CODEWITHSUNDEEP
objective-coopparent-child
Colas
Colas

Reputation: 3573

How to define a child object based upon a parent object?

this is a general question. I can divide my questions into two :

I have a class ChildClass that herits from ParentClass.

1) I would like to define a initFromParentClass method, whose signature would be

       - (id) initFromParentClass:(ParentClass)anObjectFromTheParentClass

which would create a new instance of ChildClass, based upon anObjectFromTheParentClass — that is, all the attributes of the new instance are "copied" from the ones of the "parent instanc".

2) Can these two parent/child objects be dynamically linked ? Ie : if the parent changes, the child changes ?

Thank you

Upvotes: 0

Views: 135

Answers (1)

Mark Bernstein
Mark Bernstein

Reputation: 2080

One familiar idiom is to treat let the child class delegate existing methods to an instance of the parent:

 @implementation ChildClass
 @property (nonatomic, strong) ParentClass *obj;
 - (void) mill
 {
      [obj mill];
 }

 - (NSInteger) count
 {
       return [obj count];
 }

This can be tedious and hard to maintain if ParentClass has a broad and rapidly-changing API. In that case, you might not want to inherit at all, but rather to extract a common interface from ParentClass and ChildClass, and perhaps let instances of ChildClass observe changes to the object from which they were initialized.

Upvotes: 1

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