Question

I have a small function which I want to rewrite, so that function is valid for every class.
At the moment I have 10 of the same functions which all work same but every function is for another class.
I know, that I have to do it with reflections, but I am not so sure how to do it.
I already read this link:
http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/ObjCRuntimeRef/Reference/reference.html

The functions I am talking about are:

-(NSCountedSet *)MissionGetReferecedNested:(id)modelObject
{
    setOfObjects = [[NSCountedSet alloc]initWithArray:modelObject.MissionSectionList];
    return setOfObjects;
}
-(NSCountedSet *)MissionGetSectionReferecedNested:(id)modelObject
{
    setOfObjects = [[NSCountedSet alloc]initWithArray:modelObject.DamageAccountList];
    return setOfObjects;
}

MissionSectionList and DamageAccountList are both NSMutableArrays from two different classes.
Is it possible to see if a class consists a NSMutableArray and if yes then it should call the …. modelObject.MyMutableArray?

Answer 1

You can use reflection like this:

- (NSCountedSet *)MissionGet:(id)modelObject
{
    SEL propertySelector = NULL;

    if ([modelObject respondsToSelector:@selector(MissionSectionList)]) {
        propertySelector = @selector(MissionSectionList);
    } else if ([modelObject respondsToSelector:@selector(DamageAccountList)]) {
        propertySelector = @selector(DamageAccountList);
    }

    if (!propertySelector) {
      [NSException raise:@"Invalid modelObject value" format:@"Model object %@ does not contain any recognised selectors", modelObject];
    }

    return [[NSCountedSet alloc] initWithArray:[modelObject performSelector:propertySelector]];
}

But a more common technique among cocoa programmers would be:

- (NSCountedSet *)MissionGet:(id <MyCustomProtocol>)modelObject
{
    return [[NSCountedSet alloc] initWithArray:[modelObject missionArray]];
}

Where you would accept any object which confirms to the protocol MyCustomProtocol. The protocol is defined in a header files somewhere, using:

@protocol MyCustomProtocol

@property (readonly) NSArray *missionArray;

@end

And then in each of your classes, declare it as implementing the protocol:

@interface MissionSectionListClass <MyCustomProtocol>

And add a method implementation:

@implementation MissionSectionListClass <MyCustomProtocol>

- (NSArray *)missionArray
{
    return self.MissionSectionList;
}

@end

Using protocols is a bit more code, but it’s the “right” way to go. It allows you to add support for new classes, without any change to your MissiongGet... method.

More info about protocols: http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjectiveC/Chapters/ocProtocols.html