Visual Basic 6.0 Notes

PushKeys

The PushKeys command is available for VB 5.0 and above only. This is the only reason I moved from VB 3.0 to VB 6.0. PushKeys works more than 100 times faster than the VB SendKeys commnad. However, the keystrokes appear to be queued until a DoEvents command is executed. Normally, this would not be a problem except that DoEvents stops the execution of the VB 6.0 application.

  formSave = Screen.ActiveForm.Caption
  AppActivate DOSAppName$     ' Transfers control to the DOS application
  PushKeys DOS_ScreenCapture$ ' Send keys to the active (DOS) application
  
    ' The following 4 lines of code are not needed in VB 3.0,
    ' These are needed so that the clipboard will be available
  For i = 1 To 10       ' I tried various values - 1, 10, 1000 - 
                        ' 1 failed, 10 works sometimes, 1000 hung
   DoEvents             ' Without this - Error - Can't Open Clipboard
  Next i
  AppActivate formSave  ' Without this, DoEvents hangs the application

    ' The following code never fails in VB 3.0, is intermittent in VB 6.0
  tt$ = Clipboard.GetText()

According to Microsoft, DoEvents returns control to the Visual Basic program after the operating system has finished processing the events in its queue and all keys in the SendKeys queue have been sent. The Sleep 32-bit API function is a subset of the DoEvents function.

I tried to develop a template in one directory and do a save as in another directory. I ended up modifying the wrong data and lost the template. There is no way to modify the directory where project members are saved except to delete and reload them. I have not yet figured out how to determine where exe's are created.

File Commands

There is no documented way to test for the existance of a file. Use Name "filename1" as "filename2" to rename a file.

Use the dir command.

Project Definition

How is a project defined? The top level file appears to be an ASCII *.vbg (Visual Basic Group Project) file which points to an ASCII *.vbp (Visual Basic Project) file. A project can contain several frm (form) and bas (Basic module) files. The filenames and paths are stored in the vbp file. This is the only place that these can be seen or edited.

Line Continuation

In order to continue a command on the next line, terminate the line with a space, underscore, enter.

Both of these should give the same result

   Dim Msg   ' Declare variable
   Msg = "1st part of string "
   Msg = Msg & "Next part of string "
   Msg = Msg & "Last part of string"

   Msg = "1st part of string " _
         & "Next part of string " _
         & "Last part of string"

Available starting with VB 4.0

Use the Object Browser to determine the methods and properties of objects.

VB has 34 base classes. Of these, 20 are UI controls, 7 are defined in Global (App, Clipboard, Forms, Licenses, Printer, Printers, Screen). The others are Form, MDIForm, Menu, PropertyPage, UserControl, UserDocument, VBControlExtender.

Setting Variables on a Form

Property functions let you create custom properties for forms and class modules. Properties are accessed using the PropertySet, PropertyGet, and PropertLet statements. First, declare the property as a form-level variable

   Private TempStr as String

Then add the following procedures to the form

   Public Property Let FormVariable(str as string)
       TempStr = str
   End Property
   Public Property Get FormVariable()
       FormVariable = TempStr
   End Property

The property is now set using

   Form1.FormVariable = "test"

Event Calling Sequence

For a Form

  Initialize --> Load --> Form_Activate

Screen.ActiveControl is not valid during either Initialize or Load, but is valid during Form_Activate

Form_GotFocus appears to never get called.

Clicking a control generates 3 events in a control specific order.

Control	Event Order
ListBox CommandButton	MouseDown --> Click --> MouseUp
FileListBox Label PictureBox	MouseDown --> MouseUp --> Click
Form TextBox	Unknown

Missing Features

These are some of the more common features missing from Visual Basic 6.0

The PictureBox control is the primary control to contain other controls. It can be Sunken 3D or Flat only.
The Frame can also contain buttons, but is Flat or Chiseled only.
There is no way to align any control to the client except to write code.
The tutorials are hard to find. (Search help for 'tutorial')
There are many missing controls - Status bar, Progress Indicator
Buttons are operated with the space bar, not the Enter key.
The user interface menus scroll vertically - uck!

Debug

You place break point by clicking in the Left-hand gray border. If a red dot appears, the program will pause and be displayed in the debug window when that line of code is executed.

In debug mode, double click a variable to see its value. Sometimes, simply pointing to a variable will display its value, but double clicking works on more variables.

In order to single step the program, you must first display the Debug Toolbar. This is hidden in View / Toolbars / Debug which is not visible on a 640x480 display unless you scroll the View menu to display the Toolbars selection. (In my opinion, this rates significantly below poor design. Scrolling a menu is never acceptable!)

File Types

*.frm	Form Description
*.frx	Form Extension file Various strings, default data, etc. Not text files
*.bas	Library files
*.cls	Code to create new objects
	ActiveX Documents (pro)
	ActiveX Designers (pro)
	User Controls (pro)
*.vbw	Windows Locations
*.vbg	VB Group - Identifies the startup project
*.vbp	Project files - Lists the included files, the name and path for the exe, who the software is licensed to

xx

When converting from VB 3.0 to VB 6.0, the common dialog controls changed.

You must manually add ComDlg32.OCX ActiveX control to each application. In VB 3.0, CommDlg.dll was accessed via cmdialog.vbx Because the VB 6.0 help says to use CommDlg.dll, the detailed instructions do not work.
The constants changed. Setting
```
   CMDialog.Flags = OFN_FILEMUSTEXIST + OFN_HIDEREADONLY
```
no longer hides the readonly checkbox. You must use cdlOFNFileMustExist and cdlOFNHideReadOnly instead.
Basically, all constants must be replaced with their new values.

Things wrong with the FileOpen... dialog box.

You can't resize the box to make it readable
You can't force it to open in details mode
It can't show the directory tree in a separate panel
It can't show the complete path
You can't change the column order
No search direction / search column indicators
Can't add additional columns (attributes, date created, extension)

Humm, it seems that it is better to write your own and to blow off the weak standard dialog box. However, the properties and methods should still be as similar as possible. Perhaps both sets of constants (3.0 and 6.0) should be supported in order to simplify code migration.

xx

Visual Basic is dangerous. Several times now, I have generated small projects to test something, then copied the code to another directory to include it in a larger project. Suprise ... all the changes were made to the original code which I was trying to preserve ... not the copy.

The problem appears to be that the *.vbp (VB project) files contain hard coded paths, such as

Module=GlobalConstants; ..\..\..\Program Files\Microsoft Visual Studio\VB98\GlobalConstants.bas
Module=Module2; ..\TestDosApp\globcons.bas

must inspect this file yourself before doing any work.

It is a real pain that the project name can't be the same as the form name even though they have different extensions. Real languages provide more freedom.

Referencing a Form

The main help for the following is under Data Types. Object variables, such as CallingForm below, are allocated 4 bytes for a 32-bit address which points to the actual object. Variables are associated with objects by using the set command. The help suggests using specific classes rather than a generic parent (e.g. Form instead of Control) so that the compiler can perform error checking.

dim CallingForm as Form

sub subName(formVar as Form)
  CallingForm = formVar      ' This fails
  set CallingForm = formVar  ' This works
end sub

  CallingForm.UIText.text = "string"  ' This works

In the main form, use this to pass the form reference

  call subName(me)

Fonts

When working with Courier New and a Picture Box, the fonts are irrational. If you set the fontSize = 8 it is actually set to 8.25!

xx

References

www.softcircuits.com
www.planet-source-code.com/vb
Many hints are available from comp.lang.basic.visual.misc

xx

I am trying to generate generic code which implements cut, copy, paste, and delete on text objects.

   Screen.ActiveControl.SelText

can access the selected text, but how do I know if the ActiveControl is a text box and not a button? Well Screen.ActiveControl returns a control. However, there is no built-in help for control - no members, no properties, no parent, nothing. Neither the help file nor the fabulous Object Browser provides any information.

The help for ActiveControl contains a partial answer: TypeOf returns the object's type. However, the help for the TypeOf keyword points to If..Then..Else and provides no additional help at all. (The help for VB 3.0 and VB 6.0 are equally bad.) Searching the Object Browser for TypeOf returns No items found.

   ActiveForm.ActiveControl

does not work, it has no value even though it is the example used for the ActiveForm help example. Therefore, the rule is Don't trust the help files!

Additional TypeOf help is provided under Clipboard / checking data formats .

****************

It would make a lot more sense if the UI Controls had built-in overloaded virtual functions which handled these basic commands.

The whole point of object oriented programming is that you can treat an unknown object as a base object in the class hierarchy and execute overloaded methods without knowing, or caring, what the specific type of the object is.

VB 6.0 fails totally as an object oriented language.

Converting 3.0 to 6.0

Converting VB 3.0 to 6.0 is a real pain.

The built-in constants are re-named.
Functions work different.

For more info see VB_3_0_To_6_0.htm

Author: Robert Clemenzi - clemenzi@cpcug.org