CODEWITHSUNDEEP
iosobjective-cnsstringobjective-c-category
tentmaking
tentmaking

Reputation: 2146

No Know Class Method in NSString Category

I have a category as defined:

#import <Foundation/Foundation.h>

@interface NSString (MyApp)

+ (UIColor *)colorFromHexString;

@end


#import "NSString+MyApp.h"

@implementation NSString (MyApp)

+ (UIColor *)colorFromHexString
{
    self = [self stringByReplacingOccurrencesOfString:@"#" withString:@""];
    unsigned rgbValue = 0;
    NSScanner *scanner = [NSScanner scannerWithString:hexString];
    [scanner scanHexInt:&rgbValue];
    return [UIColor colorWithRed:((rgbValue & 0xFF0000) >> 16)/255.0 green:((rgbValue & 0xFF00) >> 8)/255.0 blue:(rgbValue & 0xFF)/255.0 alpha:1.0];
}

@end

I am getting an error on the line self = [self stringByReplacingOccurrencesOfString:@"#" withString:@""]; that says: "No know class method for selector stringByReplacingOccurrencesOfString:withString" and "cannot assign self in a class method".

I am confused as to why I am not able to do this in an NSString Category. I've seen examples online that do things very similar with 'self' in an NSString Category so I am not sure why it isn't working here.

Anyone know what I'm doing wrong?

Upvotes: 1

Views: 244

Answers (1)

Sonny Saluja
Sonny Saluja

Reputation: 7287

There are multiple errors in your code.

Use the instance method (-) instead of static method (+)

// INCORRECT. self in a static method points to class object
// + (UIColor *)colorFromHexString

// CORRECT. self is instance method points to instance of class.
- (UIColor *)colorFromHexString

Also on line 1 assign hexString instead of self.

- (UIColor *)colorFromHexString
{
    NSString *hexString = [self stringByReplacingOccurrencesOfString:@"#" withString:@""];
    unsigned rgbValue = 0;
    NSScanner *scanner = [NSScanner scannerWithString:hexString];
    [scanner scanHexInt:&rgbValue];
    return [UIColor colorWithRed:((rgbValue & 0xFF0000) >> 16)/255.0 green:((rgbValue & 0xFF00) >> 8)/255.0 blue:(rgbValue & 0xFF)/255.0 alpha:1.0];
}

Upvotes: 1

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