ActiveX

ActiveX technology was introduced in Visual Basic 5.0 for the first time. Since then it never looked back. I often hear people talking about ActiveX as some thing that is related to internet only. And some seem to think ActiveX as an advanced topic. In my sincere opinion, neither of them is true. Every Visual Basic programmer must understand what is ActiveX and how to create ActiveX components. So let us start our journey of ActiveX. But before we delve into ActiveX we need to understand the software architecture on which ActiveX is based – COM.
What is COM?
COM stands for Component Object Model. COM is software architecture that allows programmers to create components, which can be later used to build applications. The theme is reusability. To put it in other words, if you create a component using COM specifications, it can be used in any language and any platform where COM is supported.

COM is the underlying architecture that forms the foundation for higher-level software services, like those provided by OLE and ActiveX.

COM specifies the standards using which components are to be created. And the components created using COM specifications have the following characteristics:

They are platform independent. They are usable in Windows, Windows NT, Macintosh, and Unix. They are language independent. If you create a component in Visual Basic, later you can use that component in VC++, PowerBuilder or anywhere, where COM is supported.
They are also extensible.

COM is a general architecture for component software. Microsoft is using COM to address specific areas like creating controls, servers etc.

It is beyond the scope of this book to discuss about the specifications and internals of COM. There are so many technical articles in MSDN on COM and DCOM. Read them if you want to have an insight of COM.

What is ActiveX?
ActiveX is a new technology (actually a renamed technology). Its predecessor is OLE ; ActiveX allows you to create components based on COM specifications and enables you to develop interactive web pages.

ActiveX includes both client and server side technologies. That means it allows you to create components that run both on client and server.

An ActiveX component is a reusable piece of data and code (object) created using ActiveX technology. The best part of ActiveX is it allows you to create components that can be used in any project (irrespective of language) straight away. This saves a lot of development time. Well, if you boil it down, it comes to reusability, which is one of the characteristics of component software to which ActiveX belongs.

However, note that ActiveX talks about binary interoperability. That means only compiled components are reusable and NOT source code.



ActiveX Components
The components that you create using ActiveX technology are of different types. The following are the different types of ActiveX components.

ActiveX Applications (ActiveX .EXE)
An ActiveX application is a standalone application, such as MS-Word, MS-Excel etc. These applications provide objects that you can access and manipulate programmatically from an application written in Visual Basic or any application development tool that supports ActiveX.

Note: Each component has a collection of properties, methods and events that can be accessed from outside. These properties, methods and events are collectively called as interface of the component.

ActiveX Code Components (ActiveX .DLL)
ActiveX code component is a collection (library) of programmable objects, where objects are generally related to a specific topic such as, financial functions, date and time functions etc.

ActiveX code components do not run as separate applications, instead they are run in the same process area as the client (the application that is using the code component). More on this later in this chapter.

ActiveX Controls (.OCX controls)
ActiveX controls are user-defined controls. Formally they were called as OLE controls. Each ActiveX control does a specific job. For example, an ActiveX control may deal with displaying a calendar, another may deal with displaying running digital clock and so on. There are hundreds of ActiveX controls available from various vendors, whose primary job is creating ActiveX controls and sell them to developers.

Note that even Visual Basic 4.0 users could create OLE Server (now called as ActiveX Server) but creating an ActiveX control was introduced for the first time in Visual Basic 5.0. It really made Visual Basic programmers thrilled. Well, I am one of them and now you join the bandwagon.

In fact, we have already used good number of ActiveX controls, such as DataList, ADODC, DataGrid etc. We know how to use them but in the coming chapters 27, 28 & 29 we will learn how to create our own ActiveX controls.

ActiveX Document (. VBD Document)
ActiveX documents are Internet pages. You can use ActiveX documents to create interactive Internet application. Each ActiveX document is a Web page. An ActiveX document can host ActiveX controls and can invoke dialog boxes and so on.

Visual Basic 6.0 has introduced DHTML application. DHTML application provides better alternative to ActiveX document application.

In-process and Out-of-process servers
An ActiveX code component may be either in-process or out-of-process. In-process server is implemented as .DLL and out-of-process server is implemented as .EXE.

An application using ActiveX component interacts with it using Client/Server architecture. Application makes the request to the component and component responds to the request. Here client is the application that is using the services of the component. And the ActiveX component is the server. Depending upon where server runs, ActiveX components are classified into two types.

In-process server
An in-process server is an ActiveX .DLL. It runs in the address space of the client application. It cannot be run as a separate process. The communication between client (application) and server (code component) will be faster as both of them (client & server) reside in the same address space. And more importantly there is no context switch (switching from one process to another). An example for in-process server is ActiveX Data Objects library.



Out-of-process Server
An ActiveX code component that is implemented as .EXE is an out-of-process server. It runs in its own address space. When a client invokes a method of the server, control switches from client process to server process (context switch occurs). An out-of-process application can also be run as a standalone application.
Creating an ActiveX .DLL
An ActiveX DLL is a collection of object that can be used by client applications. Let us create a simple ActiveX code component that is implemented as in-process server (ActiveX .DLL).

We will create an ActiveX DLL with just one class. It is important to understand how to create a class when you are creating an ActiveX DLL, as ActiveX DLL is a collection of classes. A client application that is using this ActiveX DLL creates objects of the classes exposed by server and invokes methods and properties to get the job done.

Time Class
The ActiveX server that we are going to create contains only one class – Time class. The following is the list of properties, methods, and events of the class.

Type Name Meaning
Property Hour Sets/ returns the number of hours
Min Sets/ returns the number of minutes.
Second Sets/returns the number of minutes.
Method IncrementSecond Increments the time by one second.
SetToCurrent Sets the time to current system time.
GetTime Returns time of the class in HH: MM: SS format.
SetTime Takes time in HH: MM: SS format and changes time of the class to the given time.
Event InvalidTime Raised whenever Hour, Min, or Second property is set to an invalid value.
Table 25.1: Members of Time class.

The following are the major steps in creating an ActiveX DLL

• Create a project of ActiveX DLL type
• Create as many class modules as required.
• Change properties of project
• Create .DLL file

To creating an ActiveX DLL project:

1. Select File -> New Project and select ActiveX DLL as the type of the project.
2. Visual Basic creates a new project with a single class module with Class1 and change the name to time.
Using Class Builder utility
Class builder utility could be used to create skeleton for methods, properties and events. Let us use class builder utility to create attributes of Time class.

To invoke Class Builder Utility:

1. Select Add-In Manager option of Add-Ins Menu.
2. In Add-In Manager window double click on VB 6 Class Builder Utility
3. Then message Loaded appears under Load Behavior column.
4. Click on Ok.
5. Select Add-Ins menu and choose Class Builder Utility to invoke Class Builder.
6. If Class Builder displays a warning message, just ignore it and continue.

Renaming Class1 to Time

1. Select Class1 in Classes Pane of Class Builder Utility and click on right button.
2. Select Rename option and rename Class1 to Time.

Creating properties, methods and events using Class Builder

1. Click right button on Time class
2. Select New-> Property option from popup menu.
3. Enter the name of the property as hour and change data type to Integer.
4. In declaration group leave the Public Property radio button selected.
5. And click on Ok
At this stage class builder displays a property in the left pane.
6. Repeat the process for Min and Second properties.
7. Click right button on Time class and select New->Method from popup menu.
8. Enter IncrementSecond as the name of the method.
9. Select Attributes table and enter “Increment time by one second” as the description. Whatever description you enter here will be displayed in Object Browser when you select this method.
10. Click on Ok
11. Repeat the same process for SetToCurrent method. Enter “Sets time to current system time” as the description.
12. Again select New->Method from popup menu and enter SetTime as the name of the method and “Changes the time to the given time. Time must be given in HH: MM: SS format” as description.
13. Then click on + sign on the right of Arguments list box and enter the following details .
Name NewTime
Type String
ByVal Checked

Note: if optional checkbox is checked then the argument is optional. If no value is passed to the argument then the given default value will be stored in that.

14. Create one more method with the name GetTime and specify the Return Data Type as String.
15. Select New->Event from popup menu of Time class
16. Enter InvalidTime as the name of the event and “Fired when an given hour, min or second is invalid” as the description
At the end of creation of methods, properties and events, the class builder should look like .

Note: You can add property, method and event using icons in toolbar also.

Note: Select tab “All” if you want to see all the attributes of the class. Otherwise select one of the three tabs (Properties, Methods, and Events) to display the specific members.

To update project with changes made in class builder:

1. Select File-> Update Project option. Class builder updates the class module with the details furnished so far.
2. Exit Class builder with File-> Exit.

If you open Time class module, the code contains three properties, two methods and one event. The code is shown in listing 25.1.

'local variable(s) to hold property value(s)
Private mvarMin As Integer 'local copy
Private mvarSecond As Integer 'local copy
Private mvarHour As Integer 'local copy
'To fire this event, use RaiseEvent with the following syntax:
'RaiseEvent InvalidTime[(arg1, arg2, ... , argn)]
Public Event InvalidTime()

Public Sub SetToCurrent()
End Sub

Public Sub IncrementSecond()
End Sub

Public Property Let Hour(ByVal vData As Integer)
'used when assigning a value to the property, on the left side of an assignment.
'Syntax: X.Hour = 5
mvarHour = vData
End Property

Public Property Get Hour() As Integer
'used when retrieving value of a property, on the right side of an assignment.
'Syntax: Debug.Print X.Hour
Hour = mvarHour
End Property

Public Property Let Second(ByVal vData As Integer)
'used when assigning a value to the property, on the left side of an assignment.
'Syntax: X.Second = 5
mvarSecond = vData
End Property

Public Property Get Second() As Integer
'used when retrieving value of a property, on the right side of an assignment.
'Syntax: Debug.Print X.Second
Second = mvarSecond
End Property

Public Property Let Min(ByVal vData As Integer)
'used when assigning a value to the property, on the left side of an assignment.
'Syntax: X.Min = 5
mvarMin = vData
End Property

Public Property Get Min() As Integer
'used when retrieving value of a property, on the right side of an assignment.
'Syntax: Debug.Print X.Min
Min = mvarMin
End Property

Public Function GetTime() As String
End Function

Public Sub SetTime(ByVal newtime As String)
End Sub
Listing 25.1: Code written by Class Builder
Modifying the code written by Class Builder
Class Builder utility just creates skeleton for methods. We have to insert the code to make method operational.

GetTime Method
This method is used to return the time in HH:MM:SS format. Format function is used to get leading zero for hour, minute and second. Format function takes a values and the format using which the value is to be formatted and returns the formatted values in the form of a string. For complete details of format function, please see on-line help.

Public Function GetTime() As String
Dim s As String
' Return time in HH:MM:SS format
s =Format(Hour,"00")& ":" & Format(Min, "00")& ":" _
& Format(Second, "00")
GetTime = s

End Function
Listing 25.2: GetTime Function.

SetTime Method
Takes time in HH: MM: SS format, breaks it into hours, minutes and seconds and places them into member variables. It checks whether three values are valid. If they are not valid it raises InvalidTime event.

Public Sub SetTime(ByVal newtime As String)
Dim h As Integer
Dim m As Integer
Dim s As Integer

' input must be in HH:MM:SS format
' if values are invalid then raise INVALIDTIME event
h = CInt(Mid(newtime, 1, 2))
m = CInt(Mid(newtime, 4, 2))
s = CInt(Mid(newtime, 7, 2))
If h >= 0 And h <= 23 And m >= 0 And m <= 59 And s >= 0 And s <= 59 Then mvarHour = h mvarMin = m mvarSecond = s Else RaiseEvent InvalidTime End If End Sub Listing 25.3: SetTime method. IncrementSecond Method This method is used to increment seconds by one. If incrementing the second causes second to exceed 59 then second is set to 0 and minute is incremented by one. And so on. Public Sub IncrementSecond() ' increment second by one mvarSecond = mvarSecond + 1 If mvarSecond > 59 Then
mvarSecond = 0
mvarMin = mvarMin + 1
If mvarMin > 59 Then
mvarMin = 0
mvarHour = mvarHour + 1
If mvarHour > 23 Then
mvarHour = 0
End If
End If
End If
End Sub
Listing 25.4: IncrementSecond method.

SetToCurrent method
This is used to change time to current system time. I have used methods of DataTime object and Time function to get current hour, minute and second.

Public Sub SetToCurrent()
' change time to current system time
mvarHour = DateTime.Hour(Time)
mvarMin = DateTime.Minute(Time)
mvarSecond = DateTime.Second(Time)
End Sub
Listing 25.5: SetToCurrent method.

Property Procedures
The following are the property procedures required for Hour, Min and Second properties. In all three, if the value is assigned is not valid the InvalidTime event is raised.

Public Property Let Hour(ByVal vData As Integer)
If vData >= 0 And vdate <= 23 Then mvarHour = vData Else RaiseEvent InvalidTime End If End Property Public Property Get Hour() As Integer Hour = mvarHour End Property Public Property Let Second(ByVal vData As Integer) If vData >= 0 And vData <= 59 Then mvarSecond = vData Else RaiseEvent InvalidTime End If End Property Public Property Get Second() As Integer Second = mvarSecond End Property Public Property Let Min(ByVal vData As Integer) If vData >= 0 And vData <= 59 Then mvarMin = vData Else RaiseEvent InvalidTime End If End Property Public Property Get Min() As Integer Min = mvarMin End Property Listing 25.6: Property procedures. That is about the coding part of the class. Out ActiveX server is almost ready. Generally an ActiveX server contains more than one class. But as we are primarily interested in understanding the concept through an example, one class is quite adequate in our sample ActiveX server. Save class as name Time.Cls and project as TimeProject.VBP. Changing properties of ActiveX Server Invoke Project properties to change the properties of ActiveX server. Here are the steps to change properties. 1. Select Project -> Project Properties to invoke properties window of the current project.
2. Change Project Name to TimeServer
3. Change Project Description to “Time Class By P.Srikanth”.
4. And click on Ok.

Creating .DLL file
Now the final step. We have to create .DLL file for the project. This DLL file is used by the client application. At the time of creating .DLL file Visual Basic registers this ActiveX server in system register.

Note: All ActiveX components must be registered in the system registry. Otherwise they cannot be used in client application.

To create .DLL file:

1. Select File menu and choose Make TimeProject.dll option.
2. When you are prompted to specify the directory and the name of the file, select the directory in to which you want to place .DLL file and leave the filename to default (TimeProject).
3. Click on Ok to create .DLL file.

That is the end of creation of ActiveX in-process server. In the next section, we will see how to use this server in a client application.

Using ActiveX Server
Let us create a small project to understand how to use an ActiveX in-process server. The project type is Standard .EXE type and it contains only one form. for the user interface of the form.

Here are the steps to create testing project.

1. Start a new project using File -> New Project and select Standard Exe as the project type.
2. Invoke Form designer and place two labels and four command buttons .
3. Change the properties of the controls and form as follows.

Object Property Value
Form Caption Time Class Demo
Label1 Caption Time
Label2 Name LblTime
Caption 00:00:00
Fontsize 16
Autosize True
Borderstyle 1-Fixed Single
Command1 Name CmdSetToCurrent
Caption &Set To Current Time
Command2 Name CmdIncrement
Caption &Increment Second
Command3 Name CmdChangeTime
Caption &Change Time
Command4 Name CmdQuit
Caption &Quit

Now we need to use ActiveX server. But to use an ActiveX server, first we have to have a reference to ActiveX server in the current project.

Creating a reference to ActiveX server
Unless you create a reference to ActiveX server (or any ActiveX component), you cannot access ActiveX server. So, the first step in using an ActiveX server is creating a reference as follows:

1. Select Project - > References
Visual Basic displays the list of ActiveX servers that are registered in the system registry .
2. Search for “Time Class By P.Srikanth”. Because whatever we give as project description in ActiveX server project, that will be displayed in References window.
3. Once you locate it, check the check box on the left. Also observe that the complete path of .DLL file is placed at the bottom of the window .
4. After turning on the check box click on Ok to close References window.
Save the project as TimeTest.Vbp and form as TimeTest.Frm.

Writing code for Sample project
We have to first declare an object of Time class with WithEvents keyword. Write code for InvalidTime event of the object. And then write code for command buttons. The total code for the sample project is shown in listing 25.7.

General/Declarations

Option Explicit
'declare an object of TIME class
Dim WithEvents t As Time

Private Sub cmdChange_Click()

Dim ts As String
' take time using inputbox
ts = InputBox("Enter time in HH:MM:SS format", "Time")
If ts <> "" Then
t.SetTime ts
lbltime.Caption = t.GetTime
End If

End Sub

Private Sub cmdquit_Click()
Unload Me
End Sub

Private Sub cmdSetToCurrent_Click()
t.SetToCurrent
lbltime.Caption = t.GetTime
End Sub

Private Sub CmdIncrement_Click()
t.IncrementSecond
lbltime.Caption = t.GetTime()

End Sub

Private Sub Form_Load()
Set t = New Time
t.SetToCurrent
lbltime.Caption = t.GetTime
End Sub

Private Sub t_InvalidTime()
MsgBox "Invalid Time"
End Sub
Listing 25.7: Code for event in the form.

Test Run

1. Now run the project. As in Form_Load event Time object is set to system time, you should see the system time as soon as the project starts.
2. After some time again click on Set To Current Time command button. The time should be updated to the current system time.
3. Click on Change Time command button and enter 10:10:58 as new type. This will change the time and new time is displayed.
4. Clicking on Increment Second button should make it 10:10:59. Again clicking on it should make it 10:11:00.
5. Now again choose Change Time and enter 30:20:02 as the time. As hour portion is not valid, SetTime method of the Time class fires InvalidTime event. And you should see “Invalid Time” message in message box.

That’s all that you have to do to test whether it is working in the way you want. If you found any mistakes in Time class then open ActiveX server project, make modifications and then recreate .DLL file.