key-value-observing

I noticed that there is no delegate to observe changes in UIDatePicker. Is there a way to detect when a change is made in the picker without confirming anything, like the moment it spins and lands on a new number I want to be able to detect that. I thought about key value observing, but I don't think there's a property that changes on the spot Go to IB and drag from the UIDatePicker to your .h file. Then select Handle this however you want in your .m file; XCode will add the method below for you. You need to add to your UIDatePicker the UIControlEventValueChanged event to handle date changes:

I have Parent entity with a custom class that has a transient and derived (read only) property called DerivedProperty . The value of DerivedProperty is dependent on the value of Parent.IndependentProperty1 and so whenever IndependentProperty1 changes, the value of DerivedProperty will change. However, Parent has a to-many relationship to Child (called children ) and DerivedProperty is also dependent on the value of IndependentProperty2 in all of Parent 's Child objects. So whenever IndependentProperty1 of Parent or IndependentProperty2 of any of the Child objects changes, I would like to

I'd like to monitor an NSCountedSet to see if its contents changes. Setting up KVO seems to compile but it's not being triggered. First question: can you observe a set? If so then is there something wrong with this message? [subViewA addObserver:subViewB forKeyPath:@"countedSet" options:0 context:NULL]; I'm really just trying to monitor the count of (number of objects in) the set if that helps. Edit - here's the observer (subViewB): - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context { if ([keyPath isEqual:@"countedSet"])

just wondering if this is possible in Swift 2.2, KVO on a computed property!? ie: var width = 0 var height = 0 private var area : Double { get { return with * height } } self.addOberser(self, forKeyPath: "area", ...... Would a client code modifying the with or height trigger observeValueForKeyPath? Just checking before engaging on a mayor class refactor. KVO's syntax being as annoying as it's is not worth even a playground if someone has an answer at hand (I am assuming answer is NO) regards! ~d That code won't work for two reasons: You must add the dynamic attribute to the area property, as

In line with Apple's own recommendations, when setting KVC/KVO compliant accessors manually, one should include BOTH KVO methods willChange and didChange . This is what I have done in all my manual accessor methods. However, observeValueForKeyPath:ofObject:change:context gets called for each half of the KVC methods (will and did) with exactly the same dictionary contents. When registering an observer using the option: NSKeyValueObservingOptionPrior the observer still gets called twice - once for each half - and, again, with identically the same dictionary contents, save only the difference

Here is my class: class ViewController: UIViewController { var myArray : NSArray! } I want to fire an event every time myArray points to a new array, like this: self.myArray = ["a"] self.myArray = ["b"] I've tried rx_observe but failed, here is my code: self.rx_observe(NSArray.self, "myArray").subscribeNext { (array) -> Void in print(array) } It only fires the first time, what's the problem? Most of the time, if you have control of the backing variable, you would prefer Variable to using rx_observe . class ViewController: UIViewController { var myArray : Variable<NSArray>! } The first time you