C＃返回类数组中单个变量的数组

Question

This may seem like a silly question but it's something I've never found an answer to.

If I had an array of a class:

public class Folder
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public Folder[] folders = new Folder[] {};

Is there a way to return all instances of ID without looping through and collecting them all?

If there isn't, what would you consider to be the best way of doing it so that I had an array of integers?

Thanks in advance,

SumGuy

ps If anyone can come up with a more appropriate title to this question that would be appreciated as well

Answer 1

You would have to loop through them some time in order to get a list of the Ids

You can get an array of Ids this way:

int[] Ids = folders.Select(f => f.Id).ToArray();

(Must be using .NET 3.5 or above - the above performs the loop internally, so it is still looping)

Answer 2

public class Folder 
{     
    public int Id { get; set; }     
    public string Name { get; set; } }  

    // Try to avoid exposing data structure implementations publicly
    private Folder[] _folders = new Folder[] {};  

    public IEnumerable<Folder> Folders 
    {
        get 
        {
            return this._folders;
        }
    }

    public IEnumerable<int> FolderIds 
    {
        get 
        {
            // Linq knows all
            return this._folders.Select(f => f.Id);
        }
    }
}