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<TITLE>Special Edition Using Visual C++ 6 -- Ch 13 -- ActiveX Concepts</TITLE>
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Special Edition Using Visual C++ 6</H1>
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<H1>- 13 -</H1>
<H1>ActiveX Concepts</H1>
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<UL>
<LI><A HREF="#Heading1">The Purpose of ActiveX</A>
<LI><A HREF="#Heading2">Object Linking</A>
<LI><A HREF="#Heading3">Object Embedding</A>
<LI><A HREF="#Heading4">Containers and Servers</A>
<LI><A HREF="#Heading5">Toward a More Intuitive User Interface</A>
<LI><A HREF="#Heading6">The Component Object Model</A>
<LI><A HREF="#Heading7">Automation</A>
<LI><A HREF="#Heading8">ActiveX Controls</A>
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<H2><A NAME="Heading1"></A>The Purpose of ActiveX</H2>
<P>This chapter covers the theory and concepts of ActiveX, which is built on the
Component Object Model (COM). Until recently, the technology built on COM was called
OLE, and OLE still exists, but the emphasis now is on ActiveX. Most new programmers
have found OLE intimidating, and the switch to ActiveX is unlikely to lessen that.
However, if you think of ActiveX technology as a way to use code already written
and tested by someone else, and as a way to save yourself the trouble of reinventing
the wheel, you'll see why it's worth learning. Developer Studio and MFC make ActiveX
much easier to understand and implement by doing much of the groundwork for you.
There are four chapters in Part V, "Internet Programming," and together
they demonstrate what ActiveX has become. In addition, ActiveX controls, which to
many developers represent the way of the future, are discussed in Chapter 20, "Building
an Internet ActiveX Control," and Chapter 21, "The Active Template Library."
These are best read after Chapters 18 and 19.</P>
<P>Windows has always been an operating system that allows several applications running
at once, and right from the beginning, programmers wanted to have a way for those
applications to exchange information while running. The Clipboard was a marvelous
innovation, though, of course, the user had to do a lot of the work. DDE (Dynamic
Data Exchange) allowed applications to "talk" to each other but had some
major limitations. Then came OLE 1 (Object Linking and Embedding). Later there was
OLE 2, and then Microsoft just called it OLE, until it moved so far beyond its original
roots that it was renamed ActiveX.</P>
<BLOCKQUOTE>
<P>
<HR>
<strong>NOTE:</strong> Experienced Windows users will probably be familiar with the examples
presented in the early part of this chapter. If you know what ActiveX can do for
users and are interested in why it works jump ahead to the "Component Object
Model" section, which looks under the hood a little. n
<HR>
</BLOCKQUOTE>
<P>ActiveX lets users and applications be document-centered, and this is probably
the most important thing about it. If a user wants to create an annual report, by
choosing ActiveX-enabled applications, the user stays focused on that annual report.
Perhaps parts of it are being done with Word and parts with Excel, but, to the user,
these applications are not really the point. This shift in focus is happening on
many fronts and corresponds to a more object-oriented way of thinking among many
programmers. It seems more natural now to share work among several different applications
and arrange for them to communicate than to write one huge application that can do
everything.</P>
<P>Here's a simple test to see whether you are document centered or application centered:
How is your hard drive organized?</P>
<P>The directory structure in Figure 13.1 is application centered: The directories
are named for the applications that were used to create the documents they hold.
All Word documents are together, even though they might be for very different clients
or projects.</P>
<P><A HREF="javascript:popUp('13uvc01.gif')"><B>FIG. 13.1</B></A><B> </B><I>An application-centered
directory structure arranges documents by type.</I></P>
<P>The directory structure in Figure 13.2 is document centered: The directories are
named for the client or project involved. All the sales files are together, even
though they can be accessed with a variety of different applications.</P>
<P><A HREF="javascript:popUp('13uvc02.gif')"><B>FIG. 13.2</B></A><B> </B><I>A document-centered
directory structure arranges documents by meaning or content.</I></P>
<P>If you've been using desktop computers long enough, you remember when using a
program involved a program disk and a data disk. Perhaps you remember installing
software that demanded to know the data directory where you would keep all the files
created with that product. That was application-centered thinking, and it's fast
being supplanted by document- centered thinking.</P>
<P>Why? What's wrong with application-centered thinking? Well, where do you put the
documents that are used with two applications equally often? There was a time when
each product could read its own file formats and no others. But these days, the lines
between applications are blurring; a document created in one word processor can easily
be read into another, a spreadsheet file can be used as a database, and so on. If
a client sends you a WordPerfect document and you don't have WordPerfect, do you
make a \WORDPERFECT\DOCS directory to put it in, or add it to your \MSOFFICE\WORD\DOCS
directory? If you have your hard drive arranged in a more document-centered manner,
you can just put it in the directory for that client.</P>
<P>The Windows 95 interface, now incorporated into Windows NT as well, encourages
document-centered thinking by having users double-click documents to automatically
launch the applications that created them. This wasn't new--File Manager had that
capability for years--but it feels very different to double-click an icon that's
just sitting on the desktop than it does to start an application and then double-click
an entry in a list box. More and more it doesn't matter what application or applications
were involved in creating this document; you just want to see and change your data,
and you want to do that quickly and simply.</P>
<P>After you become document-centered, you see the appeal of <I>compound documents</I>--files
created with more than one application. If your report needs an illustration, you
create it in some graphic program and then stick it in with your text when it's done.
If your annual report needs a table, and you already have the numbers in a spreadsheet,
you don't retype them into the table feature of your word processor or even import
them; you incorporate them as a spreadsheet excerpt, right in the middle of your
text. This isn't earth-shatteringly new, of course. Early desktop publishing programs
such as Ventura pulled together text and graphics from a variety of sources into
one complex compound document. What's exciting is being able to do it simply, intuitively,
and with so many different applications.</P>
<P>
<H2><A NAME="Heading2"></A>Object Linking</H2>
<P>Figure 13.3 shows a Word document with an Excel spreadsheet linked into it.</P>
<P>Follow these steps to create a similar document yourself:</P>
<P>
<DL>
<DD><B>1. </B>Start Word and enter your text.
<P>
<DT></DT>
<DD><B>2. </B>Click where you want the table to go.
<P>
<DT></DT>
<DD><B>3. </B>Choose Insert, Object.
<P>
<DT></DT>
<DD><B>4. </B>Select the Create from File tab.
<P>
<DT></DT>
<DD><B>5. </B>Enter or select the filename as though this were a File Open dialog
box.
<P>
<DT></DT>
<DD><B>6. </B>Be sure to check the Link to File box.
<P>
<DT></DT>
<DD><B>7.</B> Click OK.
</DL>
<P>The entire file appears in your document. If you make a change in the file on
disk, the change is reflected in your document. You can edit the file in its own
application by double-clicking it within Word. The other application is launched
to edit it, as shown in Figure 13.4. If you delete the file from disk, your Word
document still displays what the file last looked like, but you aren't able to edit
it.</P>
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