Re: Key-Value-Observing and Collections
Re: Key-Value-Observing and Collections
- Subject: Re: Key-Value-Observing and Collections
- From: Mike Abdullah <email@hidden>
- Date: Thu, 25 Oct 2007 16:03:53 +0100
You can't. An NSMutableArray is a self-contained object for storing an
array. The documentation on it explicitly states that -
addObsever:forKey is not supported by it for this reason. You must
observe it through the use of appropriate accessor methods on another
object (as in the example below). That is why it is "key" value
observing.
Mike.
P.S. I should point out that you don't have to implement all of the
methods below. This would suffice:
- (NSArray *)grades
- (void)insertObjectInGrades:(id)grade atIndex:(unsigned int)index
- (void)removeObjectFromGradesAtIndex:(unsigned int)index
On 25 Oct 2007, at 15:21, Philip Mötteli wrote:
Am 25.10.2007 um 15:51 schrieb David Spooner:
You can expose 'grades' as a to-many property by adding the
following methods to Pupil
- (unsigned int) countOfGrades
- (id) objectInGradesAtIndex:(unsigned int)index
- (void) insertObjectInGrades:(id)grade atIndex:(unsigned int)index
- (void) removeObjectFromGradesAtIndex:(unsigned int)index
- (void) replaceObjectInGradesAtIndex:(unsigned int)index
withObject:(id)grade
Implement these to manipulate your instance variable (which you
must rename to something other than grades).
Now all methods of NSMutableArray are applicable to your grades
property and will automatically generate
the appropriate key/value observations. For example
NSMutableArray *myGrades = [me mutableArrayValueForKey:@"grades"];
[myGrades removeObject:badGrade];
[myGrades addObject:goodGrade];
You might add the following method for aesthetics...
- (NSMutableArray *) mutableGrades
{ return [self mutableArrayValueForKey:@"grades"]; }
Thanks for these really interesting points!
What would you do, if you just want to be notified, when an object
has been added or removed from some NSMutableArray?
Thanks
Phil
On 25-Oct-07, at 7:23 AM, Philip Mötteli wrote:
There is something, I just don't get with KVO. Lets say, I have an
object
@interface Pupil
{
NSMutableArray grades;
}
- (void)setGrades:(NSMutableArray *)theGrades;
- (NSMutableArray *)grades;
- (void)addGrade:(Grade *)aGrade;
@end
Using KVO, I want to be notified not only, when the old grades
collection object (NSMutableArray) is replaced, but also, when a
Grade instance is added to the grades collection (something like
"[grades addObject:aGrade]").
The first case is easy, because I know the attribute name
(grades), which gives the key. But for the second, I don't know
the attribute name, so I can't add an observer.
Can anybody explain me how to do this?
Thanks
Phil
_______________________________________________
Cocoa-dev mailing list (email@hidden)
Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden
_______________________________________________
Cocoa-dev mailing list (email@hidden)
Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden