How do I get a value as a Swift type from an object of type Unmanaged<AnyObject>
. My example is using an ABRecordRef
I'm creating a contact object to manage once I get the ABRecordRef
, but I'm having trouble translating from ObjC. Here's what I have:
init(recordRef: ABRecordRef) {
if let firstName = ABRecordCopyValue(recordRef, kABPersonFirstNameProperty) {
self.firstName = firstName
}
}
If it were ObjC, I would do:
CFTypeRef firstNameRef = ABRecordCopyValue(recordRef, kABPersonFirstNameProperty);
if (firstNameRef) {
self.firstName = (__bridge NSString *)firstNameRef;
}
I can't seem to find the right combination of downcasting / conversion, so any help is appreciated.
Since NoOne answered before I solved it, I'll add the answer here:
firstName.takeRetainedValue() as? String
If you look at the header of the Unmanaged
struct type, you'll find this:
/// Get the value of this unmanaged reference as a managed
/// reference and consume an unbalanced retain of it.
///
/// This is useful when a function returns an unmanaged reference
/// and you know that you're responsible for releasing the result.
func takeRetainedValue() -> T
So, because the CFTypeRef
is converted to Unmanaged<AnyObject>
in Swift.
Unmanaged
uses generics to define a return type, and it is declared like so:
Unmanaged<T>
Our object is of type Unmanaged<AnyObject>
which means that takeRetainedValue()
will return type T
, or in our case, type AnyObject
. I use optional downcasting since my property firstName
is of type String?
.
You can use the takeRetainedValue
method to get your value out of your Unmanaged
object. In Foundation API's, I'm guessing that they will mostly be of type Unmanaged<AnyObject>!
and a downcast will be required. The generic formula appears to be:
var unmanagedObject: Unmanaged<AnyObject> = someFunctionThatReturnsAnUnmanagedObject()
var newValue: Type = unmanagedObject.takeRetainedValue as Type