I need to create a series of classes that implement the Singleton
design pattern. These classes have a lot of similar methods (I am
trying to create a series of DAOs see: http://en.wikipedia.org/wiki/Data_Access_Object)
.
I was thinking that it would be best to create a super class, and a
series of subclasses to that super class. The problem I am running
upon is that the Singleton pattern requires a static variable.
How can I get a variable that is static to each subclass, but that is
declared in the super class?
for example I tried this.
/*-------------------------------------------------------------
#import <Cocoa/Cocoa.h>
@interface SuperClass : NSObject {
}
- (void) addToMyVar;
- (int) getMyVar;
@end
@implementation SuperClass
static int MyVar = 0;
- (void) addToMyVar {
++MyVar;
}
- (int) getMyVar {
return MyVar;
}
@end
@interface SubClass1 : SuperClass {
}
@end
@implementation SubClass1
@end
@interface SubClass2 : SuperClass {
}
@end
@implementation SubClass2
@end
int main(int argc, char *argv[])
{
SubClass1 *mySubClass1 = [[SubClass1 alloc] init];
SubClass2 *mySubClass2 = [[SubClass2 alloc] init];
NSLog(@"1 before = %i", [mySubClass1 getMyVar]);
NSLog(@"2 before = %i", [mySubClass2 getMyVar]);
[mySubClass1 addToMyVar];
NSLog(@"1 after 1 = %i", [mySubClass1 getMyVar]);
NSLog(@"2 after 1 = %i", [mySubClass2 getMyVar]);
[mySubClass2 addToMyVar];
NSLog(@"1 after 2 = %i", [mySubClass1 getMyVar]);
NSLog(@"2 after 2 = %i", [mySubClass2 getMyVar]);
return NSApplicationMain(argc, (const char **) argv);
}
----------------------------------*/
which outputs the following
2008-03-27 14:34:31.040 TimeKeeper[790:10b] 1 before = 0
2008-03-27 14:34:31.045 TimeKeeper[790:10b] 2 before = 0
2008-03-27 14:34:31.046 TimeKeeper[790:10b] 1 after 1 = 1
2008-03-27 14:34:31.047 TimeKeeper[790:10b] 2 after 1 = 1
2008-03-27 14:34:31.048 TimeKeeper[790:10b] 1 after 2 = 2
2008-03-27 14:34:31.049 TimeKeeper[790:10b] 2 after 2 = 2
I want it so that it outputs
2008-03-27 14:34:31.040 TimeKeeper[790:10b] 1 before = 0
2008-03-27 14:34:31.045 TimeKeeper[790:10b] 2 before = 0
2008-03-27 14:34:31.046 TimeKeeper[790:10b] 1 after 1 = 1
2008-03-27 14:34:31.047 TimeKeeper[790:10b] 2 after 1 = 0
2008-03-27 14:34:31.048 TimeKeeper[790:10b] 1 after 2 = 1
2008-03-27 14:34:31.049 TimeKeeper[790:10b] 2 after 2 = 1
Thank you,
Justin Giboney
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