Make tree structure from list of objects in c#

Question

I have a class called Detail as given below:

public class Detail
{
    public int Id { get; set; }
    public string Name { get; set; }
    public System.Nullable<int> ParentID { get; set; }
}

And I make a list of detail as given below:

        List<Detail> Details= new List<Detail>();

        Details.Add(new Detail { Id = 1, Name = "James", ParentID =null });
        Details.Add(new Detail { Id = 2, Name = "David", ParentID = 1 });
        Details.Add(new Detail { Id = 3, Name = "Richard", ParentID = 2 });
        Details.Add(new Detail { Id = 4, Name = "John", ParentID = 3 });
        Details.Add(new Detail { Id = 5, Name = "Robert", ParentID = 3 });
        Details.Add(new Detail { Id = 6, Name = "Paul", ParentID = 3 });
        Details.Add(new Detail { Id = 7, Name = "Kevin", ParentID = 2 });
        Details.Add(new Detail { Id = 8, Name = "Jason", ParentID = 7 });
        Details.Add(new Detail { Id = 9, Name = "Mark", ParentID = 7 });
        Details.Add(new Detail { Id = 10, Name = "Thomas", ParentID = 9 });
        Details.Add(new Detail { Id = 11, Name = "Donald", ParentID = 9 });

And now I want this Detail list convert into tree structure.

Please be more specific on the tree structure, how do you imagine the nodes being linked together? By this I mean, what criteria will determine which node is linked to which? — Trev Davies
– Trev Davies, Commented Apr 1, 2016 at 7:26
@Remuze I edited it. Please check it again. Its a detail only — devendra
– devendra, Commented Apr 1, 2016 at 7:28
@Remuze The ParentID will determine the parent node. Thats how they will link together — devendra
– devendra, Commented Apr 1, 2016 at 7:33
I think you will find information here including an example: stackoverflow.com/questions/66893/… — Trev Davies
– Trev Davies, Commented Apr 1, 2016 at 7:41
Could you simply use a Detail instead of an int to specify the parent? Otherwise this can help you — Matteo Umili
– Matteo Umili, Commented Apr 1, 2016 at 7:44

Captain0 · Accepted Answer · 2016-04-01 07:46:29Z

4

You can try the following

Add a new class to hold the tree object

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

  public TreeNode Parent { get; set; }
  public List<TreeNode> Children{ get; set; }
}

Then add a recursive method to build the tree

private static List<TreeNode> FillRecursive(List<Detail> flatObjects, int? parentId=null)
{
  return flatObjects.Where(x => x.ParentID.Equals(parentId)).Select(item => new TreeNode
  {
    Name = item.Name, 
    Id = item.Id, 
    Children = FillRecursive(flatObjects, item.Id)
  }).ToList();
}

Then call it where you need it

 var tree = FillRecursive(Details,null);

answered Apr 1, 2016 at 7:46

Captain0

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3 Comments

ironstone13 Over a year ago

I think FillRecursive does not set the TreeNode.Parent, I would say it is sufficient to have either Parent or Children property in TreeNode Also FillRecursive does not terminate on invalid input, for example {id=1,ParentId=2}, {id=2,ParentId=1}

devendra Over a year ago

@ironstone13 is there any better option?

ironstone13 Over a year ago

@devendra - it depends on whether you need the reference to Parent node (how will you traverse the tree) and whether you expect inconsistent data in your input list

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