Read-only Edit Boxes (Functions/Subroutines/Programs)

Introduction

The edit box control has a check-box for "Read Only" in Form Design mode. This article describes how to toggle the read-only attribute at run-time.

Invisible, Disabled, and Read-Only

There are three simple ways to keep the user from editing data that is in a control on a form. Each has a different purpose:

Invisible	Not showing the control implies is a visual clue that the user shouldn't be able to see or update the data. For example, sensitive information in a secure system.
Disabled	Disabling the control is a visual clue that the data in the control is somehow unapplicable to the present state of the form. For example, the Position, Width, and Height details on the first tab of the Popup Designer.
Read-Only	Read-only is not a visual clue; the user can only tell that it is read-only when they start typing and nothing happens. The implication of read-only is that the data is the result of a calculation (and therefore can't be updated) or that the user is not supposed to be able to change the information, but is supposed to be able to read the information, scroll through the information, etc.

The problem with disabling an edit box is that it does not allow the edit box to be scrolled. Setting the edit box to read-only instead of disabled allows the user to scroll horizontally and vertically using the auto-scroll feature or the scroll bars. The user can also select text and copy text to the clip-board.

Implementing Read-Only Edit Boxes

The following function can be used to toggle the read-only setting of an edit box:

function SetReadOnly(CtrlEntID, ReadOnly)

declare function Get_Property

declare subroutine SendMessage

$insert Logical

$insert PS_Equates

$insert Ctrl_Property_Equates

equ WM_USER$ to 1024

equ EM_SETREADONLY$ to WM_USER$ + 31

if assigned(CtrlEntID) else

return FALSE$

end

Handle = Get_Property(CtrlEntID, HANDLE$)

if Handle else

return FALSE$

end

* default read-only to true

* (assume if it isn't passed that the user is setting the

* control to read-only, as implied by the function name)

if assigned(ReadOnly) else

ReadOnly = ""

end

if len(ReadOnly) then

* efficient way to make sure that ReadOnly is boolean

ReadOnly = not(not(ReadOnly))

end else

ReadOnly = TRUE$

end

Type = Get_Property(CtrlEntID, TYPE$)

begin case

case Type = PSCTL_EDITBOX$

* use the Windows SendMessage function to toggle the read-only

* state of the edit box

SendMessage(Handle, EM_SETREADONLY$, ReadOnly, 0)

* read-only processing for other controls could be placed here

* case Type = …

case OTHERWISE$

return FALSE$

end case

return TRUE$

Using the SetReadOnly Function

The following form, which has no code on it, shows how to use the SetReadOnly function:

Place an edit box on a new form, and set the name to EDITBOX_1 (which is the default name for the first edit box). Then place two buttons on the form. The first, titled "Read-Only", has the following Quick-Event: