Shared Ivars

I have an instance variable which returns a double value in the myDocument file in a document based application. I want to use that value in another class. How do you get the value from one class to the other. eg. in “myDocument.m” -(double)value1 { return value1; }

in myClass.m -(double)totalValue

{ return [self value2] + (value1 from myDocument class) }

Value2 is already in myClass, how do you get value 1 (from myDocument) into myClass???? Thanks DSG

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Not sure if I have understood, but I’ll try:

• you get a reference to the myDocument somehow, let’s say by initializing the myClass object like this:

@interface myClass { myDocument* doc; }

• (id) initWithMyDocument:(myDocument*) doc; // methods…

@end

@implementation myClass

• (id) initWithMyDocument:(myDocument*) aDoc { if (self = [super init]) { doc = aDoc; // assumes this object is initialized // by myDocument, so we get a weak // ref which is both faster and avoids // retain cycles. } return self; }

// …

• (void) myMethod { // … someValue = [self value2] + [doc value1]; // … }

// …

@end

Somewhere in myDocument, when you create the myClass instance, you may do:

myClass* inst = myClass alloc] initWithMyDocument:self];

A faster way would be to use outlets in the [[InterfaceBuilder file for your document (create an instance there of myClass with an outlet and attach that outlet to File’s Owner – that is, the myDocument instance).

Remember that a class is just a blueprint for instances, that is, a class has no “values” of its own; it’s just a model used to create instances, which hold these values (it might help to think of the class myDocument as “the abstract concept of a myDocument”, which is then used to create any number of documents on-screen – the instances of this class. Each of them will have a different value1, and you must make sure the instance of myClass references the right instance by getting a reference to it, either manually as above or with outlets).