前言

    NS_CLASS_AVAILABLE_IOS(2_0) @interface UIColor : NSObject <NSSecureCoding, NSCopying>
    @available(iOS 2.0, *)       public class UIColor : NSObject, NSSecureCoding, NSCopying

• UIColor、CIColor 和 CGColor 出现在不同的类库里面，其实就是颜色存储方式不同而已，比如 999 可以用 10 进制、2 进制、16 进制等存储。三者之间都是能够方便转换的，特别是很多构造函数。

1、UIColor 的创建

• Objective-C

  • 使用系统定义好的颜色创建

        UIColor *color1 = [UIColor blueColor];
    
        // 附带设置颜色的透明度
        UIColor *color1 = [[UIColor blackColor] colorWithAlphaComponent:0.5];

  • 由白色透明度创建

        // alpha：透明度，1 不透明
        UIColor *color2 = [UIColor colorWithWhite:1 alpha:0.5];

  • 由三原色创建

        // arc4random()%256/255.0 获取小于等于 1 大于 0 的随机数字
        CGFloat red = arc4random()%256/255.0;
        CGFloat green = arc4random()%256/255.0;
        CGFloat blue = arc4random()%256/255.0;
    
        // Red，green，blue 值的范围是 0 ～ 1，alpha：透明度，1 不透明
        UIColor *color3 = [UIColor colorWithRed:red green:green blue:blue alpha:1];

  • 由图片创建

        UIColor *color4 = [UIColor colorWithPatternImage:[UIImage imageNamed:@"13"]];

  • 由 16 进制字符串创建

        NSString *colorString = @"#FF0000";
    
        // 十六进制数字字符串转十进制数字
        NSString *s1 = [colorString substringWithRange:NSMakeRange(1, 2)];
        unsigned long c1 = strtoul([s1 UTF8String], 0, 16);
    
        NSString *s2 = [colorString substringWithRange:NSMakeRange(3, 2)];
        unsigned long c2 = strtoul([s2 UTF8String], 0, 16);
    
        NSString *s3 = [colorString substringWithRange:NSMakeRange(5, 2)];
        unsigned long c3 = strtoul([s3 UTF8String], 0, 16);
    
        // Red，green，blue 值的范围是 0 ～ 1，alpha：透明度，1 不透明
        UIColor *color5 = [UIColor colorWithRed:c1/255.0 green:c2/255.0 blue:c3/255.0 alpha:1];

• Swift

  • 使用系统定义好的颜色创建

        let color1:UIColor = UIColor.blueColor()
    
        // 附带设置颜色的透明度
        let color1:UIColor = UIColor.blackColor().colorWithAlphaComponent(0.5)

  • 由白色透明度创建

        // alpha：透明度，1 不透明
        let color2:UIColor = UIColor(white: 1, alpha: 0.5)

  • 由三原色创建

        // arc4random()%256/255.0 获取小于等于 1 大于 0 的随机数字
        let red:CGFloat = CGFloat(arc4random()%UInt32(256/255.0))
        let green:CGFloat = CGFloat(arc4random()%UInt32(256/255.0))
        let blue:CGFloat = CGFloat(arc4random()%UInt32(256/255.0))
    
        // Red，green，blue 值的范围是 0 ～ 1，alpha：透明度，1 不透明
        let color3:UIColor = UIColor(red: red, green: green, blue: blue, alpha: 1)

  • 由图片创建

        let color4:UIColor = UIColor(patternImage: UIImage(named: "13")!)

2、UIColor 与 CIColor 和 CGColor 的相互转换

• Objective-C

      // UIColor 转 CGColor
      CGColorRef color = [[UIColor greenColor] CGColor];

• Swift

      // UIColor 转 CGColor
      let color:CGColorRef = UIColor.greenColor().CGColor

3、由十六进制颜色值创建 RGB 颜色值

• 具体实现代码见 GitHub 源码 QExtension

• 适用于 0Xc83c23、#c83c23、c83c23 格式的十六进制颜色值。

      /// 由十六进制颜色值创建 RGB 颜色值，带透明度设置
      + (UIColor *)colorWithHexString:(NSString *)color alpha:(CGFloat)alpha {
  
          NSString *cString = [[color stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] uppercaseString];
  
          // String should be 6 or 8 characters
          if ([cString length] < 6) {
              return [UIColor clearColor];
          }
  
          // strip "0X" or "#" if it appears
          if ([cString hasPrefix:@"0X"])
              cString = [cString substringFromIndex:2];
          if ([cString hasPrefix:@"#"])
              cString = [cString substringFromIndex:1];
          if ([cString length] != 6)
              return [UIColor clearColor];
  
          // Separate into r, g, b substrings
          NSRange range;
          range.location = 0;
          range.length = 2;
  
          // r、g、b
          NSString *rString = [cString substringWithRange:range];
          range.location = 2;
          NSString *gString = [cString substringWithRange:range];
          range.location = 4;
          NSString *bString = [cString substringWithRange:range];
  
          // Scan values
          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];
      }
  
      /// 由十六进制颜色值创建 RGB 颜色值
      + (UIColor *)colorWithHexString:(NSString *)color {
  
          return [UIColor colorWithHexString:color alpha:1.0f];
      }

      // 0X 前缀格式
      UIColor *color = [UIColor colorWithHexString:@"0Xc83c23"];
      UIColor *color = [UIColor colorWithHexString:@"0Xc83c23" alpha:0.5];
  
      // # 前缀格式
      UIColor *color = [UIColor colorWithHexString:@"#c83c23"];
      UIColor *color = [UIColor colorWithHexString:@"#c83c23" alpha:0.5];
  
      // 无前缀格式
      UIColor *color = [UIColor colorWithHexString:@"c83c23"];
      UIColor *color = [UIColor colorWithHexString:@"c83c23" alpha:0.5];