PRB: "Can't Assign To Read-Only Property" Error Message (178490)

MORE INFORMATION

Controls can have properties that can only be set during design-time. For example, the Style property of a Combo box control can only be changed at design-time. Properties are usually read-only at run-time because the style is inherent to the window created by the control. Control developers call this a "pre-hWnd" property.

The following section demonstrates how you can simulate changing a read- only property of a control at run-time. In this example, a control array of three combo boxes is used. Each member of the combo box array has a different style property. When you click a command button, one member of the combo box array is displayed and the other two members are hidden.

Step-by-Step Example

1. Start a new Standard EXE project in Visual Basic. Form1 is created by default.
2. Add a CommandButton, a label control, and an array of three combo boxes to Form1. Set the following properties for the combo box controls:

      Control           Default Name     Property        Setting
      --------------------------------------------------------------------
      ComboBox          Combo1(0)        Style           0-DropDown Combo
      ComboBox          Combo2(1)        Style           1-Simple Combo
      ComboBox          Combo3(2)        Style           2-Dropdown List
   						

3. Copy the following code to the Code window of Form1 form:

         Option Explicit
   
         Dim bytCount As Byte
         Dim captions(0 To 2) As String
   
         Private Sub Form_Load()
            Dim i As Integer
            bytCount = 0
            Command1.Caption = "Change Style"
            captions(0) = "Dropdown Combo"
            captions(1) = "Simple Combo"
            captions(2) = "Dropdown List"
            Label1.AutoSize = True
            For i = 0 To 2
               With Combo1(i)
                     .Left = 2400
                     .Top = 360
                     .Visible = False
               End With
            Next i
            Label1.Caption = captions(bytCount)
            Combo1(bytCount).Visible = True
            Combo1(1).Height = 2000
            For i = 1 To 10
               Combo1(0).AddItem i
               Combo1(1).AddItem i
               Combo1(2).AddItem i
            Next i
         End Sub
   
         Private Sub Command1_Click()
            Combo1(bytCount).Visible = False
            bytCount = (bytCount + 1) Mod 3
            Combo1(bytCount).Visible = True
            Label1.Caption = captions(bytCount)
         End Sub
   						

4. On the Run menu, click Start, or press the F5 key to start the program. Click on a CommandButton to change the style.