In this chapter let us create an ActiveX EXE,
which is also called as out-of-process
server. One of the major advantages of the out-of-process server is, it can be
run on a different machine from client machine and thus enabling you to develop
Application Server in 3-tier
client/server architecture. ActiveX Exe could also be run as a separate
program. It is suitable for cases where you need to create an application that
may be invoked as a standalone application or as a server. When it is invoked
as a standalone application then users can interact with the application.
To get a feel
of out-of-process server and how to use it in client application, let us create
an out-of-process server that uses the Time
class (created in the previous chapter), and testing application.
The
ActiveX EXE that we are about to create contains the following features.
¨
It has a single class Time (taken as it is from previous
chapter).
¨
A form that is displayed only
when ActiveX EXE is invoked as a standalone application. The form is hidden
when ActiveX EXE is invoked from a client application (used as a server).
¨
The form of ActiveX EXE is used
to display running digital clock using Time
class of the ActiveX EXE
¨
Client application as usual
uses an object of Time class to invoke methods such as GetTime, SetTime etc.
¨
The startup object of ActiveX
EXE is Sub Main, which is a
procedure in code module. Main procedure determines whether form in server is
to be displayed or not depending upon whether server is invoked as standalone
application or invoked by client application.
Creating an ActiveX EXE
Let us start creating ActiveX EXE and its
components like code module and form.
1.
Create a new project using File -> New Project and select ActiveX
EXE as project type.
2.
Visual Basic creates a project
with just one class module named Class1.
3.
Invoke Project Properties and
click on right button.
4.
Select Add -> Class Module from popup menu.
5.
In Add Class Module dialog
select Existing tab and select TIME.CLS.
6.
Click right button on Class1
and select Remove Class1 from popup
menu. When you are prompted to save it, select No.
7.
At this stage, we have only one
class module (TIME) in our project.
8.
Add a form using Project -> Add Form and select a
simple form from Add Form dialog box.
9.
Add a code module using Project -> Add Module and click on Open in Add Module dialog box.
10.
At this stage, the project
explorer
11. Change the following properties of the project.
Project name AEXETIMESERVER
Project Description Time
class in Out-of-process server by P.Srikanth.
Startup object Sub Main
12. Create a procedure with the name Main in code module and write the following code.
Public
Sub Main()
If
App.StartMode = vbSModeStandalone Then
frmTime.Show
End
If
End Sub
Listing
26.1: Code for Main procedure of code module.
App object is one of the system objects. If StartMode
property contains vbSmodeStandalone, it means ActiveX EXE is run as standalone
program. The other option is vbSmodeAutomation.
13.
Invoke Form designer and place
a label and a timer control on the form.
14.
Change the following properties
of the form and controls.
|
Object
|
Property
|
Value
|
|
Form
|
Name
|
FrmTime
|
|
|
Caption
|
ActiveX EXE Server
|
|
Label1
|
Name
|
Lbltime
|
|
|
Caption
|
00:00:00
|
|
|
Autosize
|
True
|
|
|
Fontsize
|
14
|
|
|
Borderstyle
|
1-Fixed
Single
|
|
Timer1
|
Interval
|
1000
|
15. Write the following code for frmTime form.
General/Declarations
Dim t As New Time
Private
Sub Form_Load()
Timer1_Timer
End Sub
Private
Sub Timer1_Timer()
t.SetToCurrent
lblTime.Caption = t.GetTime
End Sub
Listing
26.2: Code in Form.
16. Save the project and its component under the following names (if you
want you may give different names).
Project aexetimerserver.vbp
Form frmtime.frm
Module aexemodule.bas
Class Module aexetime.cls
Time class is taken from previous project. If we make any changes to
time class and save them, the changes will be saved under Time.cls and this might effect the previous project (timerserer).
So it is better we have a separate copy of Time class for the AEXETIMERSERER
project.
To
save time.cls under a different name:
1.
Select Time class in project explorer and click on right mouse button.
2.
Select Save
Time.Cls As option from popup menu and enter AEXETIME as the name of the
new file.
3.
Time class is now stored under
a new name - AEXETIME.CLS. It doesn’t
effect TIME.CLS and previous project
continues to use TIME.CLS.
Creating
.EXE file
1.
Select File menu and choose Make
aexetimeserver.exe option.
2.
Visual Basic creates aexetimeserver.exe in the specified
directory and also registers it in system registry.
Running ActiveX Server as Standalone
application
Let us run aexetimerserver.exe as a standalone application. In this case it
should display frmTime, which contains
running digital clock.
To
run ActiveX exe server as standalone application:
1.
Click on Start button on Taskbar
2.
Select Run option from the start menu
3.
Click on Browse button in Run window and select aexetimerserver.exe
4.
After selecting the file click
on Ok to run the program.
5.
A small window (frmTime) is
displayed with running digital clock
Running client
application
We use the same
client program that we used for ActiveX DLL.
But client application should have a reference to ActiveX EXE. So open client application (timetest.vbp) and follow the steps
given below.
To create a reference to ActiveX EXE:
1. Select Project
-> References
2.
Uncheck Time
class by P.Srikanth
3.
Check
Time class in Out-of-process server by
P.Srikanth.
4. Click on Ok
Run client
application by pressing F5. You should see the same screen as you have seen in
the previous chapter and it also functions in the same manner. But one
important difference is that now, Time class is in a separate process. And it
could also be running on a separate machine altogether. If it runs on a
different machine then you are accessing an object that is on a different
machine and access to such object is handled by DCOM (distributed Component
Object Model).
Another important
point to be noted here is, when you are
invoking ActiveX EXE from client application, frmTime is not displayed. But the application is loaded and Time class
is provided to client application. Remember, we have checked for the startup
mode and displyed frmTime form only when startup mode is standalone.
That is all you
need to do to create an ActiveX EXE. The basic advantatge with ActiveX EXE is-
it can run as a separate process. That could as well be on a seperate machine.
So think of ActiveX EXE if they are the matters of concern. If you are looking
for a collection of classes and no need to run them separately then implement
the collection of classes as an ActiveX DLL. ActiveX DLL (in-process server) is
much faster than ActiveX EXE (out-of-process server).
Instancing Property of
Classes
The value of the Instancing property determines whether your class is private — that
is, for use only within your component — or available for other applications.
As its name suggests, the Instancing property also determines how
other applications create instances of the class. The property values have the
following meanings.
|
Option
|
Meaning
|
|
Private
|
Means that
other applications aren’t allowed access to type library information about
the class, and cannot create instances of it. Private objects are only for
use within your component.
|
|
PublicNotCreatable
|
Means that
other applications can use objects of this class only if your component
creates the objects first. Other applications cannot use the CreateObject function or the New operator to create objects from
the class.
|
MultiUse |
Allows other
applications to create objects from the class. One instance of your component
can provide any number of objects created in this fashion. An out-of-process
component can supply multiple objects to multiple clients; an in-process
component can supply multiple objects to the client and to any other
components in its process.
|
|
GlobalMultiUse
|
Is like
MultiUse, with one addition: properties and methods of the class can be
invoked as if they were simply global functions. It’s not necessary to
explicitly create an instance of the class first, because one will
automatically be created.
|
|
SingleUse
|
Allows other
applications to create objects from the class, but every object of this class
that a client creates starts a new instance of your component. Not allowed in
ActiveX DLL projects.
|
|
GlobalSingleUse
|
Is like
SingleUse, except that properties and methods of the class can be invoked as
if they were simply global functions. Not allowed in ActiveX DLL projects.
|
Table
26.1: Options of Instancing property.
Class Modules and Project Types
The value of the Instancing property is
restricted in certain project types. Allowed values are shown in the following
table:
|
Instancing Value
|
ActiveX EXE
|
ActiveX DLL
|
|
Private
|
Yes
|
Yes
|
|
PublicNotCreatable
|
Yes
|
Yes
|
|
MultiUse
|
Yes
|
Yes
|
|
GlobalMultiUse
|
Yes
|
Yes
|
|
SingleUse
|
Yes
|
|
|
GlobalSingleUse
|
Yes
|
|
Registration of ActiveX Components
Every ActiveX
component is to be registered in Windows registry. Unless a component is
registered, system has no way to get the required information about these
components.
Visual Basic
creates an entry in the registry for each component as and when component is
compiled. But that is the case only with the system in which component is
created. But as you can guess, you need to develop component only for once and
then install it in other machines. When a component is loaded into another
machine (different from development machine) you cannot access the components
unless components are registered in windows system registry.
When you buy
components, they come with an installation program, which takes care of
installing and registering components in client’s machine.
Buf if you ever
want to register an ActiveX component ,be it DLL or EXE or OCX, you can use REGSVR32
program available in windows\system
folder.
To get help
regarding REGSVR32.EXE, just enter
REGSVR32 at system prompt after getting into WINDOWS\SYSTEM directory.
To
register TIMERSERVER.DLL, enter:
1.
Copy timerserver.dll into required directory. Let us assume the name of
the directory is servers, which is
in root directory of C drive.
2.
Enter into windows\system
directory. because regsvr32.exe
resides in windows\system directory. and normally windows\system directory is
not in the path. Otherwise you can invoke it from anywhere.
3.
Invoke regsvr32 to register timerserver.dll
as follows:
Regsvr32 c:\servers\timeserver.dll
4.
If it is successful, you will
see a window
To
Unregister TimerServer.dll:
If you ever decide to unregister
timeserver.dll from registry, you can use regsvr32.exe
with /u option to unregister the
component.
Enter the following to unregister timeserver.dll.
Regsvr32
/u c:\servers\timeserver.dll
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