DOCUMENT:Q178490  11-JAN-2001  [vbwin]
TITLE   :PRB: "Can't Assign To Read-Only Property" Error Message
PRODUCT :Microsoft Visual Basic for Windows
PROD/VER:
OPER/SYS:
KEYWORDS:kbGrpDSVB

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The information in this article applies to:

 - Microsoft Visual Basic Learning Edition for Windows, versions 5.0, 6.0 
 - Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0 
 - Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0 
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SYMPTOMS
========

You receive the following error when you attempt to programmatically set a
control property:

   Compile Error:
   Can't assign to read-only property

CAUSE
=====

You are attempting to programmatically change a read-only property of a control
at run-time.

RESOLUTION
==========

If you need to change a read-only property at run-time, create another copy of
the control and set the read-only property at design-time. Then, display the
copy of the control THAT is appropriate to your task.

STATUS
======

This behavior is by design.

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.

REFERENCES
==========

"Can't make an assignment to a read-only property" topic in the Visual Basic
Online Reference

(c) Microsoft Corporation 1997. All Rights Reserved. Contributions by Arsenio
Locsin, Microsoft Corporation


Additional query words: kbVBp500 kbVBp600 kbVBp kbdsd kbDSupport kbControl read only run time design time runtime readonly

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Keywords          : kbGrpDSVB 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500 kbVBA600 kbVB500 kbVB600
Issue type        : kbprb

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