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
• Delivered-to: email@hidden
• Delivered-to: email@hidden

Mike.

- (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

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