列表获取下一个元素或获取第一个元素

I want to get the next element in a list and if the list is at it's end I want the first element. So I just want it to circle in other words.

我想获取列表中的下一个元素,如果列表结束,我想要第一个元素。所以我只想用它来换句话说。

   List<int> agents = taskdal.GetOfficeAgents(Branches.aarhusBranch);
    if (lastAgentIDAarhus != -1)
    {
        int index = agents.IndexOf(lastAgentIDAarhus);
        if (agents.Count > index + 1)
        {
            lastAgentIDAarhus = agents[index + 1];
        }
        else
        {
            lastAgentIDAarhus = agents[0];
        }
    }
    else
    {
        lastAgentIDAarhus = agents[0];
    }

I am fairly displeased with my own solution shown above, let me know if you have a better one :)

我对上面显示的自己的解决方案感到非常不满,如果你有更好的解决方案,请告诉我:)

7 个解决方案

#1

lastAgentIDAarhus = agents[index == -1 ? 0 : index % agents.Count];

The use of the MOD operator % atuomatically chops the index to the range of possible indexes.

使用MOD运算符%atuomatically将索引切断到可能的索引范围。

The modulo operator is the compliment to the DIV (/) operator and returns the remainder of a division of two whole numbers. For example if you divide 9 by 6 the result is 1 with a remainder of 3. The MOD operator asks for the 3.

模运算符是对DIV(/)运算符的补充,并返回两个整数的除法的余数。例如,如果将9除以6,则结果为1,余数为3. MOD运算符要求3。

#2

Or simply:

public static T NextOf<T>(this IList<T> list, T item)
{
    var indexOf = list.IndexOf(item);
    return list[indexOf == list.Count - 1 ? 0 : indexOf + 1];
}

Example:

List<string> names = new List<string>();

names.Add("jonh");
names.Add("mary");

string name = String.Empty;    

name = names.NextOf(null);   //name == jonh

name = names.NextOf("jonh"); //name == mary

name = names.NextOf("mary"); //name == jonh

#3

As a slightly different take on this, here's an extension method you could use to make any IEnumerable 'circular'

对此略有不同,这里有一个扩展方法,你可以使用它来制作任何IEnumerable'循环'

  public static IEnumerable<T> AsCircularEnumerable<T>(this IEnumerable<T> enumerable)
  {
    var enumerator = enumerable.GetEnumerator();
    if(!enumerator.MoveNext())
      yield break;

    while (true)
    {
      yield return enumerator.Current;
      if(!enumerator.MoveNext())
        enumerator = enumerable.GetEnumerator();
    }
  }

so you could use that like this

所以你可以这样使用它

  var agents = new List<int> {1, 2, 3, 4, 123, 234, 345, 546};

  foreach(var i in agents.AsCircularEnumerable())
  {
    Console.WriteLine(i);
  }

Which will just keep going... :)

哪个会继续...... :)

#4

I like Vinicius's idea of using an extension method. Unfortunately the code he posted will throw an exception. This is based on his, but it will not throw an exception and it is very straightforward and easy to read (IMHO):

我喜欢Vinicius使用扩展方法的想法。不幸的是,他发布的代码会引发异常。这是基于他的,但它不会抛出异常,它非常简单易读(恕我直言):

public static T Next<T>(this IList<T> list, T item)
{
    var nextIndex = list.IndexOf(item) + 1;

    if (nextIndex == list.Count)
    {
        return list[0];
    }

    return list[nextIndex];
}

It will return the first item in the list if the item passed in is not in the list, since list.IndexOf(item) will return -1 in that case;

如果传入的项不在列表中,它将返回列表中的第一项,因为在这种情况下list.IndexOf(item)将返回-1;

#5

Not a great difference, but at least some less code (at least in the editor) ;o)

没有太大的区别,但至少有一些代码(至少在编辑器中); o)

List<int> agents = taskdal.GetOfficeAgents(Branches.aarhusBranch);
if (lastAgentIDAarhus != -1)
{
    int index = agents.IndexOf(lastAgentIDAarhus);
    lastAgentIDAarhus = (agents.Count > index + 1 ? agents[index + 1] : agents[0]); 
}
else
{
    lastAgentIDAarhus = agents[0];
}

#6

What do you think if we add some check to avoid common errors ?

如果我们添加一些检查以避免常见错误,您怎么看?

public static class ListExtensions
{
    public static TType Next<TType>(this IList<TType> list, TType item)
    {
        if (list == null) return default(TType);

        var itemIndex = list.IndexOf(item);
        if (itemIndex < 0) return list.FirstOrDefault();

        var nextIndex = itemIndex + 1;

        return nextIndex >= list.Count 
            ? list.FirstOrDefault() 
            : list[nextIndex];
    }
}

#7

string line = lines[lines.FindIndex(x => x.Contains(item)) + 1];

string line = lines [lines.FindIndex(x => x.Contains(item))+ 1];

#1

lastAgentIDAarhus = agents[index == -1 ? 0 : index % agents.Count];