遍历NSString每一个字符的正确方式

贴代码：

- (void)compare2{
    
    NSString *theString = @"a👌3👌";
    NSLog(@"theString--->%@",theString);
    
    //方法一(错误，emoji不打印)
    for (int i = 0; i < theString.length; i++) {
        unichar ch = [theString characterAtIndex:i];
        NSString *everyString = [NSString stringWithCharacters:&ch length:1];
        NSLog(@"everyString--->%@",everyString);
    }
    //打印：
    /*
     everyString--->a
     everyString--->3
     */
    
    
    //方法二(错误，emoji打印2次)
    NSRange range ;
    NSRange stringRange = [theString rangeOfString:theString];// log：location=0, length=6
    for (int i = 0; i < theString.length; i++) {
        range = [theString rangeOfComposedCharacterSequenceAtIndex:i];
        NSString *everyString = [theString substringWithRange:range];
        NSLog(@"everyString--->%@",everyString);
    }
    //打印：
    /*
    everyString--->a
    everyString--->👌
    everyString--->👌
    everyString--->3
    everyString--->👌
    everyString--->👌
     */
    
    
    
    //方法三(正确，可打印emoji)
    for(int i=0; i<theString.length; i+=range.length){
        range = [theString rangeOfComposedCharacterSequenceAtIndex:i];
        NSString *s = [theString substringWithRange:range];
        NSLog(@"s--->%@",s);
    }
    //打印：
    /*
     s--->a
     s--->👌
     s--->3
     s--->👌
     */
    
    
    
}

方法二和三区别在于：i++ 和 i+=range.length
emoji表情占两个字符位置

参考文章：
https://www.douban.com/note/299691317/