CODEWITHSUNDEEP
objective-ciospropertiesuilabelsubclass
JonN
JonN

Reputation: 2568

UILabel Subclass appears as UILabel in Objective-C

I'm a experienced C++ programmer trying to create my first Objective-C subclass of UILabel with an added read-only property

// UINumericlabel.h
@interface UINumericLabel : UILabel

// Returns true if the numeric display contains a decimal point
@property (readonly,nonatomic) BOOL hasDecimalPoint;
@end

//  UINumericLabel.m

#import "UINumericLabel.h"

@implementation UINumericLabel
// Returns true if the numeric display contains a decimal point
- (BOOL) hasDecimalPoint;
{
   return [self.text rangeOfString:(@".")].location != NSNotFound;
}
@end

When I try to reference the hasDecimalPoint property for an instantiated UINumericLabel I get an abort with error 2012-02-20 18:25:56.289 Calculator[10380:207] -[UILabel hasDecimalPoint]: unrecognized selector sent to instance 0x684c5c0

In the debugger it shows my declaration of a UINumericLabel property as being a UILabel * Do I need to override the (id)init for UILabel in my UINumericLabel subclass? How do I do that?

#import "UINumericLabel.h"

@interface CalculatorViewController : UIViewController <ADBannerViewDelegate>
@property (weak, nonatomic) IBOutlet UINumericLabel *display0;
@end

When I hover over display0P in the debugger it says it is a UILabel * not a UINumericLabel *

UINumericLabel * display0P = self.display0;

Upvotes: 0

Views: 1600

Answers (2)

danh
danh

Reputation: 62676

I agree with @Brian above, but would add two things: (1) no need for a declared property unless you plan to cache the BOOL value. Just use a method with a predeclaration in .h, and (2) no need for a subclass in this case. A better approach would be an extension, like: UILabel+JonN.h...

@interface UILabel (JonN)

-(BOOL)hasDecimal;

@end

Then, in UILabel+JonN.m...

@implementation UILabel (JonN)

// your method as written

@end

This is prettier, I think, and solves the problem you were having with IB (which I think @Brian correctly addressed).

Upvotes: 0

Brian
Brian

Reputation: 3601

In the Interface Builder select the label and then open the Identity Inspector. In the text field "Class" it probably says UILabel. Change that to be your new subclass, UINumericLabel.

Upvotes: 7

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