Question

I have a collection of Objective-C classes that get sub-classed at a variety of different depths by a variety of different classes. Once the entire object is initialized (all of the sub-classes init functions have finished), I need to run an “Update Cache” method which then gets Overridden by the sub-classes as needed.

My Problem:
With a variety of different inheritance depths to my class tree, there is no one place where I can put [self UpdateCache] and I can be sure that there is no sub-class that has not been initialized. The only possible solution would be to call [super init] after the initialization of each class so that the parent class is always called last. I want to avoid this as this goes against all guidelines of writing Objective-C. Is there any clean solution to this problem?

Here is an some example code:

@interface ClassA : NSObject

-(void)UpdateCache
@end

@interface ClassB : ClassA

-(void)UpdateCache
@end

@interface ClassC : ClassB

-(void)UpdateCache
@end

Now for the implementation we need to somehow get UpdateCahce to be called after we know all sub classes have initialized regardless of which class has been initialized

@implementation A
-(id)init
{
   if(self = [super init])
   {
       // Placing [self UpdateCache] here would make it be called prior to 
       // B and C's complete init function from being called.
   }
}

-(void)UpdateCache
{

}


@end

@implementation B
-(id)init
{
   if(self = [super init])
   {
       // Placing [self UpdateCache] would result in UpdateChache not being
       // called if you initialized an instance of Class A
   }
}

-(void)UpdateCache
{
   [super UpdateCache];
}

@end

@implementation C
-(id)init
{
   if(self = [super init])
   {
       // Placing [self UpdateCache] would result in UpdateChache not 
       //being called if you initialized an instance of Class A or B
   }
}

-(void)UpdateCache
{
   [super UpdateCache];
}

@end

Answer 1

Do your sub-classes require unique init method signatures? (e.g. sub-class specific parameters required to initialize the object) If not, following a simple factory-like design pattern may work fine.

Example of what to add your parent/base class:

+(id)buildSelf {
    YourParentClass* obj = [[[self alloc] init] autorelease];
    if (obj) {
        [obj updateCache];
    }
    return obj;
}

Add parameters to it, for all sub-classes to use, if needed.

Again, if your sub-classes need to support unique init method signatures then this won’t work so well.