objective C: Buttons created from subclass of UIButton class not working

Question

I am creating a subclass of UIButton in order to create my own customized buttons. My code as follows:

//interface file (subclass of uIButton
@interface UICustomButton : UIButton 
{
    Answer *answer;
    NSString *btnType;
}

@property (nonatomic, retain) Answer *answer;
@property (nonatomic, assign) NSString *btnType;

- (id)initWithAnswer:(Answer *)ans andButtonType:(NSString *)type andFrame:(CGRect)frame; 
- (void)buttonPressed;

@end


//Implementation file (.m)
@implementation UICustomButton
@synthesize answer,btnType;

- (id)initWithAnswer:(Answer *)ans andButtonType:(NSString *)type andFrame:(CGRect)frame; 
{
    self = [super initWithFrame:frame];
    if (self) 
    {
        self = [[UIButton alloc]initWithFrame:CGRectMake(0, 0, frame.size.width, frame.size.height)];
        self.backgroundColor = [UIColor colorWithHexString:@"#E2E4E7"];

    }

    [self addTarget:self action:@selector(buttonPressed) forControlEvents:UIControlStateNormal];

    self.answer = ans;
    self.btnType = type;

    return self;
}

I am facing some issues in getting the above code to work. I have 2 problems

1) The buttons are not responding to the selector method "buttonPressed"

2) I am hitting a runtime error for the lines 'self.answer = ans' and 'self.btnType = type' Stack trace as follows:

-[UIButton setAnswer:]: unrecognized selector sent to instance 0x614ebc0
2011-06-23 00:55:27.038 onethingaday[97355:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[UIButton setAnswer:]: unrecognized selector sent to instance 0x614ebc0'

What am I doing wrong here?

Answer 1

This is happening because you are creating a UIButton type object and not a UICustomButton type inside the init method when you do

self = [[UIButton alloc]initWithFrame:CGRectMake(0, 0, frame.size.width, frame.size.height)];

Try replacing your init method for

- (id)initWithAnswer:(Answer *)ans andButtonType:(NSString *)type andFrame:(CGRect)frame; 
{
    self = [self initWithFrame:CGRectMake(0, 0, frame.size.width, frame.size.height)];
    if (self) 
    {
        self.backgroundColor = [UIColor colorWithHexString:@"#E2E4E7"];

        [self addTarget:self action:@selector(buttonPressed) forControlEvents:UIControlEventTouchUpInside];

        self.answer = ans;
        self.btnType = type;
    }

    return self;
}

This will cause self to be a UICustomButton type object.

Also, you are using a wrong type for the UIControlState parameter when you add the target to your button using the addTarget:action:forControlEvents: method

You should use value among the ones bellow:

UIControlEventTouchDown
UIControlEventTouchDownRepeat
UIControlEventTouchDragInside
UIControlEventTouchDragOutside
UIControlEventTouchDragEnter
UIControlEventTouchDragExit
UIControlEventTouchUpInside
UIControlEventTouchUpOutside
UIControlEventTouchCancel

---

EDIT: Notes on UIButton subclassing

Many references on the web say you should NOT subclass the UIButton class, but not only anybody said why but what also deeply annoyed me was that the UIButton Class Reference does not say anything about it at all.

If you take UIWebView Class Reference for example, it explicitly states that you should not subclass UIWebView

Subclassing Notes The UIWebView class should not be subclassed.

the big deal with UIButton is that it inherits from UIControl and a good and simple explanation is on the UIControl Class Reference itself

Subclassing Notes You may want to extend a UIControl subclass for either of two reasons:

• To observe or modify the dispatch of action messages to targets for particular events
• To provide custom tracking behavior (for example, to change the highlight appearance)

So, this means that you CAN subclass a UIButton, but you should be careful on what you are doing. Just subclass it to change its behavior and not its appearance. To modify a UIButton appearance you should use the interface methods provided for that, such as:

setTitle:forState:
setBackgroundImage:forState:
setImage:forState:

References worth reading

• The UIView Programming Guide: View and Window Architecture -> Tips for Using Views Effectively -> Do Not Customize Controls by Embedding Subviews

Source: my post here

Answer 2

Not sure this was in the docs before, but anyway these are the current notes on + (id)buttonWithType:(UIButtonType)buttonType...

To me it looks like subclassing is OK as long as you use init instead of buttonWithType. I have yet to try it myself however.

Discussion This method is a convenience constructor for creating button objects with specific configurations. It you subclass UIButton, this method does not return an instance of your subclass. If you want to create an instance of a specific subclass, you must alloc/init the button directly.

When creating a custom button—that is a button with the type UIButtonTypeCustom—the frame of the button is set to (0, 0, 0, 0) initially. Before adding the button to your interface, you should update the frame to a more appropriate value.