Populate TreeView with arbitrary depth from DataTable

Question

I have a DataTable with id, parent, label columns and want to populate a TreeView with it.

I'm new to c# and as far as I understand, there is no ready solution for it, unlike some other languages.

So I sorted the data hierarchically at DataTable level and wrote not a very pretty recursive method.

Is this a good solution or can it be greatly improved?

 using System.Data;
 public void Populate()
 {
 //data example
 var table = new DataTable();
 DataColumn column;
 DataRow row;
 column = new DataColumn(); column.DataType = Type.GetType("System.Int32"); column.ColumnName = "id"; table.Columns.Add(column);
 column = new DataColumn(); column.DataType = Type.GetType("System.Int32"); column.ColumnName = "parent"; table.Columns.Add(column);
 column = new DataColumn(); column.DataType = Type.GetType("System.String"); column.ColumnName = "label"; table.Columns.Add(column);
 row = table.NewRow(); row["id"] = 1; row["parent"] = DBNull.Value; row["label"] = "root1"; table.Rows.Add(row);
 row = table.NewRow(); row["id"] = 2; row["parent"] = 1; row["label"] = "child11"; table.Rows.Add(row);
 row = table.NewRow(); row["id"] = 3; row["parent"] = 1; row["label"] = "child12"; table.Rows.Add(row);
 row = table.NewRow(); row["id"] = 4; row["parent"] = DBNull.Value; row["label"] = "root2"; table.Rows.Add(row);
 row = table.NewRow(); row["id"] = 5; row["parent"] = 4; row["label"] = "child21"; table.Rows.Add(row);
 row = table.NewRow(); row["id"] = 6; row["parent"] = 5; row["label"] = "child211"; table.Rows.Add(row);
 // call method
 int i = 0;
 var result = new List<TreeNode>();
 var data = table.Rows;
 PopTree(ref data, DBNull.Value, ref i, ref result);
 treeView1.Nodes.AddRange(result.ToArray());
 }
 private void PopTree(ref DataRowCollection data, object parent, ref int i, ref List<TreeNode> result)
 {
 if (i >= data.Count || data[i]["parent"].ToString() != parent.ToString())
 {
 return;
 }
 var row = data[i];
 var children = new List<TreeNode>();
 i++;
 if (i < data.Count && row["id"].ToString() == data[i]["parent"].ToString())
 {
 PopTree(ref data, row["id"], ref i, ref children);
 }
 TreeNode node = new TreeNode(row["label"].ToString(), children.ToArray());
 result.Add(node);
 PopTree(ref data, parent, ref i, ref result);
 }

• radarbob: ... or can it be greatly improved? That is a much more open question than you may realize. Perhaps read this SO thread for starters: Tree Data Structure in C#

Answer 1

Let me focus only on the Populate function in this post.

Defining Columns

You can define columns in a really concise way thanks to the AddRange method of the DataColumnCollection class

table.Columns.AddRange(new[] {
 new DataColumn("id", typeof(int)),
 new DataColumn("parent", typeof(int)), 
 new DataColumn("label", typeof(string)),
});

I would also advice to use typeof operator over Type.GetType

• since the former can give you compile time safety
• whereas the latter can fail at runtime in case of a typo for example.

Populating Rows with data

Unfortunately DataRowCollection does not define an AddRange method so, you have to add the rows one-by one. Here the preferred approach is to define the data separately from the DataRow population.

Here I have created an array of ValueTuples to represent only the data.

var relationships = new (int Id, int? Parent, string Label)[] {
 (1, null, "root1"),
 (2, 1, "child11"),
 (3, 1, "child12"),
 (4, null, "root2"),
 (5, 4, "child21"),
 (6, 5, "child211"),
};

Finally here is a foreach to convert the data into a DataRow then add it to the DataTable

foreach (var relationship in relationships)
{
 var row = table.NewRow();
 row[0] = relationship.Id;
 if (relationship.Parent.HasValue)
 row[1] = relationship.Parent;
 else
 row[1] = DBNull.Value;
 row[2] = relationship.Label;
 table.Rows.Add(row);
}

• phoog: It seems from the question text that the asker is interested in the PopTree algorithm and the Populate method is provided for the sake of having a working example. The advice in this answer is sound, but it seems not to answer the question.
• Peter Csala: @phoog Yes that's right the question is more about the PopTree. But that Populate code was shouting for improvement :)
• phoog: That is certainly true.