This
project shows how an ActiveX Control can be created in VB to
meet a requirement that can't easily be replicated using server-side
scripting or client-side script.
The
scenario involves a requirement to print a certifiable document
in a pre-determined layout from a web site: An achievement certificate
or a licence certificate are typical of documents of this type.
(See the project's flowchart)
VB
is used to create a control which prints the certficate to
the local, default printer. The VB Internet control is
used in the ActiveX to download a certificate number from a
web site which is then included on the page of the printed
document.
To
keep the coding simple I have minimised the error checking
and handling in this ActiveX so it doesn't always fail elegantly
. . . |
|
Start
VB and choose a new ActiveX Control project.
Change
the control's name from UserControl1 to PrintControl
and save the project as CertificatePrint.vbp
Add
a command button to the control, naming it cmdPrint and
set its caption to Print
We'll
place the button and size the control later, so just
leave the control where it is for now. |
 |
|
 |
Next,
add a Microsoft Internet Transfer control to the UserControl
workspace. You may need to right-click the toolbox and
use the Components option to add this control to the
toolbox. (See VB's help if you have any trouble doing
this)
This
control will be used to download the unique certificate
number. This control is invisible at runtime and can't
be sized at design time, so just leave it as it is.
Since
no certificate is complete without a signature, we'll
add a picture box, call it picSignature and set its Picture
property to a suitable graphic (Included in the downloadable
support files, signature.jpg)
The
picture box needs to be sized to match the signature
graphic and its border and background set to match the
white document background. |
| We
now need to write code to print the certificate, so double-click
the command button, cmdPrint to open the code window and
add the code to it's onClick event, as shown below: |
 |
|
Private Sub cmdPrint_Click()
'
' Print a formatted, authenticated certificate to the default printer
'
Const twipFactor = 1440
Printer.ScaleMode = vbTwips
Printer.Orientation = 1
Printer.FontTransparent = True
Printer.FillStyle = vbFSTransparent
Printer.ForeColor = &O0&
'
sWidth = 8.3
sHeight = 12
'
Printer.Width = twipFactor * sWidth
Printer.Height = twipFactor * sHeight
'
Printer.Font = "Arial"
Printer.FontSize = 14
Printer.FontBold = True
Printer.CurrentY = twipFactor * 0.5
Printer.CurrentX = twipFactor * 0.5
Printer.Print Format(Now(), "hh:mm:ss")
'
' Page Header
'
Printer.Font = "Arial"
Printer.FontSize = 36
Printer.FontBold = True
Printer.CurrentY = twipFactor * 1
hWidth = Printer.TextWidth("THIS IS TO CERTIFY") / 2
Printer.CurrentX = Printer.ScaleWidth / 2 - hWidth
Printer.Print "THIS IS TO CERTIFY"
Printer.Font = "Arial"
Printer.FontSize = 18
Printer.FontBold = True
Printer.CurrentY = twipFactor * 1.7
hWidth = Printer.TextWidth("THE AUTHENTICITY OF") / 2
Printer.CurrentX = Printer.ScaleWidth / 2 - hWidth
Printer.Print "THE AUTHENTICITY OF"
Printer.Font = "Arial"
Printer.FontSize = 36
Printer.FontBold = True
Printer.CurrentY = twipFactor * 2.2
hWidth = Printer.TextWidth("THIS CERTICATE") / 2
Printer.CurrentX = Printer.ScaleWidth / 2 - hWidth
Printer.Print "THIS CERTICATE"
'
' Signature
'
Printer.CurrentX = twipFactor * 3.5
Printer.CurrentY = twipFactor * 7
Printer.Font = "Arial"
Printer.FontSize = 14
Printer.FontBold = True
Printer.ForeColor = &O0&
Printer.Print "Signed this " & Day(Now()) & " day of " & _
MonthName(Month(Now())) & _
" " & Year(Now())
sX1 = twipFactor * 4.5
sY1 = twipFactor * 8
Printer.PaintPicture picSignature, sX1, sY1
Printer.CurrentX = twipFactor * 4.5
Printer.CurrentY = twipFactor * 9
Printer.Font = "Arial"
Printer.FontSize = 14
Printer.FontBold = True
Printer.Print "Mortimer Mouse"
Printer.EndDoc
'
Exit Sub
End Sub |
| At
this stage you can test the control by clicking on the
Start icon (the little blue arrow) and, when the test page
has loaded, clicking on the print button (or whatever you
can see of the print button that isn't obscured by the
picture box!) |
So
long as the print seems to be working (looking something
like this)
we can move on to getting the certificate number using
the Internet Transfer Control. Note that the current time
is included on the output, top left. This is just to ensure
that, during any debugging, you can tell which copy is
which. |
|
| Getting
the certificate number |
|
|
Because we have the entire contents of the VB toolbox
at our disposal, getting a file from a remote server is as easy
as it was placing the Microsoft Internet Transfer Control on our
ActiveX Control. What we will do with this control is first ask
the user for a security code which is also the name of a file on
the web server: We will use an Input Box to get the filename.
Next, we'll use the Internet Transfer Control to get the file
containing a certificate number from a URL hardcoded into the
ActiveX, so the user need never know what the URL is or how the
update works. Checking validity consists two steps:
The secure code entered by the user must match the name of a
file on the server (If it's a Unix server, that will be case-sensitive,
too)
The returned certificate number is validated by the ActiveX
control (In this case we simply check if it's six characters
long)
This
is the code: |
Dim
v as Variant
'
Inet1.AccessType
= icUseDefault
v = Inet1.OpenURL _
("www.chrispearson.org/pages/programming/vb/activex/certprint/" & _
InputBox("Please enter your security code", , "hoot") & _
".dat")
'
If Len(v) <> 6 Then
v = "INVALID!"
End If
'
MsgBox ">>>" & v & "<<<"
|
|
Notice that we have included the InputBox in the
parameters of OpenURL. We replace the contents of variable v with
the text INVALID! if the returned certificate number fails our
validity check.
At
this stage we also use a MessageBox to
stop the program and show us the result - Use this a couple
of times to ensure you
are making a connection and returning an expected result. Once
the transfer is working properly don't forget to remove the
MsgBox ">>>" & v & "<<<" code.
We
need to ensure that the certificate is only signed if it is
valid, so change the original code, adding a condition around
the line that prints the signature: |
sX1 = twipFactor * 4.5
sY1 = twipFactor * 8
If v <> "INVALID!!" Then
Printer.PaintPicture picSignature, sX1, sY1
End If
|
|
| And a certificate number needs to be added just before the existing
Printer.EndDoc: |
|
Printer.CurrentX = twipFactor * 4.5
Printer.CurrentY = twipFactor * 10
Printer.Font = "Arial"
Printer.FontSize = 14
Printer.FontBold = True
Printer.Print "Certificate number " & v
Printer.EndDoc
|
|
| Also,
remove the time stamp from the top left corner of the form and
tiday up the control, shrinking it around the command button. |
 |
Move
the command button to the top left . . . |
|
| Then
shrink the control around the button - The other controls
will now not be visible but they're still there! |
 |
|
The
project files, along with three certificate numbers in .dat
files, are available to download in certprint_files.zip. This
archive contains all the VB project files and a compiled .ocx.
And,
finally, it might not be the most sparkling bit of software
in the universe but it does show how you can use ActiveX
to do something you can't do in JavaScript and which
does (at a push) have a real-world application.
Bear
in mind that this project contains nothing in the way
of error handling: If anything untoward happens the ActiveX
dies without grace! The next steps would be a few judicious
OnError GoTos and maybe a Select Case to handle INet1's
return codes. Why
not give it a go? Use the secure code: hippo or
the default value, hoot |
