OC中NSString 的常用方法 .

    NSString *str1 = @"BeiJing";
    NSString *str2 = @"beijing";
   
    //全部转为大写
    NSLog(@"%@",[str1 uppercaseString]);
   
    //全部转为小写
    NSLog(@"%@",[str1 lowercaseString]);
   
    //首字母大写
    NSLog(@"%@",[str1 capitalizedString]);
   
    //比较两个字符串内容是否相同
    BOOL b =[str1 isEqualToString:str2];
   
    //两个字符串内容比较
    //NSOrderedAscending    右边 > 左边
    //NSOrderedSame         内容相同
    //NSOrderedDescending   左边 > 右边
    NSComparisonResult result = [str1 compare:str2];
    if (result == NSOrderedAscending) {
        NSLog(@"右边 > 左边");
    }else if(result == NSOrderedSame){
        NSLog(@"内容相同");
    }else if (result == NSOrderedDescending){
        NSLog(@"左边 > 右边");
    }
   
    //忽略大小写进行比较，返回值与compare一样
    result = [str1 caseInsensitiveCompare:str2];
    if (result == NSOrderedAscending) {
        NSLog(@"右边 > 左边");
    }else if(result == NSOrderedSame){
        NSLog(@"内容相同");
    }else if (result == NSOrderedDescending){
        NSLog(@"左边 > 右边");
    }
   
    //判断字符串是否以指定字符串开头
    [str1 hasPrefix:@"aaa"];
    //判断字符串是否以指定字符串结尾
    [str1 hasSuffix:@"aaa"];
   
    //判断字符串是否包含指定字符串，返回位置和长度
    NSRange range = [@"123456" rangeOfString:@"456"];
    NSLog(@"%@", NSStringFromRange(range));
   
    //反向搜索
    range = [@"123456456qweasasd456" rangeOfString:@"456" options:NSBackwardsSearch];
    NSLog(@"%@",NSStringFromRange(range));
   
    //指定范围进行搜索
    range = NSMakeRange(0, 9);
    range = [@"123456456qweasasd456" rangeOfString:@"456" options:NSBackwardsSearch range:range];
    NSLog(@"%@",NSStringFromRange(range));

 NSString *str = @"123456789";
        NSLog(@"%@",[str substringFromIndex:3]);
        NSLog(@"%@",[str substringToIndex:6]);
        NSLog(@"%@",[str substringWithRange:NSMakeRange(3, 3)]);
       
        //用指定字符串分割字符串，返回一个数组
        NSArray *array = [@"1,2,3,4,5,6" componentsSeparatedByString:@","];
        NSLog(@"%@",array);
       
        //将数组中的字符串组合成一个文件路径
        NSMutableArray *components = [NSMutableArray array];
        [components addObject:@"Users"];
        [components addObject:@"CentralPerk"];
        [components addObject:@"Desktop"];
        NSString *path = [NSString pathWithComponents:components];
        NSLog(@"%@",path);  //Users/CentralPerk/Desktop
       
        //将一个路径分割成一个数组
        NSArray *array1 = [path pathComponents];
        NSLog(@"%@",array1);
       
        //判断是否为绝对路径(依据：是否以'/'开始)
        path = @"/Users/CentralPerk/Desktop";
        NSLog(@"%i",[path isAbsolutePath]);
       
        //获取最后一个目录
        NSLog(@"%@",[path lastPathComponent]);
       
        //删除最后一个目录
        NSLog(@"%@",[path stringByDeletingLastPathComponent]);
       
        //拼接一个目录
        NSLog(@"%@",[path stringByAppendingPathComponent:@"aaa"]);   ///Users/CentralPerk/Desktop/aaa
        NSLog(@"%@",[path stringByAppendingString:@"aaa"]);      ///Users/CentralPerk/Desktopaaa
        NSLog(@"%@",[path stringByAppendingFormat:@"%@%@",@"b",@"c"]);  ///Users/CentralPerk/Desktopbc
       
        //拓展名出来
        //获取拓展名,不带.
        NSString *str2 = @"Users/CentralPerk/Desktop/test.txt";
        NSLog(@"%@",[str2 pathExtension]);
        //添加拓展名,不需要带.
        NSLog(@"%@",[str2 stringByAppendingPathExtension:@"mp3"]);
        //删除拓展名,带.一块删除
        NSLog(@"%@",[str2 stringByDeletingPathExtension]);
       
        //字符串转为 int double float
        NSString *str3 = @"123";
        NSLog(@"%i",[str3 intValue]);
        NSLog(@"%zi",[str3 length]);
       
        //取出指定位置的字符
        unichar c = [str3 characterAtIndex:2];
        NSLog(@"%c",c);
       
        //转为C语言的字符串
        const char *s = [str3 UTF8String];
        NSLog(@"%s",s);

  

// trim

NSString *str = @"  abcd   ";
NSString *str2 = [str stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
NSLog(@"%@",str);
NSLog(@"%@",str2);