NSAttributedString

NSAttributedString维护了一个NSString，用来保存最原始的字符串，另有一个NSDictionary用来保存各个子串/字符的属性。

创建AttributedString演示样例：
UIFont *font = [UIFont fontWithName:@"Courier" size:18.0];
NSDictionary *attriDict = [NSDictionary dictionaryWithObject:font forKey:NSFontAttributeName];
NSAttributedString *attriStr = [[NSAttributedString alloc] initWithString:@"my attributed string" attributes:attriDict];
self.label.attributedText = attriStr;

一些常见属性：
字体
UIKIT_EXTERN NSString *const NSFontAttributeName NS_AVAILABLE_IOS(6_0);                // UIFont, default Helvetica(Neue) 12

文字颜色, 前景色
UIKIT_EXTERN NSString *const NSForegroundColorAttributeName NS_AVAILABLE_IOS(6_0);     // UIColor, default blackColor

// 背景色
UIKIT_EXTERN NSString *const NSBackgroundColorAttributeName NS_AVAILABLE_IOS(6_0);     // UIColor, default nil: no background

// strike-through line 中划线
UIKIT_EXTERN NSString *const NSStrikethroughStyleAttributeName NS_AVAILABLE_IOS(6_0);  // NSNumber containing integer, default 0: no strikethrough

// strike-though line 颜色
UIKIT_EXTERN NSString *const NSStrikethroughColorAttributeName NS_AVAILABLE_IOS(7_0);  // UIColor, default nil: same as foreground color

// underline-style 下划线
UIKIT_EXTERN NSString *const NSUnderlineStyleAttributeName NS_AVAILABLE_IOS(6_0);      // NSNumber containing integer, default 0: no underline

// 下划线颜色
UIKIT_EXTERN NSString *const NSUnderlineColorAttributeName NS_AVAILABLE_IOS(7_0);      // UIColor, default nil: same as foreground color

// 字体粗度
UIKIT_EXTERN NSString *const NSStrokeWidthAttributeName NS_AVAILABLE_IOS(6_0);         // NSNumber containing floating point value, in percent of font point size, default 0: no stroke; positive for stroke alone, negative for stroke and fill (a typical value for outlined text would be 3.0)

// 模糊度
UIKIT_EXTERN NSString *const NSShadowAttributeName NS_AVAILABLE_IOS(6_0);              // NSShadow, default nil: no shadow
     NSShadow *shadow = [[NSShadow alloc] init];
    shadow.shadowBlurRadius = 5;  // 模糊度
    shadow.shadowColor = [UIColor blackColor];
    shadow.shadowOffset = CGSizeMake(1, 3);
    NSShadowAttributeName:shadow

倾斜
UIKIT_EXTERN NSString *const NSObliquenessAttributeName NS_AVAILABLE_IOS(7_0);         // NSNumber containing floating point value; skew to be applied to glyphs, default 0: no skew