将元素添加到列表的递归方法

Question

I would like to get the list of all sub-directories of a folder, including the nested ones.
Therefore, I would like to have a list<Folder> myList that will be filled by a recursive method.

 void myMethod(?)  
 {
   list<Folder> listFolders = ...  ;
   foreach (Folder curFolder in listFolders)
      {
        myList.add(curFolder);
      }
 }

Is it possible?

Answer 1

Declare a function like this

List<Folder> ListFolders(Folder initialFolder)
{
    var folders = new List<Folder>();
    folder.Add(initialFolder);
    foreach (var f in initialFolder.GetSubFolders())
    {
        folders.AddRange(ListFolders(f));
    }
    return folders;
}

The Folder class is left to you as an exercice, it will have to contain the name of the current folder, and a method to get its subfolders (hint: look into the System.IO.Directory class)

Answer 2

The following is an extension method that selects from an IEnumerable Recursively:

    public static IEnumerable<T> SelectRecursive<T>(this IEnumerable<T> source, Func<T, IEnumerable<T>> recursiveSelector)
        {
            foreach (var i in source)
            {
                yield return i;

                var directChildren = recursiveSelector(i);
                var allChildren = SelectRecursive(directChildren, recursiveSelector);

                foreach (var c in allChildren)
                {
                    yield return c;
                }
            }
        }

You can use it to create a "flat" enumerable out of every hierarchy. Assume the Folder class has a property that returns its direct children: as follows:

public class Folder 
{
    public IEnumerable<Folder> Children {get;}
}

You will be able to get a flat list of sub folders with the following line:

var flatList = folder.SelectRecursive(f => f.Children).ToList();

Hope that this is what you mean.

Answer 3

    static void Main(string[] args)
    {
            List<string> dirs = new List<string>();
            addDirectoryToList(@"C:\exampledir\", dirs);
    }

    void addDirectoryToList(string dir, List<string> list)
    {
        DirectoryInfo dirInfo = new DirectoryInfo(dir);
        foreach (DirectoryInfo subdir in dirInfo.GetDirectories())
        {
            addDirectoryToList(subdir.FullName, list);
        }
    }

or without recursion:

    void addDirectoryToList(string dir, List<string> list)
    {
        DirectoryInfo dirInfo = new DirectoryInfo(dir);
        list.Add(dir);
        foreach (DirectoryInfo subdir in dirInfo.GetDirectories("*", SearchOption.AllDirectories))
        {
            list.Add(subdir.FullName);
        }
    }