iphone - Subclass UIButton to add a property

Question

I'd like to subclass UIButton to add some properties that i need (not methods... only properties).

Here the code of my subclass:

//.h-----------------------
@interface MyButton : UIButton{
    MyPropertyType *property;
}

@property (nonatomic,retain) MyPropertyType *property;
@end

//.m--------------------------
@implementation MyButton
@synthesize property;

@end

And here how I use the class:

MyButton *btn = ((MytButton *)[MyButton buttonWithType:UIButtonTypeRoundedRect]);
btn.property = SomeDataForTheProperty;

From where i obtain this error :

 -[UIRoundedRectButton setProperty:]: unrecognized selector sent to instance 0x593e920

Thus, from ButtonWithType i obtain a UIRoundedRectButton and (Mybutton *) can't cast it... What i have to do to obtain a MyButton object ? is -init the unique solution ?

Thank you!

Answer 1

Try using a category with Associative References instead. It is much cleaner and will work on all instances of UIButton.

UIButton+Property.h

#import <Foundation/Foundation.h>

@interface UIButton(Property)

@property (nonatomic, retain) NSObject *property;

@end

UIButton+Property.m

#import "UIButton+Property.h"
#import <objc/runtime.h>

@implementation UIButton(Property)

static char UIB_PROPERTY_KEY;

@dynamic property;

-(void)setProperty:(NSObject *)property
{
    objc_setAssociatedObject(self, &UIB_PROPERTY_KEY, property, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

-(NSObject*)property
{
    return (NSObject*)objc_getAssociatedObject(self, &UIB_PROPERTY_KEY);
}

@end

//Example usage

#import "UIButton+Property.h"

...

UIButton *button1 = [UIButton buttonWithType:UIButtonTypeRoundedRect];
button1.property = @"HELLO";
NSLog(@"Property %@", button1.property);
button1.property = nil;
NSLog(@"Property %@", button1.property);