iOS 常用RGB十六进制颜色转换方法

需求

正常美术出图都是给你十六进制编码，然后让我们在Xcode中，对颜色进行赋值，由于iOS的UIColor并未提供方法直接使用十六进制编码对设置颜色的场景进行赋值，所以我们需要造个小轮子。

实现方式

通过分类的方法实现：

UIColor+Addition.h

@interface UIColor (Addition)

//设置RGB颜色
+ (UIColor *)red:(NSInteger)red green:(NSInteger)green blue:(NSInteger)blue alpha:(CGFloat)alpha;
//将颜色转换成RGB
+ (NSArray *)convertColorToRGB:(UIColor *)color;
//设置十六进制颜色
+ (UIColor *)colorWithHex:(NSInteger)hex;
+ (UIColor *)colorWithHexString:(NSString *)hexString;
+ (UIColor *)colorWithHexString:(NSString *)hexString alpha:(CGFloat)alpha

@end

UIColor+Addition.m

#import "UIColor+Addition.h"

@implementation UIColor (Addition)

+ (UIColor *)red:(NSInteger)red green:(NSInteger)green blue:(NSInteger)blue alpha:(CGFloat)alpha {
    return [UIColor colorWithRed:red/255.0 green:green/255.0 blue:blue/255.0 alpha:alpha];
}

+ (NSArray *)convertColorToRGB:(UIColor *)color {
    NSInteger numComponents = CGColorGetNumberOfComponents(color.CGColor);
    NSArray *array = nil;
    if (numComponents == 4) {
        const CGFloat *components = CGColorGetComponents(color.CGColor);
        array = @[@((int)(components[0] * 255)),
                  @((int)(components[1] * 255)),
                  @((int)(components[2] * 255))];
    }
    return array;
}

+ (UIColor *)colorWithHex:(NSInteger)hex {
    return [UIColor colorWithRed:((float)((hex & 0xff0000) >> 16))/255.0 green:((float)((hex & 0x00ff00) >> 8))/255.0 blue:((float)(hex & 0x0000ff))/255.0 alpha:1.0];
}

+ (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:
            blue=0;
            green=0;
            red=0;
            alpha=0;
            break;
    }
    return [UIColor colorWithRed: red green: green blue: blue alpha: alpha];
}

+ (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 alpha:(CGFloat)alpha
{
    NSString *cString = [[hexString stringByTrimmingCharactersInSet:
                          [NSCharacterSet whitespaceAndNewlineCharacterSet]] uppercaseString];
    
    if ([cString length] < 6) {
        return [UIColor whiteColor];
    }
    
    if ([cString hasPrefix:@"#"]) {
        cString = [cString substringFromIndex:1];
    }
    
    if ([cString length] != 6) {
        return [UIColor whiteColor];
    }
    
    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];
    
    return [UIColor colorWithRed:((float) r/255.0f)
                           green:((float) g/255.0f)
                            blue:((float) b/255.0f)
                           alpha:alpha];
}

思考与总结：

需要记住的是：

纯黑是 #000000
纯白是 #FFFFFF