Creating Tree Views in Code

You can create tree views in code as well as at design time. To see an example, take a look at the CreateTreeView program on the CD-ROM—this example creates a tree view of employees, each of whom has several sales account nodes.

The trick here is realizing that the hierarchical nature of tree views means that one node's Nodes collection can contain child nodes, which can itself contain child nodes, and so on, so you can refer to nodes using syntax like MyNode.Nodes(3). Nodes(5). To add a new node, you use the Nodes collection's Add method. Like other controls, you can use the BeginUpdate and EndUpdate methods to turn off updating of the tree view while you're updating it. Note that this example uses the Clear method to clear all nodes in the tree view before refilling it. (Note also that I'm using a few advanced programming techniques here, such as creating our own classes and storing objects in an ArrayList collection, which we'll see soon in the book.) Here's the code, showing how to stock a tree view with nodes, and how to give those nodes child nodes, and so on, at run time:

Public Class Form1
    Inherits System.Windows.Forms.Form

    'Windows Form Designer generated code

    Private EmployeeArray As New ArrayList()

    Private Sub Button1_Click(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles Button1.Click
        Dim intLoopIndex As Integer
        For intLoopIndex = 0 To 9
            EmployeeArray.Add(New Employee("Employee " & _
                intLoopIndex.ToString()))
        Next intLoopIndex

        Dim EmployeeObject As Employee
        For Each EmployeeObject In EmployeeArray
            For intLoopIndex = 0 To 3
                EmployeeObject.EmployeeAccounts.Add(New _
                    Account("Account " & intLoopIndex.ToString()))
            Next intLoopIndex
        Next EmployeeObject

        TreeView1.BeginUpdate()
        TreeView1.Nodes.Clear()

        Dim RootNode = New TreeNode("Employees")
        TreeView1.Nodes.Add(RootNode)

        For Each EmployeeObject In EmployeeArray
            TreeView1.Nodes(0).Nodes.Add(New _
                TreeNode(EmployeeObject.EmployeeName))

            Dim AccountObject As Account
            For Each AccountObject In EmployeeObject.EmployeeAccounts
                TreeView1.Nodes(0).Nodes(_
                    EmployeeArray.IndexOf(EmployeeObject)).Nodes.Add(_
                    New TreeNode(AccountObject.AccountID))
            Next AccountObject
        Next EmployeeObject

        TreeView1.EndUpdate()
    End Sub
End Class

Public Class Employee
    Private Index = 0
    Public EmployeeName As String
    Public EmployeeAccounts As New ArrayList()

    Public Sub New(ByVal Name As String)
        EmployeeName = Name
    End Sub
End Class

Public Class Account
    Public AccountID As String
    Public Sub New(ByVal ID As String)
        AccountID = ID
    End Sub
End Class

You can see the results in Figure 10.13; when you click the "Create tree view" button, the code creates the display you see in that figure.

Figure 10.13: Creating a tree view in code.