UIColor与十六进制字符串互转（整理）

UIColor转十六进制字符串

方法一：经过测试发现部分颜色会转化为#fffff（五个f），转化残缺导致最后颜色无法还原，不推荐使用。

// UIColor转#ffffff格式的字符串
+ (NSString *)hexFromUIColor:(UIColor *)color
{
    if (CGColorGetNumberOfComponents(color.CGColor) < 4) {
        const CGFloat *components = CGColorGetComponents(color.CGColor);
        color = [UIColor colorWithRed:components[0]
                                green:components[0]
                                 blue:components[0]
                                alpha:components[1]];
    }

    if (CGColorSpaceGetModel(CGColorGetColorSpace(color.CGColor)) != kCGColorSpaceModelRGB) {
        return [NSString stringWithFormat:@"#FFFFFF"];
    }

    return [NSString stringWithFormat:@"#%x%x%x", (int)((CGColorGetComponents(color.CGColor))[0]*255.0),
            (int)((CGColorGetComponents(color.CGColor))[1]*255.0),
            (int)((CGColorGetComponents(color.CGColor))[2]*255.0)];
}

方法二：完美转化为#ffffff格式，暂未发现问题，推荐使用。

// UIColor转#ffffff格式的字符串
+ (NSString *)hexStringFromColor:(UIColor *)color {
    const CGFloat *components = CGColorGetComponents(color.CGColor);

    CGFloat r = components[0];
    CGFloat g = components[1];
    CGFloat b = components[2];

    return [NSString stringWithFormat:@"#%02lX%02lX%02lX",
            lroundf(r * 255),
            lroundf(g * 255),
            lroundf(b * 255)];
}

十六进制字符串转UIColor

方法一：

+ (CGFloat) colorComponentFrom: (NSString *) string start: (NSUInteger) start length: (NSUInteger) length {
    NSString *substring = [string substringWithRange: NSMakeRange(start, length)];
    NSString *fullHex = length == 2 ? substring : [NSString stringWithFormat: @"%@%@", substring, substring];
    unsigned hexComponent;
    [[NSScanner scannerWithString: fullHex] scanHexInt: &hexComponent];
    return hexComponent / 255.0;
}

+ (UIColor *) colorWithHexString: (NSString *) hexString {
    NSString *colorString = [[hexString stringByReplacingOccurrencesOfString: @"#" withString: @""] uppercaseString];
    CGFloat alpha, red, blue, green;
    switch ([colorString length]) {
        case 3: // #RGB
            alpha = 1.0f;
            red   = [self colorComponentFrom: colorString start: 0 length: 1];
            green = [self colorComponentFrom: colorString start: 1 length: 1];
            blue  = [self colorComponentFrom: colorString start: 2 length: 1];
            break;
        case 4: // #ARGB
            alpha = [self colorComponentFrom: colorString start: 0 length: 1];
            red   = [self colorComponentFrom: colorString start: 1 length: 1];
            green = [self colorComponentFrom: colorString start: 2 length: 1];
            blue  = [self colorComponentFrom: colorString start: 3 length: 1];
            break;
        case 6: // #RRGGBB
            alpha = 1.0f;
            red   = [self colorComponentFrom: colorString start: 0 length: 2];
            green = [self colorComponentFrom: colorString start: 2 length: 2];
            blue  = [self colorComponentFrom: colorString start: 4 length: 2];
            break;
        case 8: // #AARRGGBB
            alpha = [self colorComponentFrom: colorString start: 0 length: 2];
            red   = [self colorComponentFrom: colorString start: 2 length: 2];
            green = [self colorComponentFrom: colorString start: 4 length: 2];
            blue  = [self colorComponentFrom: colorString start: 6 length: 2];
            break;
        default:
            return nil;
    }
    return [UIColor colorWithRed: red green: green blue: blue alpha: alpha];
}

方法二：

+ (UIColor *)colorWithHexString:(NSString *)hexString alpha:(CGFloat)alphaValue {
    NSString *cString = [[hexString stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] uppercaseString];
    if (cString.length < 6)
    return [UIColor clearColor];
    if ([cString hasPrefix:@"0X"])
    cString = [cString substringFromIndex:2];
    if ([cString hasPrefix:@"#"])
    cString = [cString substringFromIndex:1];
    if (cString.length != 6)
    return [UIColor clearColor];
    NSRange range;
    range.location = 0;
    range.length = 2;
    NSString *rString = [cString substringWithRange:range];
    range.location = 2;
    NSString *gString = [cString substringWithRange:range];
    range.location = 4;
    NSString *bString = [cString substringWithRange:range];
    unsigned int r, g, b;
    [[NSScanner scannerWithString:rString] scanHexInt:&r];
    [[NSScanner scannerWithString:gString] scanHexInt:&g];
    [[NSScanner scannerWithString:bString] scanHexInt:&b];
    // 注意：myColor是自定义宏
    //#define myColor(R, G, B, A) [UIColor colorWithRed:R/255.0 green:G/255.0 blue:B/255.0 alpha:A]
    return myColor(r, g, b, alphaValue);
}