[TwistedFate]NSString

学习系统类:
1.NSString
自定义初始化方法:

NSString *str1 = [[NSString alloc] initWithFormat:@"wl-%@",@"121"];

便利构造器方法:

NSString *str2 = [NSString stringWithFormat:@" "];

语法糖:
NSString *str = @”222313”;

// 前缀NSLog(@"%d",[str1 hasPrefix:@"wl"]);// 获取字符串长度NSString *str = @"上海蓝鸥科技";NSUInteger length = [char length];NSLog("%lu",length);// 获取子字符串(字符串截取)NSRange range = NSMakeRange(4,2);NSString *strNew = [str substringWithRange:range];NSLog(@"%@",strNew);// 按索引截取 :从索引处截取 一直到结束NSString *strNew = [str substringFromIndex:2];// 从开始截取到索引处NSString *strNew2 = [str substringToIndex:3];// 字符串拼接NSString *strNew = [str stringByAppendingString:@"12班"];]// 格式化拼接NSString *strNew2 = [str stringByAppendingFormat:@"%d班",12];// 字符串替换NSString *strNew = [str stringByRepalcingOccurrencesOfString:@"上海"withString:@"传智"];// 判断字符串相等NSString *str1 = @"上海蓝鸥科技";BOOL result = [str isEqualToString:str1];// 判断前缀 后缀(应用场景 接收图片查看有无后缀)BOOL result1 = [str hasPrefix:@"上海"];BOOL result2 = [str hasSuffix:@"科技"];NSLog(@"%d %d",result1,result2);// 字符串比较NSString *str1 = @"adc";NSString *str2 = @"acc";// 返回值是个枚举: -1 0 1NSComparisonResult result = [str1 compare:str2]; //返回值是个枚举类型: -1,0,1 NSLog(@"%ld",result);// 字符串大小写转换NSString *str = @"how are you";NSString *strNew = [str uppercaseString];NSLog(@"%@",strNew); // 大写NSString *strNew2 = [strNew lowercaseString];     // 小写NSLog(@"%@",strNew2);NSString *strNew3 = [strNew2 capitalizedString];NSLog(@"%@",strNew3); // 首字母大写

2.不可变字符串 NSString
// 相当于指向常量区
// 不可变字符串 如果重新赋值的话 改变的不是其本身而是这个字符串 进行了重指向 指向了一个新的字符串
3.可变字符串 NSMutableString 初始化

NSMutableString *str = [[NSMutableString alloc] initWithString:@"sgr"];// 便利构造器方法NSMutableString *str1 = [NSMutableString stringWithString:@"sgr"];

以下操作特点:肯定是 没有返回值的,因为可变字符串操作的就是本身

[str appendString:@"wanglong"];// 插入字符[str insertString:@"da" atIndex:7];// 替换字符(范围替换)NSRange range = NSMakeRange(3, 1);[str replaceCharactersInRange:range withString:@"l"]; // 删除字符NSRange range1 = NSMakeRange(7, 2);[str deleteCharactersInRange:range1];NSLog(@"%@",str);