遇到一个后台下发16进制的颜色字符串,动态控制app的控件颜色需求;发现项目中已有的颜色字符串转UIColor方法有问题导致转换后的颜色错误.网上大有些此类的转换方法可能存在类似问题,不敢贸然使用,项木禁止引入第三方库,所以就参考YYkit 的UIColor分类进行修改实现了这个方法.在此记录下,方便日后使用.

static inline NSUInteger hexStrToInt(NSString *str) {
    uint32_t result = 0;
    sscanf([str UTF8String], "%X", &result);
    return result;
}

static BOOL hexStrToRGBA(NSString *str,
                         CGFloat *r, CGFloat *g, CGFloat *b, CGFloat *a) {
    
    
    str = ({ // Trim blank characters (space and newline) in head and tail.
        NSCharacterSet *set = [NSCharacterSet whitespaceAndNewlineCharacterSet];
        [[str stringByTrimmingCharactersInSet:set] uppercaseString];
        
    });
    
    if ([str hasPrefix:@"#"]) {
        str = [str substringFromIndex:1];
    } else if ([str hasPrefix:@"0X"]) {
        str = [str substringFromIndex:2];
    }
    
    NSUInteger length = [str length];
    //         RGB            RGBA          RRGGBB        RRGGBBAA
    if (length != 3 && length != 4 && length != 6 && length != 8) {
        return NO;
    }
    
    //RGB,RGBA,RRGGBB,RRGGBBAA
    if (length < 5) {
        *r = hexStrToInt([str substringWithRange:NSMakeRange(0, 1)]) / 255.0f;
        *g = hexStrToInt([str substringWithRange:NSMakeRange(1, 1)]) / 255.0f;
        *b = hexStrToInt([str substringWithRange:NSMakeRange(2, 1)]) / 255.0f;
        if (length == 4)  *a = hexStrToInt([str substringWithRange:NSMakeRange(3, 1)]) / 255.0f;
        else *a = 1;
    } else {
        *r = hexStrToInt([str substringWithRange:NSMakeRange(0, 2)]) / 255.0f;
        *g = hexStrToInt([str substringWithRange:NSMakeRange(2, 2)]) / 255.0f;
        *b = hexStrToInt([str substringWithRange:NSMakeRange(4, 2)]) / 255.0f;
        if (length == 8) *a = hexStrToInt([str substringWithRange:NSMakeRange(6, 2)]) / 255.0f;
        else *a = 1;
    }
    return YES;
}

+ (instancetype)colorWithHexString:(NSString *)hexStr {
    CGFloat r, g, b, a;
    if (hexStrToRGBA(hexStr, &r, &g, &b, &a)) {
        return [UIColor colorWithRed:r green:g blue:b alpha:a];
    }
    return nil;
}