should.

let myArray = AnObjectiveCClass.myAwesomeFunction()
let myValue = myArray[0] as NSValue // Cast error since AnyObject cannot be cast to NSValue

This leaves me with a problem though, how can I access the contents of the array in my Swift class? In the end I want to retrieve the CGPoint values inside of the array.

Answer 1

In my opinion, you can cast the the whole array to a [NSValue] array:

if let downcastNSValueArray = myArray as? [NSValue] {
    let myValue = downcastNSValueArray[0]
}

Answer 2

You can simply add an Objective-C generics annotation to your method:

+ (NSArray<NSValue *> *) myAwesomeMethod {
   // Good stuff here
   return array;
}

Now Swift automatically infers the type:

let myArray = MyClass.myAwesomeMethod()
let myValue = myArray[0]
let myPoint = myValue.pointValue

Note that myArray will be an implicitly-unwrapped optional ie an [NSValue]! , so you could also add nullability annotations if you know myAwesomeMethod won't ever return nil . myValue will be considered non-optional. So the code above doesn't need any additional type handling to satisfy the compiler, but may still trigger runtime exceptions if myArray == nil or if myArray.count < 1 .