I myself experienced that problem, which meant that I was not able to use for several weeks in VB 5

As a programmer you should know how to clean the registry manually.

The error is most common when you install VB5 the programming software in a computer that has a VB5 program with OCXs already installed.

Search the registry for Comdlg32 or Richtx32, etc. without the extension and delete the whole key that it is in it, keep searching until you couldn't find it no more. That is it, you could use the API to register it, works much better than Regsvr32, if you do use regsvr32.exe then use it from MS-DOS prompt rather than from the Start\Run.

With Comctl32.ocx is a bit different, you need to restart computer after deleting all traces of it in the registry.

[Note: Regclean is supposed to handle things like this. I'm not sure I trust it completely, however. A previous version did a little damage to my registry once. Hopefully the latest version is safer, but you should probably back up your registry before you begin in any case. -- Rod]

    Y = (X + 3) * 2

    MySub (X)

For an example, run the following code.

    Private Sub Command1_Click()

    Dim X As Integer



        X = 10

        MsgBox X

        ChangeValue (X)    ' Note the parentheses!

        MsgBox X           ' X is still 10.

        ChangeValue X

        MsgBox X           ' X is now 20.

    End Sub



    ' Double the value of the parameter.

    Private Sub ChangeValue(i As Integer)

        i = i * 2

    End Sub

The color palatte is a table listing the (probably 256) colors displayed on your system. The background color is stored in some "random" position, say 69 = &H45. The foreground color is in some other table entry, say 42 = &H2A. You XOR these and get &H42 XOR &H2A = &H68 = 104 (if I didn't mess up the math). That means you get whatever color happens to be in table position 104. Today it could be dark red. Tomorrow it could be something else.

The easiest thing to do about all this is nothing. Use vbInvert instead of XOR and don't worry about the colors you get.

The system palette includes 20 static colors that have fixed values. They live in the first 10 and last 10 palette entries. They are arranged so the inverse of one gives another that contrasts well. That means if you use those colors and you draw using vbInvert, the result usually contrasts well so you can see it.

If you really want to get exactly the color you want, you are probably better saving a copy of the image so you can erase by restoring it. Then draw copy pen mode using red or whatever. Annoying, I know.

    Dim frm As New MyForm



        MyForm.Caption = "This is the single instance"

        frm.Show

Start the VDM from the Visual Basic 5 Add-Ins menu. To create a new Access database, File\New\Microsoft Access\Version 7.0 MDB. Then enter the name of the new .mdb file to create.

To create a new table, right click on the Database window and select New Table.

To add fields to the table, click on the Add Field button. In the dialog that pops up, enter the field information: field name, data type, size (for text), AllowZeroLength, Required, etc. When you are done with that field, click Ok. The dialog stays up so you can create more fields. Click Close when you are done adding fields to the table.

When you have closed the fields dialog, you can create indexes for the table. Click on the Add Index button. Click on the fields you want to make up the index. Be sure you select them in order. Give the index a name and click the Ok button.

When you have finished describing the table, click the Build the Table button to actually create the table. You will see it appear in the Database window. Expand the TreeView representation of the table to see the list of fields. Expand a field name to see the field's properties.

To change the table's design (add or remove fields, change field definitions, etc.), right click on the table's name and select Design. To add, remove, and edit records in the table, right click on the table's name and select Open.

This should be enough to get you started. The VDM is cumbersome but useful. Most of the features are hidden inside context menus that you must right click to find. Right click on different objects to see what else you can do.

These examples are normal software for money, with a demo version. If you sell software like this, be honest and do not call it shareware or freeware. Call the restricted version a demo version.

There are several ways you can limit a program to produce a demo version. There are some products you can buy that make this easier. I won't talk about them here, though. You can search the Web for them if you like.

The easiest way to provide a limited demo version is to make it functionally restricted. For example, make it load its data using an internal subroutine instead of loading from a file. Or disable the save features. Because the demo version and the full license version are different executables, there is no possibility of someone with a demo version making it run in full-license mode.

A traditional method is to provide a guilt screen. Every 10 or 30 minutes, the program presents a dialog saying, "You really should send in $10" or whatever. If they do, you tell them how to deactivate this screen. This is very annoying, but at least you are being fairly true to the idea of shareware. The user does not have to pay if he is willing to live with the guilt screen.

Finally, you can provide some sort of time limit or restricted protection. Realize that it is hard to protect your software completely. For example, if you time limit the software, the user can always reset his system clock if he really cares. It is easiest to just provide a separate restricted demo version.

To implement restricted features, provide a password that includes the information you need the program to have. For example, if the software has an expiration date, include it in the password. Also include some other junk to make the password more complicated and make the program verify that the password is legal.

Now encrypt the password using your favorite technique. For a serious study of cryptography, see the book Applied Cryptography.

For example, you might make the plain text version of the password be watcher01ext20end99. This will encrypt to something apparently meaningless like 1fDjh9U34jfh8Kh8747. This is the value you give to the user. During installation, you can save it to the registry if you like so the user does not need to type it in all the time.

When the program loads, it reads this password either from the user or from the registry. It decrypts it to get the original value. It verifies that the string has the format watcher--ext--end--, and it extracts the expiration date 01/20/99. It then verifies that the date has not arrived.

You can use a similar technique to store codes that indicate which functions should be allowed. Then you can make the same program work in demo or full-feature mode using different passwords.

What you need to do is leave the error handler and resume normal execution. Then you can use On Error to establish a new error handler for the next error. You do this with the Resume statement. See the help for details. In this case, you can use Resume LineLabel to make the program continue execution at a specific line.

Unfortunately, executing Resume from outside an error handler generates an error. Thus you cannot place the error handler in the flow of code the way you have. You need to jump out to the error handler and jump back with Resume.

Below is a subroutine that demonstrates two error handler.

    Private Sub Command1_Click()

    Dim i As Integer



        On Error GoTo Error1

        i = 1 / 0   ' Divide by zero.

    Error1Resume:

        On Error GoTo Error2

        i = 1000000 ' Too big--overflow.

    Error2Resume:

        MsgBox "Finishing."

        ' Do not fall through into the error handlers!

        Exit Sub



    Error1:

        ' Resume ends error handler mode.

        MsgBox "First error handler."

        Resume Error1Resume

    Error2:

        ' Resume ends error handler mode.

        MsgBox "Second error handler."

        Resume Error2Resume

    End Sub

    Do While col.Count > 0

        col.Remove col.Count

    Loop

    Do While col.Count > 0

        col.Remove 1

    Loop

    Dim col As Collection



        ' Allocate the collection and use it.

        Set col = New Collection

            :

        ' Destroy the collection.

        Set col = Nothing

    Private hidden_data As Integer



    Public Function GetData() As Integer

        GetData = hidden_data * 2

    End Function

On the other hand, if you have a routine that applies to a more general group of "thing" than these objects, or if it does not naturally belong to any kind of object, the routine should be in a standard module.

For instance, you might have a routine that averages the numbers in an array. Your program might use lots of different kinds of arrays. You could create a class that wrapped up the functionality of an array and give it an Average method, but that would probably be over elaborate.

Personally, I use a class when either:

1. I need to create a bunch of similar objects
2. I want to use class methods and properties to increase encapsulation and hide functionality

1. Save the edit version with SaveFile (because we're going to modifiy the heck out of it).
2. Convert the edit version to a print version:
   1. Run through the entire document changing SelIndent and SelRightIndent to values appropriate for the printer (indent values in the edit version are appropriate for the screen, not the printer).
   2. Make any other changes; in my case, add page headers and eliminate scene numbers.
3. Print one page at a time with a SelPrint loop. Counting lines is tricky. Finding LFCRs is easy but I had to also account for line wraps which bump the line count, and page overflows which must not be allowed to happen.
4. Delete the print version with SelRTF="".
5. Reinstart the edit version with LoadFile.

    Printer.PaintPicture MSFlexGrid_Name.Picture, 0, 0

    Printer.EndDoc

    Dim old_width as Integer

    MSFlexGrid_Name.width=printer.width

     MSFlexGrid_Name.width=old_width

    For i = 1 To num_copies

        ' Print the document here...



        Printer.NewPage

    Next i

    Printer.EndDoc

    Printer.ScaleLeft = -0.5 * 1440

    Printer.ScaleTop = -0.75 * 1440

    Printer.CurrentX = 0

    Printer.CurrentY = 0

For preview, pass the routine a hidden PictureBox. Then use PaintPicture to copy the hidden picture to a visible PictureBox at the desired scale. Drawing at full scale on the hidden PictureBox first allows you to scale fonts and other graphics without distortion.

System Issues

Check Resources
(By Theodore Fattaleh)
When making a program, its important to check and see how much resources it is using. Use the Resource meter and check it by running the .exe, don't check it from Visual Basic because it will not show resources usage.

To make your program use less resources:

• Use label1 instead of Textboxes if you can.
• Use less graphic.

Small programs and always running programs, should use 1% to 3%. Average program in VB should use between 4% and 5% resources. Advanced large programs, 6% to 8%.

If your advanced large program uses more than 8% then there is something wrong. Compare your program to Microsoft Word or Internet Explorer. See if multiple instances do a major drain on resources.

Run all tasks in your program and see if resource usage has increased.

Check resources before opening your program, then check resources after you closed your program. Be sure that your program resources usage has been restored and didn't do a permanent resources drainage that would require a reboot to restore.

Use the

    Set Form1 = Nothing

He also found some code somewhere on the net that installs a font in a more "official" way (If you recognize it, tell me where it came from originally so I can give credit to the author). To download it exactly as he got it from the net, click here.

Use this technique to start your favorite programs when you press some hotkey combination. For example, when you type Ctl-Alt-W, you can start Word.

1. Right click on the Start menu. Select the Explore command to explore the Start menu directories.
2. If the program is not already in your Start menu or one of its submenus, add it there. You might want to create a new Hotkeys folder so you know where all your hotkeys are defined.
3. Locate the program in the explore window. Right click on it and select Properties.
4. Click on the Shortcut tab. Click on the Shortcut Key field and press the letter you want associated with the program. For example, if you press N, the shortcut key combination will be Ctl-Alt-N.
5. Click the OK button. You can also close the Explorer window started in step 1 if you like.

The new project comes with a class that will become the DLL's server object. Give it a reasonable name. Also give it public methods that will be available to the client application.

That's all you really need to do, but there is more that can make your ActiveX DLL easier to use. In the Project menu, select the Project1 Properties command at the bottom. In the General tab, give the project a meaningful name and description. On the Make tab, you can also enter the company name, copyright information, etc.

Click Ok and you are ready to build the DLL. In the File menu, select the Make Project_Name.dll command. That's all there is to it.

To use the DLL, create a new Standard EXE project. Select the Project menu's References command. In the dialog, find the new DLL. It will be listed using the description for the project that you entered in the project properties General tab.

Now the program can declare variables of the server class type. If your server class is named MyClass, then the program can say:

    Dim obj As MyClass



        Set obj = New MyClass

        obj.PublicProcedure

The easiest way to ensure that the DLLs are present is to use a setup kit. Run the Setup Kit Wizard (VB5 and earlier) or the Packaging and Deployment Wizard (VB6). It will build a setup kit for the program.

When the Wizard gives you a chance to add and remove files, do not remove any files. While you may not use OLE yourself, the program needs an OLE DLL to run. The Wizard usually knows what is necessary.

Then execute the setup kit on the other computer. It will install the program and the necessary DLLs so you can run it on the other computer.

    Option Explicit



    #If Win32 Then

        Private Declare Function ShutdownWindows Lib "user32" Alias _

            "ExitWindowsEx" (ByVal uFlags As Long, _

            ByVal dwReserved As Long) As Long

    #Else

        Private Declare Function ShutdownWindows Lib "user" Alias _

            "ExitWindows" (ByVal wReturnCode As Integer, _

            ByVal dwReserved As Integer) As Integer

    #End If

    Private Const EWX_LOGOFF = 0

    Private Const EWX_SHUTDOWN = 1

    Private Const EWX_REBOOT = 2

    Private Const EWX_FORCE = 4



    Private Sub Command1_Click()

        ShutdownWindows EWX_FORCE, 0

    End Sub

    r = color And &HFF&

    g = (color And &HFF00&) \ &H100&

    b = (color And &HFF0000) \ &H10000

Public Declare Function GetSysColor _

    Lib "user32" Alias "GetSysColor" _

    (ByVal nIndex As Long) As Long

        :

    If color And &H80000000 Then _

        color = GetSysColor(color And &HFFFFFF)

One final case occurs if you use Point to get the color of a pixel that does not exist. For example, on a form with ScaleMode = vbPixels, Point(-100, -100) returns -1 because there is no pixel at (-100, -100).

The following subroutine breaks a color into its components. If the color is -1, the routine leaves r, g, and b unchanged. Depending on your application, you may want to set them to default values such as 0 or 255.

Public Declare Function GetSysColor _ Lib "user32" Alias "GetSysColor" _ (ByVal nIndex As Long) As Long ' Break a color into its components. Private Sub BreakColor(ByVal color As Long, _ ByRef r As Long, ByRef g As Long, _ ByRef b As Long) If color = &HFFFFFFFF Then Exit Sub If color And &H80000000 Then _ color = GetSysColor(color And &HFFFFFF) r = color And &HFF& g = (color And &HFF00&) \ &H100& b = (color And &HFF0000) \ &H10000 End Sub

Thanks to Horst F. Haupt (HorstFH@aol.com) and Kenneth Biel (Kenneth.Biel@wcom.com) for their suggestions.

For example, if you load compressed JPEG images into a form at design time and then create a compiled executable (in VB5), the executable will be smaller than it would had you used BMP images. This lets you cram a lot of pictures into a reasonably small image.

If you use PaintPicture to copy an image, the new picture is always in the larger, faster BMP format. If you need to speed the program up, save pictures in JPEG format. Then at run time use PaintPicture to copy them into new controls so you can display them from the BMP format.

Coding Techniques

Learn Object Types
(By Rod Stephens)
If you want to know whether it is a particular type, do something like:

    If TypeOf obj Is ListItem Then ...

If you want the name of the object's type, use:

    MsgBox "The item is a " & TypeName(obj)

When you have trapped inside a non-ending loop, as you cannot press any command buton or key, the only sulution is placing the command "DoEvents" at the first line inside the loop:

Dim i As Long



    For i = 1 To 1000000

        DoEvents

        ...

    Next i

Well, I have found that generally it's better to use the API function GetInputState to check the presence of events in the app's input queue. I don't know why the addiction of an "If" statement improves the code speed, but it works very fine.

So you could replace the row

    DoEvents

    If GetInputState() Then DoEvents

[The reason this makes things faster is that DoEvents allows all applications to process events, not just yours. This test allows DoEvents to run only when your program has events. -- Rod]

Let us say that you are creating a string, by letting the user click on various combinations of labels...

    lbl(0) = "Hello "

    lbl(1) = " I'm "

    lbl(2) = " Happy"

    lbl(3) = " Sad"

    ...



    sub lbl_click (index as integer)

        string$ = string$+lbl(index).caption

    select case string$

        case "Hello I'm Happy"

            do something

        case "Hello I'm"

            this would be an error...

        case else

            do something else

    end select

So I created an array as large as the number of labels:

    arraylbl(n) as integer

    lbl(0) and lbl(1) = 1 + 2 = 3

    lbl(0) and lbl(1) and lbl(4) = 1 + 2 + 16 = 19

You can easily set up a select case, based upon just a few valid numbers:

    select case IsLegal

        case 3

            ' the string was valid

            call goodstuff

        case 19

            'the string was valid

            call goodstuff

        case  else

            'invalid

            call nogood

    end select

1. Open the Excel Database.
2. Save it using File/Save_As/DIF_(data Interchange Format) Give it any name except the original name.
3. Open Access
4. Start a new data base (any rubbish at all - not relevant to solution but just need something open.
5. Goto Menu/File/Get_external_data/import
6. Follow usual procedure for opening a file except to set it as Excel and find your excel file
7. Click Import.
8. Click Next
9. Click First_row_contains_fieldnames (if true)
10. Click ok to change/adapt to suitable names
11. Click Next
12. Click new table (?? I think I had a problem using existing table - the existing one can be dumped later ??)
13. Click next
14. Read instructions and make any changes you think fit - I made none!

First, start a new project. Get it loaded the way you want. Add controls to the toolbox, give it multiple forms and modules, add controls to the forms, place code in the forms and modules, etc. Do whatever you like that you can do in a normal project.

Next, save it all in your the Projects directory. I'm not sure where this directory is for all systems. On mine (WindowsNT/VB6), it's:

    C:\Program Files\Microsoft Visual Studio\Vb98\Template\Projects

This goes strongly against one of the fundamental principles of Windows: that the user should always be in control. It takes control away from the user. It would also allow naughty people to create password grabbers and lock a computer against the user's wishes.

In Windows 95 you can disable Ctrl-Alt-Del and Alt-Tab using the SystemParametersInfo API function. This does not work in Windows NT (I don't know about Windows 98). For the reasons above, I suspect it will be hard or impossible to do this in Windoes NT. This is unfortunate because I know there are some legitimate reasons why a computer might want to do this. For example, in some other operating systems, you can specify a program for the computer to run when it boots. Unless you have system privileges, you cannot stop the program or switch to another.

Jarmo Lepola wrote an interesting program that locks the computer until the user enters a password ("mouse" in the example program). In Windows NT, the program grabs the focus many times per second so the user cannot do anything useful until entering the password. [Download it]

A few other people also suggested using SystemParametersInfo including:
Bryan
Marc Strother
James Wilson

Thanks for the suggestions!

The idea is you create a topic file containing the text of the help. You use an arcane set of footnotes defined by Microsoft to indicate links, topic titles, index entries, etc. You save this file in RTF (Rich Text Format), a format supported by many advanced editors including Word.

Next you create a project file that defines some topic numbers and identifies the help source file(s). You run the help compiler to produce the finished .HLP file.

Finally, your program can use the CommonDialog control's ShowHelp method to display the help file. To see an example program that does this, go to http://www.vb-helper.com/HowToBeg.htm and click the "Implement standard File and Help menu commands" link.

All in all, creating help is quite difficult. The help compiler itself is unfriendly and slow, particularly for large help files. If you have an error, the compiler is uninformative. The Help Compiler Workshop puts a front end on some of the process, but it's still hard. Some third party help systems make things easier.

My book Advanced Visual Basic Techniques contains some information on building a help file. I do not know of a book that covers only help, though there are a few introductory books that cover help to some degree.

You might also consider HTML help. Microsoft is pushing it as the method of the future. That does not mean traditional help will go away any time soon, however. I don't know how to create Microsoft's fancy compressed help files (they probably have a tool), but you can easily create your own HTML pages with hyperlinks to provide a quick and easy help system. Advanced Visual Basic Techniques also discusses this method.

• Null. Null is a Variant subtype like Integer or String. It represents a variant that contains no valid data. This is different from zero, Nothing, Empty, or vbNullString. Most other values when combined with Null produce a Null result. For example:

      Null - Null      is Null not 0
  
      Null + 7         is Null not 7
  
      Null = Null      is Null not True
  
  

  You can use IsNull to determine whether an expression is Null:

      If IsNull(my_variable) Then ...

• Empty. This is a variant subtype like Integer or String. It represents a variable that has not yet been initialized. This is different from Null which represents a value that specifically contains no valid data.

  A variant variable that has not yet been initialized has the value Empty. You can use IsEmpty to see if a variant has been initialized.

      If IsEmpty(my_variant) Then ...

• Nothing. This is an object reference that points to no object. Set an object reference to Nothing to free that reference. If no other references point to the object, Visual Basic will destroy the object.

      Dim obj As Form1
  
              :
  
          Set obj = Nothing ' Free the object reference.
  
  

  Use Is Nothing to determine whether a reference points to nothing:

      If obj Is Nothing Then ...

• vbNullString. This constant represents an empty string. This is not the same as a blank string "". It is a nothing string. It is treated as an empty string "" for most Visual Basic purposes. Its real use is for passing null parameters to library functions.

    Dim txt As String

    Dim blank As String



        blank = ""

            : 

        If Len(txt) = 0 Then ...

        If txt = vbNullString Then ...

        If txt = "" Then ... 

        If txt = blank Then ...

    Function LastInStr(txt As String, pattern As String)

    Dim pos1 As Integer

    Dim pos2 As Integer



        pos2 = 0

        Do

            pos1 = pos2

            pos2 = InStr(pos1 + 1, txt, pattern)

        Loop While pos2 > 0

        LastInStr = pos1

    End Function