Question

I’ve created a custom button called TaskUIButton that inherits from UIButton. The only difference I have right now is a “va” property.

Here’s the interface

// TaskUIButton.h
@interface TaskUIButton : UIButton 
{
NSString *va;
}
@property(nonatomic, retain) NSString *va;
@end

And the implementation file

//TaskUIButton.m
@implementation TaskUIButton
@synthesize va;

@end

Now, I’ve got an action that I’m using which I want to use to set and retrieve the va property of a button (just for testing/experimentation of course).

Here is where the button action is

- (IBAction)setAndRetrieveVa:(id)sender{

TaskUIButton *imaButton = [TaskUIButton buttonWithType:UIButtonTypeRoundedRect];
imaButton.va = @"please work";
NSLog(@"%@", imaButton.va);
}

Upon activating the setAndRetrieveVa: action, my app crashes with:

-[UIRoundedRectButton setVa:]: unrecognized selector sent to instance 0x4b3a5a0

I’m sure that its a stupid mistake on my part, but I’ve been going at it for a while and would love some insight!

Thanks!

Answer 1

You are getting this because buttonWithType: is returning a new object which is a UIRoundedRectButton object which is a subclass of UIButton. You can’t alter this behavior of the method unless you override but you are unlikely to get what you want. You should take the alloc-init approach.

Using Associative References

You will need to #import <Foundation/NSObjCRuntime.h> for this to work.

To set,

objc_setAssociatedObject(button, "va", @"This is the string", OBJC_ASSOCIATION_RETAIN);

And to retrieve,

NSString * va = (NSString *)objc_getAssociatedObject(button, "va");

This way you wouldn’t need to subclass UIButton.