Need to declare a public instance variable in Objective-C

objective-c visibility public ivar
easythrees picture easythrees · Jul 7, 2013 · Viewed 17.1k times · Source

I'm trying to declare some instance variables for a custom button class in Objective-C (for iOS):

@interface PatientIDButton : UIButton {
    NSUInteger patientID;
    NSString * patientName;
}
@end

However, these are now private and I need them accessible to other classes. I guess I could make accessor functions for them, but how would I make the variables themselves public?

Answer

Sergey Kalinichenko picture Sergey Kalinichenko · Jul 7, 2013

To make instance variables public, use @public keyword, like this:

@interface PatientIDButton : UIButton {
    // we need 'class' level variables
    @public NSUInteger patientID;
}
@end

Of course you need to remember all the standard precautions of exposing "raw" variables for public access: you would be better off with properties, because you would retain flexibility of changing their implementation at some later time.

Finally, you need to remember that accessing public variables requires a dereference - either with an asterisk or with the -> operator:

PatientIDButton *btn = ...
btn->patientID = 123; // dot '.' is not going to work here.

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