NSString 长用方法

<1>常用创建方法

//实例化方法创建

- (instancetype)initWithString:(NSString *)aString；

• - (instancetype)initWithFormat:(NSString *)format, …;
• - (instancetype)initWithUTF8String:(const char *)bytes;
• //类方法创建
• + (instancetype)stringWithString:(NSString *)aString；
• +  (instancetype)stringWithFormat:(NSString *)format,, …；
• + (instancetype)stringWithUTF8String:(const char *)bytes；
• <2>求字符串长度
• - (NSUInteger)length;
• <3>通过索引获取相应的字符
• - (unichar)characterAtIndex:(NSUInteger)index;
• <4>字符串比较
• //判断两个字符串是否相等 
• - (BOOL)isEqualToString:(NSString *)aString；
• //比较两个字符串大小
• - (NSComparisonResult)compare:(NSString *)aString；
• //不区分大小写比较大小
• - (NSComparisonResult)caseInsensitiveCompare:(NSString *)aString;
• <5>字符串查找
• - (NSRange)rangeOfString:(NSString *)aString;

• <6>判断前后缀

- (BOOL)hasPrefix:(NSString *)aString;

- (BOOL)hasSuffix:(NSString *)aString;

• <7>数字串转化为数字
• - (double)doubleValue;
• - (float)floatValue;
• - (int)intValue;
• - (NSInteger)integerValue ;
• - (long long)longLongValue ;
• - (BOOL)boolValue ;  
• <8>大小写转换
• - (NSString *)uppercaseString;
• - (NSString *)lowercaseString;
• - (NSString *)capitalizedString; // 首字母大写
• <9>字符串提取
• - (NSString *)substringFromIndex:(NSUInteger)from;
• - (NSString *)substringToIndex:(NSUInteger)to;
• - (NSString *)substringWithRange:(NSRange)range;
•   <10>从本地读取文件内容
• - (id)initWithContentsOfFile:(NSString *)path encoding:(NSStringEncoding)enc error:(NSError **)error;
• + (id)stringWithContentsOfFile:(NSString *)path encoding:(NSStringEncoding)enc error:(NSError **)error;

• <11>字符串分割
• //按照字符串整体分割  
• - (NSArray *)componentsSeparatedByString:(NSString *)separator;
• //按照字符集合分割

•  // NSCharacterSet格式: (NSCharacterSet * set = [NSCharacterSet characterSetWithCharactersInString:@", !.;?"];)

• - (NSArray *)componentsSeparatedByCharactersInSet:(NSCharacterSet *)separator
• 2.2 NSMutableString
• <1>指定索引插入子串
•   - (void)insertString:(NSString *)aString atIndex:(NSUInteger)loc;

<2>删除指定范围的子串

• - (void)deleteCharactersInRange:(NSRange)range;
•        <3>追加子串
• - (void)appendString:(NSString *)aString;
•        <4>追加格式化子串
• - (void)appendFormat:(NSString *)format, ... ;
•        <5>修改子串
• - (void)setString:(NSString *)aString;