Question

I have created a custom class called RCTextField, whose purpose is to create an NSTextField with rounded corners (thus RC...).

This RCTextField inherits from NSTextField and overrides the drawRect: method in order to create its own rectangle with rounded corners.

Now, I want to do the same thing for NSSecureTextField, that is, have a way to make it have rounded corners. I can’t just make it inherit RCTextField, because that one doesn’t have any secure implementation for text that NSSecureTextField has.

And if I inherit from NSSecureTextField, I’d have to rewrite all the drawRect: implementation again.

An option I thought about would be to have an RCBaseTextField class which contains a static method called drawRect:forNSTextField:withParams:, and call that one in the drawRect: of RCTextField and RCSecureTextField. However, that seems a bit hackish, and it feels like there could be a better OOP way to do this in Objective-C.

So, what would be the best/sanest/software-engineering-“esquest” way to share the draw-rounded-corners code from RCTextField between an RCTextField and an RCSecureTextField?

Answer 1

Unfortunately, you cannot make an Objective-C inherit behavior from more that one other class. I think providing a function (using a Object-Oriented language doesn’t prevent from using functions when they are appropriate) that will be invoked by both drawRect: implementation is the simpler way.

Or you may just ignore NSSecureTextField and make RCSecureTextField inherit from RCTextField. Then implement the class method cellClass to return NSSecureTextFieldCell and you should get the same exact features as NSSecureTextField.

@interface RCSecureTextField : RCTextField
@end

@implementation RCSecureTextField
+ (Class)cellClass { return [NSSecureTextFieldCell class]; }
@end