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Questions tagged [key-value-coding]

Key Value Coding is a mechanism for accessing an object’s properties indirectly, using strings to identify properties, rather than through invocation of an accessor method or accessing them directly through instance variables.

390 questions
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6 answers

Difference between objectForKey and valueForKey?

What is the difference between objectForKey and valueForKey? I looked both up in the documentation and they seemed the same to me.
Devoted
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7 answers

Observing an NSMutableArray for insertion/removal

A class has a property (and instance var) of type NSMutableArray with synthesized accessors (via @property). If you observe this array using: [myObj addObserver:self forKeyPath:@"theArray" options:0 context:NULL]; And then insert an object in the…
Adam Ernst
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6 answers

Getting string from Swift 4 new key path syntax?

How can you get a string value from Swift 4 smart keypaths syntax (e.g., \Foo.bar)? At this point I'm curious about any way at all, does not matter if it's complicated. I like the idea of type information being associated with smart key path. But…
Dannie P
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4 answers

How do you tell if a key exists for an object using Key-Value Coding?

I'd like to test whether an object has a writeable @property in the iPhone SDK. One possible way of doing this is to check the -valueForKey: method, but that seems rather inelegant! Example: @try { id *value = [instance…
Ted
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3 answers

What is the right choice between NSDecimal, NSDecimalNumber, CFNumber?

I've read a lot about NSDecimal, NSNumber, NSNumberDecimal, CFNumber... and it begins to be a kind of jungle to me. Basically, I'm trying to create a simple model class that will handle simple computations, like this one: #import…
charlax
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26
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2 answers

Using setValue(value, forKey: key) on Int? types fires non key value coding-compliant method

I'm successfully using the setValue(value, forKey: key) method in my NSKeyValueCoding compliant Swift NSObject subclass. This works perfectly well on String optionals, e.g. var name:String? However, on Int optionals, it fails, triggering the…
Max MacLeod
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3 answers

Directly accessing nested dictionary values in Objective-C

Is there a way to directly access an inner-array of an an outer array in Objective-C? For example, a call to an external data source returns the following object: { bio = "this is the profile.bio data"; "first_name" = John; "last_name" =…
user455889
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2 answers

Access Objective-C property dynamically using the name of the property

I know the string name of a property of an object. How would I go about getting and setting that property using the string?
quano
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1 answer

How can I get all values for specific key from each NSDictionary in an NSArray?

I have an array which contains dictionary objects. In each dictionary the key are common. Now I want to get all the values of that key. I have got these values with iteration, but I am looking for some straight forward way or a default method which…
hgpl
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5 answers

Getting array elements with valueForKeyPath

Is there any way to access an NSArray element with valueForKeyPath? Google's reverse geocoder service, for example, returns a very complex data structure. If I want to get the city, right now I have to break it into two calls, like…
jsd
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20
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1 answer

How does NSValue do its magic?

I have an MVC application. The model has a property that is a struct NSSize. It is writable like this: - (void)setSize:(NSSize)aSize; The view sets this NSSize using key-value-coding. However, you can not key-value-code a struct, so I wrapped it in…
bastibe
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8 answers

iPhone app crashing with NSUnknownKeyException setValue:forUndefinedKey:

I'm writing my first iPhone app, so I haven't gotten around to figuring out much in the way of debugging. Essentially my app displays an image and when touched plays a short sound. When compiling and building the project in XCode, everything builds…
btw
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5 answers

Using valueForKeyPath on NSDictionary if a key starts the @ symbol?

I want to use valueForKeyPath on my NSDictionary, but the problem is that one of the keys is a string that starts with the @ symbol. I have no control over the naming of the key. I'm having problems trying to create the key path as I'm getting a…
Michael Waterfall
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1 answer

What is the KVC Search Pattern for mutableArrayValueForKey?

I'm attempting to understand Cocoa's Key-Value Coding (KVC) mechanism a little better. I've read Apple's Key-Value Programming Guide but am still a little confused about how certain KVC methods search for keys. Particularly,…
Dave
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2 answers

Defining your own key path operators in cocoa

Is it possible to define your own key path operators, such as @avg, @sum, etc…
cfischer
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