Instant Change Scroll Hangs with Modal Show in Changing Event

ID Number: Q84067

1.00

WINDOWS

buglist1.00

Summary:

Unpredictable results can occur when you try to call or show a modal

form or window from the Instant Change Scroll custom control Changing

event procedure. Doing a show of a modal form or even using a dialog

box function such as InputBox$ can cause an Unrecoverable Application

Error (UAE) or even a system hang if called from the Changing event

procedure.

Showing a modal dialog box or modal form in a change event of any type

of scroll bar is an improper programming practice, and will lead to

unpredictable results.

This information applies to the INSTSCRL.VBX custom control supplied

with Microsoft Professional Toolkit for Microsoft Visual Basic

programming system version 1.0 for Windows.

More Information:

Below are some examples of using the InputBox$ function from within

the Changing event procedures for both the horizontal and vertical

Instant Change Scroll Bar controls.

Steps to Reproduce Problem

--------------------------

1. Run Visual Basic, or from the File menu, choose New Project (ALT,

F, N) if Visual Basic is already running. Form1 is created by

default.

2. From the File menu, choose Add File. In the Files box, select the

INSTSCRL.VBX custom control file. The Instant Change Scroll Bar

tools will appear in the Toolbox.

3. Place either an InstVScroll or InstHScroll control on Form1.

4. Add the following code to the InstHScroll1_Changing event

procedure:

Sub InstHScroll_Changing ( )

a$ = InputBox$("hello")

End Sub

-or-

Sub InstVScroll_Changing ( )

a$ = InputBox$("hello")

End Sub

5. Press F5 to run the program.

The machine may either hang or return a UAE.

Additional reference words: 1.00