Question

In my app I use a class (which is a singleton for now), called ClassA for the example, for managing stuff.

Because it’s a singleton, I used this behavior to get this unique instance in many classes that needs it.

But now, i can’t keep this class as a singleton anymore, I need to have one instance by NSDocument.

So I created an instance of the ClassA on my NSDocument subclass but the problem is for passing this object on classes that needs it.

I have this kind of structure :

Class1 <- Class2 <- Class3 <- Document -> ClassA

I need to have access of the instance of ClassA of Document in Class1.

I can use Dependency Injection to pass ClassA in Class1 by init or setter methods but because Document does not have direct access to Class1, I need to pass it to Class3 then Class2 then Class1.

Is this the only way to do that ? Or are there another better ways to handle it?

Answer 1

I would say go back to your singleton principle but use the NSDocument as the key into a dictionary of ClassA objects; something like:

static NSMutableDictionary *_classCache = [[NSMutableDictionary alloc] init];

+ (ClassA *)classAForDocument:(NSDocument *)document
{
    ClassA *classA = [_classCache objectForKey:document];
    if (classA == nil)
    {
       // Initialise with something specific to the document I guess...
        classA = [[ClassA alloc] init];
        [_classCache setObject:classA forKey:document];
    }
    return classA;
}

This then only requires that Class{1,2,3} know the document they belong to.