NSAttributedString

NSAttributedString 管理character strings,属性的集合，可以设置单个character的或string中的部分字符的属性

characters和attributes之间的联系称之为attributed string

NSAttributedString:read only attributed string

NSMutableAttributedString: 即可读又可写的字符串

一个attributed string用name 来识别attribute，用NSDictionary对象来存储value和attributed name.可以分配任何attributed name和value pairs应用到选定范围的characters上，

in ios: standard attributed keys定义在：NSAttributedString UIKit Additions reference

in os x:standard attributed keys定义在：NSAttributedString application kit Additions reference

NSAttributedString并不是一个NSString的一个子类，它包含一个应用attribute的NSString对象，NSAttributedString采纳了NSCopying和NSMutableCopying协议，这使得转换NSAttributedString到另外一个变得容易

一个属性字符串通过名字来识别属性，用一个NSDictionary对象来存储attribute的值，text font用名字NSFontAttributedName对应的NSFont对象来存储，

可以用不同的方式来创建NSAttributedString

可以用initWithString:,initWithString:attributes:,initWithAttributedString:,这些方法用你提供的数据来创建一个attributed string

NSFont  *font=[NSFont  fontWithName:@"Palatino-Roman",size:14.0];

NSDictionary *attrDictionary =[NSDictionary dictionaryWithObject:font forKey:NSFontAttributedName];

NSAttributedString *attrString = [[NSAttributedString alloc]initWIthString:@"string1" attributes:attrDictionary];

被分配给attributed string的 attributes value变成string的property,是不能被别的对象更改的

可以用NSMutableAttributedString的方法：setAttributeds:range:来设定在某一个范围内的属性值

用RTF格式和RTFD格式的数据来创建一个attributed string

NSData *rtfData = ...; // assume rtfData is an NSData object containing valid RTF data

NSDictionary *docAttributes;

NSSize paperSize;

NSAttributedString *attrString;

if ((attrString = [[NSAttributedString alloc]

initWithRTF: rtfData documentAttributes: &docAttributes])) {

NSValue *value = [docAttrs objectForKey:@"PaperSize"];

paperSize = [value sizeValue];

// implementation continues...

对不可改变的attributed string，当创建attributedString时就必须指明他的所有属性

在Objective-c中用方法：initWithString:attributes:  参数中用一个NSDictionary object来存储attribute name和value

或者用initWithString：不指明任何属性

从一个Attributed string中取出attribute value的方法

• attributesAtIndex:effectiveRange:

• attributesAtIndex:longestEffectiveRange:inRange:

• attribute:atIndex:effectiveRange:

• attribute:atIndex:longestEffectiveRange:inRange:

• fontAttributesInRange:

• rulerAttributesInRange:

前两个方法返回在index处的字符串的所有的属性   return all attributes at a given index

中间两个方法返回在attributedName处的属性值return the value of a single named attribute.

最后两个方法是Application Kit’s extensions ， return attributes defined to apply only to characters or to whole paragraphs, respectively.

在attributedstring中的每一个字符都有他自己的 collection of attributes，然而通常一系列字符的属性和value是相同的

character attributes

key: NSFontAttributeName   value:UIFont对象，设定character 的字体

key:NSParagraphStyleAttributeName value :NSParagraphStyle对象 Use this attribute to apply multiple attributes to a range of text.

key:NSForegroundColorAttributeName value: UIColor Use this attribute to specify the color of the text during rendering

key:NSBackgroundColorAttributedName value:UIColor Use this attribute to specify the color of the background area behind the text

key:NSUnderlineStyleAttributeName value:NSNumber  This value indicates whether the text is underlined

key:NSStrokeColorAttributeName value:UIColor    If it is not defined (which is the case by default), it is assumed to be the same as the value of 

NSForegroundColorAttributeName

; otherwise, it describes the outline color.

key:NSStrokeWidthAttributedName value:NSNumber  Specify positive values to change the stroke width alone. Specify negative values to stroke and fill the text