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). I

Answer 1

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):

/// 
The employee structure with explicit conversion to a TreeNode (you may also use implicit conversion, but i prefer explicit).
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
{
    /// 
More abstract and readable way to add an employee.
    public static void Add(this Dictionary> employees, int id, string name, int bossId)
    {
        if (!employees.ContainsKey(bossId)) employees[bossId] = new List();

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

The method used to populate a TreeView:

public static void PopulateTreeView(Dictionary> 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> employees = new Dictionary>();

/* 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.