> On Apr 17, 2017, at 3:24 AM, Rick Mann <rm...@latencyzero.com> wrote:
>
> I have a number of properties in Objective-C written like this,
> short-circuiting notifications when the value doesn't change:
>
> -------------
> @synthesize version = mVersion
>
> - (void)
> setVersion: (NSString *) inVersion
> {
> if (inVersion == nil && mVersion == nil)
> {
> return;
> }
> if ([inVersion isEqualToString: mVersion])
> {
> return;
> }
>
> [self willChangeValueForKey: @"version"];
> mVersion = inVersion;
> [self didChangeValueForKey: @"version"];
> }
> -------------
>
> Now I want to translate this method into Swift. Thing is, AFAIK you can't
> name the ivar created for a property. Is there a way to translate this to
> swift?
I’ve been converting a lot of KVO properties to Swift lately. Here’s how I’d do
this:
// Only needed if the property will be accessed by Objective-C code, since
Swift code won’t see the swizzled accessors anyway for a non-dynamic property.
// @objc annotation is needed on every method we write here, since otherwise
it’ll quit working when @objc inference is removed in Swift 4 (SE-0160)
@objc private static let automaticallyNotifiesObserversOfVersion: Bool = false
// Our actual version property. If you want, you can create a private property
named “mVersion” and it will function like an instance variable.
// But I’d probably just use willSet and didSet.
// Note that this doesn’t need to be dynamic, since we are not relying on
Cocoa’s built-in automatic swizzling,
// which is only needed if we are not calling willChangeValue(forKey:) and
didChangeValue(forKey:) ourselves.
@objc var version: String {
willSet {
// Send the willChange notification, if the value is different from its
old value.
if newValue != self.version {
self.willChangeValue(forKey: #keyPath(version))
}
}
didSet {
// Send the didChange notification, if the value is different from its
old value.
if oldValue != self.version {
self.didChangeValue(forKey: #keyPath(version))
}
}
}
Charles
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