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

Last reviewed: January 30, 1997
Article ID: Q136070

The information in this article applies to:

Microsoft Visual FoxPro for Windows, versions 3.0, 3.0b

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:

   ARTICLE-ID: Q106161
   TITLE     : How to Convert Screen Object Positions Between Platforms

   ARTICLE-ID: Q129208
   TITLE     : Pixel Replaces Foxel as Default Scale Value in Design Mode

KBCategory: kbprg kbdocerr kbdocfix
KBSubcategory: FxotherDochelp VFoxWin buglist3.00 5.00
buglist3.00b
Additional reference words: docerr 3.00 3.00b navigation buttons

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Last reviewed: January 30, 1997
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