how to populate treeview?

Question

I have a table "Category".It is simply a table of users, where each are identified with a unique UserId and have a corresponding ParentId (pointing to their boss' UserId). If it's a top-level user, then the ParentId is set to 0. Can someone please help me figure out the best way to populate this list in a tree view?

Answer 1

If you mean WinForms treeview I would do something like this (error checking skipped):

private void FillTreeView(object sender, EventArgs e)
{
    // create fake datatable
    DataTable dt = new DataTable();
    dt.Columns.Add("UserId",typeof(int));
    dt.Columns.Add("Name",typeof(string));
    dt.Columns.Add("ParentId", typeof(int));


    dt.Rows.Add(new object[] { 3, "Level_1_A", 2 });
    dt.Rows.Add(new object[] { 4, "Level_1_B", 2 });
    dt.Rows.Add(new object[] { 2, "Level_0_A", 0 });
    dt.Rows.Add(new object[] { 5, "Level_2_A", 3 });
    dt.Rows.Add(new object[] { 6, "Level_2_B", 3 });
    dt.Rows.Add(new object[] { 7, "Level_0_B", 0 });
    dt.Rows.Add(new object[] { 8, "Level_1_C", 7 });

    // call recursive function
    AddCurrentChild(0, dt, treeView1.Nodes);
}

private static void AddCurrentChild(int parentId, DataTable dt, TreeNodeCollection nodes)
{
    var rows = dt.Select("ParentId = " + parentId);
    foreach (var row in rows)
    {
        var userId = (int) row["UserId"];
        var name = row["Name"] as string;

        var node = nodes.Add(userId.ToString(), name.ToString());
        node.Tag = row; // if you need to keep a row reference on the node
        AddCurrentChild(userId, dt, node.Nodes);
    }
}

Answer 2

I guess you know how to read data from database so I skip that part.

An abstract version - you could read the employees from any source.

Some helper entities (you can do without them ofc - it is just easier/nicer to use this way):

/// <summary>The employee structure with explicit conversion to a TreeNode (you may also use implicit conversion, but i prefer explicit).</summary>
public struct Employee
{
    public int Id;
    public string Name;
    public int BossId;

    public static explicit operator TreeNode(Employee e) { return new TreeNode(e.Name); }
}

public static class EmployeesExtension
{
    /// <summary>More abstract and readable way to add an employee.</summary>
    public static void Add(this Dictionary<int, List<Employee>> employees, int id, string name, int bossId)
    {
        if (!employees.ContainsKey(bossId)) employees[bossId] = new List<Employee>();

        employees[bossId].Add(new Employee() { Id = id, Name = name, BossId = bossId });
    }
}

The method used to populate a TreeView:

public static void PopulateTreeView(Dictionary<int, List<Employee>> employees, int bossId, TreeNodeCollection nodes)
{
    if (!employees.ContainsKey(bossId)) return;

    foreach (Employee e in employees[bossId])
    {
        TreeNode tn = (TreeNode)e;
        nodes.Add(tn);
        PopulateTreeView(employees, e.Id, tn.Nodes);
    }
}

How to use it in your code:

Dictionary<int, List<Employee>> employees = new Dictionary<int, List<Employee>>();

/* Here you will do the actual reading from DB */
//             id,        name,      bossId
employees.Add(666, "The Master     ", 0);
employees.Add(123, "The Underling 1", 666);
employees.Add(879, "The Underling 2", 666);
employees.Add(001, "The Slave 1    ", 123);

this.treeView1.BeginUpdate();
PopulateTreeView(employees, 0, this.treeView1.Nodes);
this.treeView1.EndUpdate();

Using the BeginUpdate / EndUpdate methods will eliminate the "blinking" of your GUI.

Answer 3

Just posted something similar on another post: Adding child nodes to tree view based on single database table with parent/child links