- Special Edition Using Visual Basic Script -

CHAPTER 10 - Embedding Internet Explorer in Your Application

by Ibrahim Malluf

While Internet Explorer is a complete standalone application, it is also an OLE Automation Server and a COM object. This means that you can use the Internet Explorer as an object in your programs from which you can instantiate and manipulate through its automation interface. If you are a VB or C++ programmer, you can also utilize the WebBrowser object contained within the shdocvw.dll as the foundation for your own customized browser.

In this chapter

• Control Internet Explorer 3.0
• You'll be prepared to use Internet Explorer as an application object.
• Build your own browser
• After you've read this chapter, you'll be ready to construct your own Web browser.

Controlling the Internet Explorer 3.0 Application as an Application Object

While you could use the VB Shell command to call up the Internet Explorer as a separate application, controlling the Internet Explorer application through OLE automation is a more appropriate approach that gives you direct access to many properties and methods of the InternetExplorer object. In this chapter, Visual Basic 4 will be used to present a very easy example of automating the Internet Explorer through a Visual Basic application.

To lay out the form, do the following:

1. Start a new Visual Basic project and save it with the name IEControl.vbj.

2. Add a text box and an array of eight command button controls with the name cmdBrowser for the command controls. Arrange them as shown in Figure 10.1.

FIG. 10.1

This Internet Explorer automation project is being created in Visual Basic 4.

3. From the tools menu of the Visual Basic menu, select the Custom Controls menu item.

4. From the list of custom controls, select the Microsoft Internet and Shell controls.

5. In the General Declarations area of the QueDemo form, add the declaration of the automation server, "Private MyIE as New InternetExplorer." This creates an instance of the Internet Explorer as an OLE automation server within your project. To complete this example, enter the code in Listing 10.1

Listing 10.1 quedemo.frmùProgramming the methods and properties of the Internet Explorer

When the project is run, the QueDemo form is displayed, giving the user eight actions to select. By clicking the Open Explorer button, a fully operational instance of the Internet Explorer will be displayed. The user can manipulate the Explorer from either the Internet Explorer itself or from the project form. If the user ends the Internet Explorer from the Explorer's interface, an automation error occurs. You will also get an automation error when trying to go back or forward when there are no pages to go back or forward to. Using this method to provide Internet browsing to your applications is very limited but allows quick implementation. If you are looking for something a little more robust, read on.

Building Your Own Browser

The shdocvw.dll exposes a control called the WebBrowser that can be dropped on your application's form and provides a set of events, properties, and methods that gives you almost complete control over your Web browsing. In this section, we'll build the shell of a browser application that can be easily customized to meet organizational requirements for functionality, security, and so on. Table 10.1 is a table of controls to be placed on the form.

Table 10.1 Controls to Place on the Project Form

Arrange the controls on the frmBrowser.frm as shown in Figure 10.2. In the case of the WebBrowser control, make it a child of the WebContainer picture box control by first selecting the picture box and then drawing the WebBrowser control into it. The txtAddress and cmbAddress controls can be placed anywhere since they will be sized and moved into place by program code anyway. The status bar should have three panels with the last two panels having their Styles set to Date and Time respectively.

FIG. 10.2

Where do the browser project controls go?

For the ToolBar control, set the button properties as shown in Table 10.2.

Table 11.2 The Button Property settings for the MyTools ToolBar

At this point, there should be a form with all of the required controls with properties set up properly. I should make it clear here that when this project hasbeen completed, you will have a working browser, but it is not any where nearcomplete enough for distribution and is only a vehicle to demonstrate what can be accomplished. You will have to flesh this project out with appropriate error handling, user interface, and other enhancements by yourself. Included on the CD is a file called clsToolBox.cls that contains some utility procedures that the project requires. Add this file to the project now.

There are two public properties exposed by this form, the Location and ShowStatus properties as shown in Listing 10.2. While not used anywhere in this project, they are included so that you can easily add this form and its supporting clsToolBox class to another project. You can also add other public properties and methods as needed. By setting the Location property to a valid URL, you can cause the results of that URL to be displayed in this form. The ShowStatus properties allow you to read and write to the form's status bar.

Listing 10.2 frmbrowser.frmùThe General Declarations and Property Procedures of the frmBrowser Form

The next group of procedures are general procedures that provide supporting code to the events triggered by the user or by the browser. The first procedure in Listing 10.3 is the GetDocumentFile() function that returns a Boolean True if the user selected a file and a False if the user cancels. If the function returns a True, then the file path is returned through the function's strFileName argument. The ResizeAll sub procedure maintains the sizing of all of the controls as the user resizes the form or as the WebBrowser control changes size due to URL parameters. We call this procedure from the form's Resize event and from the WebBrowser's MyWeb_OnDownloadBegin() event. This gives the WebBrowser an ugly flicker when a given URL is acted upon, but it was the only solution available with the beta release Internet Explorer 3.0. The final release of Internet Explorer 3.0 is supposed to include an OnWindowResized event that shows some interesting possibilities, but it was not functional as this book went to press.

Listing 10.3 frmbrowser.frmùThe General Procedures Code

The last procedure in Listing 10.3 is the AddToList() subroutine. Its purpose is to check the URLs contained in the ComboBox passed as an argument to it for duplicates. If there are no duplicates, it adds the URL to the list. Also if the list has exceeded 20 entries, it removes an entry from the list to keep it at the maximum 20 entries. The subroutine calls a utility procedure from the clsTools object called IsExactComboMatch().

Listing 10.4 contains the event code for the form. The Load Event of the frmBrowser sets the form's caption, adds a URL to the cmbAddress ComboBox, and displays the browser's home page as determined by Internet Explorer's system settings.

Listing 10.4 frmbrowser.frmùThe From Events Code for the frm.Browser

The form's Resize event calls the ResizeAll() procedure as long as the form's window state is not transitioning to the minimized state. If the ResizeAll() procedure was called with a minimized window, then invalid property errors occur. Finally,being a hopeless paranoid and knowing the OS is out to get me, I make sure that I terminate the clsTools object by setting the object reference to nothing.

Moving on to the cmbAddress and MyTools events, we have Listing 10.5.

Listing 10.5 frmbrowser.frmùThe Event Procedures for the cmbAddress and Mytools Controls

The cmbAddress KeyPress() event checks for a carriage return signaling the end of input and the desire to activate the URL and load the Web browser. The MyTools_ButtonClick event provides the navigational tools that allow you to go back, forward, home, or refresh the HTML document displayed. If you attempt to navigate to a page that doesn't exist (no next or previous page), an error is generated. Those errors are trapped here and displayed in a message box. They are not fatal errors and merely need to be trapped to prevent program crashes.

Now we can get to the WebBrowser's events. In the beta version of the Internet Explorer, several of the events were not yet functional, but enough were working that I could make a substantial browser application. Listing 10.6 provides the event code for the WebBrowser control.

Listing 10.6 frmbrowser.frmùThe Event Code for the WebBrowser Control

In the MyWeb_OnDownloadBegin() event, the ResizeAll procedure is called to counteract the fact that loading a new URL causes the WebBrowser control to be resized to accommodate the size of the HTML document. The ResizeAll procedure provides the mechanism to pull the WebBrowser's size back into conformity with the size of its container, the PictureBox control. In the MyWeb_OnNavigate() and MyWeb_OnDownloadComplete() events, the mouse pointer is manipulated to let the user know that something is happening. In the MyWeb_OnStatusTextChange() event, the user is notified of the WebBrowser's status through the status bar control.

One limitation here is that the WebBrowser control does not return any text indicating when the mouse pointer is positioned over a link. All the code is now in place to run the WebBrowser project. Press F5 to run the project. It should look like Figure 10.3.

FIG. 10.3

Here's the WebBrowser project running.

We have created a minimal Web browser. What can be done with it? Let's take a situation where we only want the users within our organization to have limited access to the Internet. We want to limit this access to the Microsoft.com site for the purposes of research. We don't want anyone cruising the net for entertainment on our time. So built into our organization's browser is code that allows free navigation within Microsoft's environment but not anywhere else. Listing 10.7 adds this functionality.

Listing 10.7 frmbrowser.frmùLimiting the Browser's Internet Scope

All I am doing here is checking the URL for microsoft.com and canceling the navigation event if not found. This is a very simplistic example and should be fleshed out with a little more sophistication that reflects your needs. When the navigation is canceled in this manner, the Web browser generates an error event in the procedure that called the navigate method. You will have to add error-handling code to address this error. Listing 10.8 shows the two relevant procedures in this project modified to handle this error.

Listing 10.8 frmbrowser.frmùAdding Error Code to Compensate for the Navigation Method Being Canceled

From Here...

In the release version of the Internet Explorer there will be more Events wired in and working to give you greater control of the WebBrowser control. Internet Explorer gives you the ability to create custom browsers that fit the exacting needs of an organization's environmentùfrom the corporate intranet to Internet access for students in high-school classrooms. We did not show examples of VBScript and Visual Basic interacting with each other here because the Document Object was not functional at the time of this writing. Be sure to watch the Web site related to this book for examples.