Question

I have 2 classes in Cocoa, but am unable to access variables from one to the other.

Class1.h:

@interface MyClass : NSOpenGLView
{
int myVar;
}
@property (assign) int myVar;

Class1.m

@implementation MyClass
@synthetize myVar;
...
myVar=5;

Class2.m

MyClass *theClass=[MyClass alloc];
nb=theClass.myVar;

==> nb=0 (instead of 5), and I am sure that the myVar=5 was executed.

What did I wrong ?

Thanks !

Answer 1

In Class2, you are creating a new instance of MyClass, rather than referring to an existing instance where you have previously set the myVar property to 5.

It’s also worth mentioning that, if you needed to create a new instance of MyClass (that you don’t), this line:

MyClass *theClass=[MyClass alloc];

should be:

MyClass *theClass=[[MyClass alloc] init];

From Allocating and Initializing Objects:

It takes two steps to create an object using Objective-C. You must:

• Dynamically allocate memory for the new object
• Initialize the newly allocated memory to appropriate values

An object isn’t fully functional until both steps have been completed.
Each step is accomplished by a separate method but typically in a
single line of code:

id anObject = [[Rectangle alloc] init];