Question

My code functions properly, but I am getting warnings, so I think I can do this better. I have a subclass of NSObject (Objects) and I have a subclass of Objects (subObject). I have a property declared in subObjects. I store many objects that are all different subclasses of Objects in a single NSMutableArray. Sometimes, I go through the array and do certain things to certain objects. I read from my array like this:

//I have declared an Objects "myObject" earlier in my code.
//c is an int used to select an object from the array
myObject = [arrayObjects objectAtIndex:c];

In this case, I am accessing my property declared in subObject as

[myObject property]

The code works because I have it set up so it should not be able to get to this piece of code without being a subObject. However, I am getting a warning because the computer does not know this. It only knows that myObject is an Objects, not a subObject. How do I fix this and get rid of the warning?

Answer 1

If it is sure that all objects in the NSMutableArray are of type SubObject (type names should start with an upper case character), then you have these possibilities:

• you can declare the item you extract as SubObject directly:

  SubObject *myObject = [arrayObjects objectAtIndex: c];
  [myObject setProperty: 17];
  

• or you cast:

  Object *myObject = [arrayObjects objectAtIndex: c];
  [(SubObject*)myObject setProperty: 17];
  

• or you simply use id. If you use id, the compiler assumes nothing and will not issue a warning:

  id myObject = [arrayObjects objectAtIndex: c];
  [myObject setProperty: 17];