Chapter 8 ActiveX Documents

ActiveX Code Components

ActiveX Code Components earlier referred to as OLE automation Servers, provide libraries of reusable objects.  For example: A code component can include a library of specialized financial functions for spreadsheets users, or user-interface elements, like dialog boxes, that are common to multiple applications.  An object in a code component can run in the same process as our application, allowing faster access to the object.

In Visual Basic we can build code components that are in-process or our-of-process.  It provides project templates to create each type of components.

Creating An ActiveX DLL

To begin creating an ActiveX DLL we double click on the ActiveX DLL Icon in New Project dialog box.  It opens a class module ‘Class1’.  By changing its name ‘TrialDL’ in General Declaration Section of Code window a code can be written.

Example1

Private Var As String

Public Sub Greet ( )

MsgBox “Hello” & Var & “!”

End Sub

Public Property Let MyName (Name As String)

Var = UCase(Name)

End Property

Public Property Get Message ( )

Message = “This is a DLL Example”

End Property

To register DLL before calling it, the ‘Make TrialDLL.dll’ option is selected from File Menu.  So after adding Standard EXE Project, in Project Explorer, we have to set reference to TrialDLL to Form1 by selecting ‘ TrialDLL’ from references dialog box of Project Menu.

On the form place Text box and Button and write following code.

à        Private Sub Display_Click ( )

            Dim Obj As TrialDLL.Class1

            Dim StrMessage As String

            Set Obj = New Class1

            Obj.MyName = Text1.Text

Obj.Greet

StrMessage = Obj.Message

MsgBox StrMessage, , “DLL”

End Sub

An instance of the DLL is created using New keyword.  Name entered in Text Box is passed to Name property of the DLL, which converts it into Upper Case and displays message box with name in Upper Case.

StrMessage variable retrieves message from the DLL and displays it in the message box.

The Instancing Property

Instancing property of a class specifies whether we can create an object of a public class outside a project, and if so, how it will behave.  This property is not available at run time.

Setting of this property are as shown under:-

1)                  Public Not Creatable

If a component creates the objects first, only then, can applications use objects of this class.

2)                  Multi Use

Allows other applications to create objects from the class.  One instance of our component can provide any number of objects created in this fashion.

3)                  Single Use

Allows other application to create objects from the class, but every object of this class that a client creates starts a new instance of our component.

An ActiveX Document

An ActiveX Document has a dual nature.  It is a program that users can use to run all kinds of tasks from simple calculations to accessing databases across the network.

These documents have all features of a word document in the fact they can not stand alone.  i.e. they can be viewed in a container that supports them, for example Microsoft’s Internet Explorer.

Advantages of ActiveX Documents

1)                  ActiveX Documents support Hyperlink object which allows to navigate from one document to another.

2)                  ActiveX Document can be debugged using debugging tools of Visual Basic.

3)                  ActiveX Documents retain data between sessions as data is stored through the PropertyBag object.

4)                  As an ActiveX Document is loaded in a browser, Menu of the document merges with that of the browser.

User Document Object

An ActiveX document created with Visual Basic is always composed of User Document Object, code, code modules, and controls that we place on User Document.  To use an ActiveX Document we need to place it in a container that supports it.

Process of connecting ActoveX Document to it’s container is called “Siting”.  This plays a key role in determining event behavior of the ActiveX Document.

Properties of User Document Object

Hyperlink

It sets the reference to Hyperlink object.  Using methods of Hyperlink object, an ActiveX Document can request a container that is aware of hyperlinks like Microsoft Internet Explorer, to jump to a given URL which identifies full path of a document, graphic, or other file on the Internet.  Hyperlink object supports three methods which enable navigation in a browser.

Ø  Go back :      Executes a jump Back in the History List.

Ø  Go forward: Executes a jump forward in the History List.

Ø  Navigate to:   Execute a jump to the specified target

Events of User Document Object

Following are the User document objects in detail.

1)                  Init Properties

Allows to initialize a new instance of the object.  It occurs only when a new instance of an object is being created.  This is to allow the author of the object to distinguish between creating new instance of the object and loading an old instance of the object.

2)                  Initialize

Occurs when application creates an instance of an ActiveX Document.

3)                  Read Properties

Occurs when we retrieve a property from PropertyBag Object.

4)                  Terminate

Occurs when all references to an instance of an ActiveX Document are removed from memory by setting all variables that refer to object to Nothing or when the last reference to object fails out of scope.

5)                  Show

This event is triggered either when the user opens a sited document in its container or when he clicks the Back or Forward Buttons to navigate to the documents in History List of the container.

6)                  Hide

Occurs when user navigates away from current document or when container is closed before the document is closed.

Methods of User Document Object

The methods of the User Document object are as follows:

Property Changed

Notifies the container that property’s value has been changed.

Files of an ActiveX Document

Like Visual Basic forms User Document Objects have code modules and Visual Designers objects and User Document objects are stored in plain text files containing source code and property values of User Document and controls placed on it.  Visual Basic uses extension .DOB for these source files

If User document contains controls that uses graphical elements which can not be stored as a plain Text like (Bitmaps) Visual Basic stores them in a .DOX file.  Thus .DOB and .DOX files completely define an ActiveX Document’s appearance and interface.  A compiled ActiveX Document will then consist of either an ActiveX .EXE or .DLL and an accompanying .VBD file.  In a browser, User must navigate to the .VBD file to open ActiveX Document.

Compiled files

Visual Basic creates a Visual Document file having extension .VBD.  When user compile an .EXE or .DLL file the .VBD file will be placed in same directory as the compiled component.

ActiveX Document Creation

First select ActiveX document Exe in New Project dialog box. New project starts a User Document object.  We click User Document folder in Project Window and double click on User document object to display it.  After User Document object is open, place controls on it.

Except the OLE container control we can place any control on the document and then after placing controls on the document code can be written to handle any task from the document including reading or writing data in files or accessing a database.

Internet Applications

It is an interactive, compiled application that can be accessed through a corporate intranet or through the internet.

HTML (Hypertext MarkUp Language) is formatting language of the WEB.  It is not a programming and does not support variables.  The purpose of HTML is to provide instructions to web browsers on how to display the files that they download.  A .HTM file is used for this purpose.

In Visual Basic Internet Applications, content can be added to web pages.  Visual Basic code can be linked to one or more HTML pages and events raised in these pages can be effectively handled by interacting with programs on either the client or the server.  There are two main types of Visual Basic internet applications.

1)                  IIS (Internet Information Server)

Resides on a Web Server and used to process incoming requests from a browser.  IIS Applications process the requests, run associated Visual Basic Code and return responses to the users.  All processing is happens on the Server.

2)                  DHTML (Dynamic Hypertext Mark Up Language)

Most processing in a DHTML application happens on the browser computer, although the application can make calls to the server if necessary.

Introduction to DHTML

With the help of DHTML we can create interactive Web Pages depending on the user actions and requests.  Visual Basic provides a way to create DHTML applications quickly and easily.

A DHTML application is a group of HTML pages that work together to perform a process.  It enables to write Visual Basic Code to respond to actions on a HTML page, without transferring processing to the server. 

HTML pages can be created with Visual Basic through the DHTML Application.  Most of the processing  associated with a DHTML application occurs on the client computer, although application can make calls to the server.

In DHTML application, browser can process user data, make changes to page’s layout and appearance and process code without the additional contact to the server.

Creating DHTML Application

Select DHTML application from New Project dialog box.  Project starts with single page designer and code module.  Open the page designer by selecting it in Project Window.  Page designer displays two panes left and right.  Body element is displayed when document item is selected in design window.  The body element specifies beginning and end of a document and has an ID associated with it.

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