Q136070: DOC: Incorrect Examples on Pages 69-75 of Developer’s Guide

Article: Q136070
Product(s): Microsoft FoxPro
Version(s): WINDOWS:3.0,3.0b
Operating System(s): 
Keyword(s): kbdocfix kbvfp
Last Modified: 07-JAN-2000

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, versions 3.0, 3.0b 
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SUMMARY
=======

The example that create a VCR control in the Visual FoxPro "Developer's Guide"
on pages 69-75 creates a subclass of the VCR control. When an instance of VCR2
is created on a form, the container is not sized correctly; it is much wider
than the form.

The following conditions lead to this problem:

- The ScaleMode of the form is in foxels.

- The width of the VCR2 container, expressed in foxels, is decimal.

- The width of the VCR2 container is used as a variable in the body of the
  class definition (in the DEFINE part). In this example, the specific lines
  are:

  Left=This.Width+.2
  Width=This.Width+This.CmdQuit.Width+.2

If all these conditions are true, then when an instance of the class is created,
Visual FoxPro sees that the width of the container is in foxels. It converts the
number to pixels, using the font of the form as the basis for conversion. That
number is in turn used to size the container on the form, but it is not
converted back to foxels. In this example, the Width of the container is
converted from 6.2 foxels to 61 pixels. When the container is placed on the
form, the same measure is used. However, the unit is no longer pixels, it is
foxels. So the width of the container is 61 foxels.

Fix Status
----------

This documentation error has been fixed in Visual FoxPro 5.0 for Windows.

MORE INFORMATION
================

To work around this problem, ensure that one of the conditions listed in the
"Cause" section of this article is not met. In particular:

- You can use the pixel unit instead of foxels to dimension the form and the
  object it contains. This way, pixel is the default scale unit, so no
  conversion occurs.

  -or-

- If the value of a property depends on another member variable, do not define
  this property in the body of the class. You can use Init event handler for
  this purpose.

Using the second alternative, the following definition of the VCR2 class ensures
that the width of the VCR2 container is correct:

     DEFINE CLASS vcr2 as vcr
     ADD OBJECT cmdQuit AS COMMANDBUTTON WITH ;
        Caption="Quit", ;
        Height=2, ;
        Width=6.8

     PROCEDURE INIT
     This.CmdQuit.Left=This.Width+.2
     This.Width=This.Width+This.CmdQuit.Width+.2
     ENDPROC

     PROCEDURE cmdQuit.CLICK
       Release Thisform
     ENDPROC

     ENDDEFINE

In addition to the problem listed above, the example contains another inaccuracy
that should not affect your form. Pages 69 and 71 define the Scalemode property
as a property of a CommandButton and a Container. However, the Scalemode
property applies to forms and toolbars only. It does not apply to control or
container objects.

REFERENCES
==========

For more information about foxels and pixels, please see the following articles
in the Microsoft Knowledge Base:

  Q106161 How to Convert Screen Object Positions Between Platforms

  Q129208 Pixel Replaces Foxel as Default Scale Value in Design Mode


Additional query words: docerr navigation buttons

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Keywords          : kbdocfix kbvfp 
Technology        : kbVFPsearch kbAudDeveloper kbVFP300 kbVFP300b
Version           : WINDOWS:3.0,3.0b

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