Populate a TreeView Control C#

August 27, 2009 by Christoff Truter C#  

Populating a TreeView control in a windows application using SQL and C# is quite straightforward.

Create a self referencing table, lets call it myTable, quite orginal don't you think? ;)

CREATE TABLE [dbo].[myTable](
	[ID] [int] IDENTITY(1,1) NOT NULL,
	[title] [varchar](255) NOT NULL,
	[parentID] [int] NULL,
 CONSTRAINT [PK_myTable] PRIMARY KEY CLUSTERED 
(
	[ID] ASC
)WITH (PAD_INDEX  = OFF, IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]

Insert some hierarchal data.

SET IDENTITY_INSERT myTable ON
GO

INSERT INTO myTable(ID, title, parentID) VALUES(1,'Microsoft', NULL)
INSERT INTO myTable(ID, title, parentID) VALUES(2,'C#', 1)
INSERT INTO myTable(ID, title, parentID) VALUES(3,'VB.net', 1)
INSERT INTO myTable(ID, title, parentID) VALUES(4,'Open Source', NULL)
INSERT INTO myTable(ID, title, parentID) VALUES(5,'Python',	4)
INSERT INTO myTable(ID, title, parentID) VALUES(6,'Ruby', 4)
INSERT INTO myTable(ID, title, parentID) VALUES(7,'PHP', 4)
INSERT INTO myTable(ID, title, parentID) VALUES(8,'Perl', 4)
INSERT INTO myTable(ID, title, parentID) VALUES(9,'Java', 4)
INSERT INTO myTable(ID, title, parentID) VALUES(10,'LinQ', 2)
INSERT INTO myTable(ID, title, parentID) VALUES(11,'5.2', 7)
INSERT INTO myTable(ID, title, parentID) VALUES(12,'4.4', 7)

GO
SET IDENTITY_INSERT myTable OFF
GO

I assume in my code example that the root parent node equals 0, hence when returning results from SQL like in the stored procedure, I use the ISNULL method to return 0 from a NULL.

You can just define a root value as well...

CREATE PROCEDURE viewMyTable
AS
BEGIN
	SELECT ID, title, ISNULL(parentID, 0) AS parentID
	FROM myTable
END

Add a same table key contraint.

ALTER TABLE [dbo].[myTable]  WITH CHECK ADD  CONSTRAINT [FK_myTable_myTable] FOREIGN KEY([parentID])
REFERENCES [dbo].[myTable] ([ID])
GO
ALTER TABLE [dbo].[myTable] CHECK CONSTRAINT [FK_myTable_myTable]

• In your windows application, drag and drop a treeview control onto your form.
• Populate a DataTable with your stored procedure.

Pass your TreeNodeCollection, the parentID you wish to start with and DataTable to the following method: eg. PopulateTreeView(SomeTreeView.Nodes, 0, SomeDataTable);

protected void PopulateTreeView (TreeNodeCollection parentNode, int parentID, DataTable folders)
{   
    foreach (DataRow folder in folders.Rows)
    {
        if (Convert.ToInt32(folder["parentID"]) == parentID)
        {
            String key = folder["ID"].ToString();
            String text = folder["title"].ToString();
            TreeNodeCollection newParentNode = parentNode.Add(key, text).Nodes;
            PopulateTreeView(newParentNode, Convert.ToInt32(folder["ID"]), folders);                    
        }
    }
}

If everything went according to plan, you'll end up with something like this: