key-value-observing

问题 Ok, I initially wanted to make NSSortDescriptor of a request for NSFetchedResultsController to sort based on the property in my NSManagedObject subclass, but It obviously won't do it, because NSFetchedResultsController is limited to predicates and sort descriptors that work on the fetched entity and its relations, so I decided to create a transient attribute in my data model, synthesis the property for this attribute to ivar in my NSManagedObject subclass, and sort based on it. When running

问题 I can't find in the Docs where they explain all those fields and what they mean. Especially "Controller Key" is not clear to me. 回答1: The Controller Key pop-up menu is a way to help you discover what keys the controller (typically a NSArrayController, NSObjectController or a NSTreeController) presents. The best example is the selection key of NSArrayControllers, which contains the set of selected objects. What is confusing is the NSObjectController presents a 'selection' key too, although the

问题 Im trying to find a good way to handle memcache keys for storing, retrieving and updating data to/from the cache layer in a more civilized way. Found this pattern, which looks great, but how do I turn it into a functional part of a PHP application? The Identity Map pattern: http://martinfowler.com/eaaCatalog/identityMap.html Thanks! Update: I have been told about the modified memcache (memcache-tag) that apparently does do a lot of this, but I can't install linux software on my windows

问题 I am hitting the below error after I added 2 additional fields to my core data model. CarPark_CarPark_ was deallocated while key value observers were still registered with it. Observation info was leaked, and may even become mistakenly attached to some other object. Set a breakpoint on NSKVODeallocateBreak to stop here in the debugger. Here's the current observation info: <NSKeyValueObservationInfo 0x1b6510> ( <NSKeyValueObservance 0x19b210: Observer: 0x1a8cf0, Key path: coordinate, Options:

问题 Why this code works fine: NSArray* arr = @[[CALayer layer], [CALayer layer]]; NSString *sumKeyPath = @"@sum.bounds.size.width"; CGFloat totalSize = [[arr valueForKeyPath:sumKeyPath] floatValue]; But this code give error: NSArray* arr = @[[UIImage imageNamed:@"img1"], [UIImage imageNamed:@"img2"]]; NSString *sumKeyPath = @"@sum.size.width"; CGFloat totalSize = [[arr valueForKeyPath:sumKeyPath] floatValue]; Error : [NSConcreteValue valueForUndefinedKey:]: this class is not key value coding

问题 I have an unordered array with instances of the following class: @interface Place : NSObject { } @property (nonatomic, copy) NSString *country; @property (nonatomic, copy) NSString *city; @property (nonatomic, retain) NSURL *imageURL; -(id) initWithCountry: (NSString *) aCountry city: (NSString *) aCity imageUrl: (NSURL *) aUrl; @end and I'm trying to sort it with sortedArrayUsingDescriptors by country and city. The docs for NSSortDescriptor say that the arg of initWithKey: is a Key Path.

问题 Put simply, is there a way to receive a general notification when any property in an Objective-C class is changed? I know I can use KVO to monitor particular property changes, but I have the need to call a particular method whenever any setProperty: message is sent to my class. I want to be able to receive a generic notification without any concern about which property in particular was modified. If it helps to clarify why I want to do this, I am making use of some fast table scrolling code

问题 I want to watch for changes in a UIView 's frame , bounds or center property. How can I use Key-Value Observing to achieve this? 回答1: There are usually notifications or other observable events where KVO isn't supported. Even though the docs says 'no' , it is ostensibly safe to observe the CALayer backing the UIView. Observing the CALayer works in practice because of its extensive use of KVO and proper accessors (instead of ivar manipulation). It's not guaranteed to work going forward. Anyway,

问题 I want to watch for changes in a UIView 's frame , bounds or center property. How can I use Key-Value Observing to achieve this? 回答1: There are usually notifications or other observable events where KVO isn't supported. Even though the docs says 'no' , it is ostensibly safe to observe the CALayer backing the UIView. Observing the CALayer works in practice because of its extensive use of KVO and proper accessors (instead of ivar manipulation). It's not guaranteed to work going forward. Anyway,

问题 Being new to objective-c, cocoa, and iPhone dev in general, I have a strong desire to get the most out of the language and the frameworks. One of the resources I'm using is Stanford's CS193P class notes that they have left on the web. It includes lecture notes, assignments and sample code, and since the course was given by Apple dev's, I definitely consider it to be "from the horse's mouth". Class Website: http://www.stanford.edu/class/cs193p/cgi-bin/index.php Lecture 08 is related to an