Re: Aggravation trying to implement NSValueTransformer subclasses in Swift
Re: Aggravation trying to implement NSValueTransformer subclasses in Swift
- Subject: Re: Aggravation trying to implement NSValueTransformer subclasses in Swift
- From: Quincey Morris <email@hidden>
- Date: Tue, 12 May 2015 22:38:18 +0000
On May 12, 2015, at 14:29 , William Squires <email@hidden> wrote:
>
> class IsNotEmptyTransformer : NSValueTransformer
> {
> }
>
> but the example in the documentation is in ObjC, not Swift, and refers to id, not to "Bool"s or "String"s. Hints, anyone?
Using a value transformer at all seems like a poor choice, and using one in Swift seems even less desirable.
If you are intent on using one, you’ll need to ask a more specific question. What ‘id’ are you referring to? If you’re talking about the transformed value, then you have to use an object — specifically NSNumber to represent a boolean value. IOW, for your use case, the transformer would transform between NSNumber and NSString.
Surely it would be far easier, though, to do what you would do in a modern Obj-C app: use a derived property. Add a new property to the window controller:
class MyWindowController : NSWindowController
{
dynamic var message: String
dynamic var messageIsEmpty: Bool {return String == “”}
and bind the button’s Enabled binding to the “messageIsEmpty” property. That’s not quite all, though, because as it stands, “messageIsEmpty” isn’t KVO-compliant, so you also need to add:
static var keyPathsForValuesAffectingMessageIsEmpty: NSSet {return NSSet (object: "messageIsEmpty”)}
(All code written in Mail, not tested.)
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