Software Development

VB6 Tip: Adding controls to a form at runtime to increase flexibility

Adding controls to a form at runtime can give your VB6 program the flexibility to react to changing data and circumstances.

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In most Visual Basic 6 projects, the number of controls on a form are set at design time and don't change when the program runs. But what if you have a situation where the number of controls needed isn't known until runtime? For example, the program could read data from a database and need to display one control for each record that was found. This tip shows you how to add controls to a form at runtime. This technique is also applicable to essentially any Visual Basic control.

Add controls

To add controls at runtime, there must already be at least one instance of the control on the form, and it must be part of a control array. To create a control array containing only a single control, add the control to the form and then set its Index property to 0. This control doesn't have to be visible.

When the program runs, you add additional controls with the Load statement: Load ControlName(Index).

ControlName is the Name property of the control array you created and Index is the Index property of the new control. You should start at 1 because Index 0 is already taken by the control you placed on the form at design time.

Each control that you add in this way initially has the same properties as the original control. You'll have to change at least the Top and Left properties to prevent all the added controls from displaying at the same position onscreen.


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An example

The variable rs refers to a recordset that contains information about rooms in a dormitory. The code goes through the recordset and for each room, creates a Label control (lblRoom), and then a ListBox control (lstRoom). It then positions them in a grid on the form. ROOM_LIST_HEIGHT and ROOM_LIST_WIDTH are constants that specify the control size and are defined elsewhere.

col = 0
row = 0
Do While Not rs.EOF
    recordnumber = rs.AbsolutePosition
    Load lblRoom(recordnumber)
    lblRoom(recordnumber).Caption = "Room " & rs.Fields("RoomNumber").Value
    lblRoom(recordnumber).Top = row * (ROOM_LIST_HEIGHT * 1.3) + 300
    lblRoom(recordnumber).Left = col * (ROOM_LIST_WIDTH * 1.2) + 500
    lblRoom(recordnumber).Visible = True
    Load lstRoom(recordnumber)
    lstRoom(recordnumber).Left = lblRoom(recordnumber).Left
    lstRoom(recordnumber).Top = lblRoom(recordnumber).Top + _
        lblRoom(recordnumber).Height + 10
    lstRoom(recordnumber).Visible = True
    rs.MoveNext
    col = col + 1
    If col = 3 Then
        col = 0
        row = row + 1
    End If
Loop

Adding controls to a form at runtime can give your program the flexibility that's necessary to react to changing data and circumstances.

Peter Aitken has been programming with Visual Basic since Version 1.0. He has written numerous books and magazine articles on Visual Basic and other computer and programming topics.

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