ch02.htm

用VC开发activeX控件的电子书,很不错的

ATL by itself can create small, lightweight servers that are easy
to use and modify. ATL is limited to the creation of COM-based
objects only and is lacking in generic or utility class support.
Combined with MFC and the Standard Template Library (STL), ATL
is a very powerful framework for ActiveX development. For those
developers who are willing to take the time to learn it, ATL is
by far the best route.</P> 
<P>
The BaseCtl also allows you to create small, lightweight servers.
Unfortunately, the BaseCtl lacks support from Microsoft as a product
which impacts its capability to be a practical long-term development
tool. It has, however, a very straightforward and easy-to-understand
architecture that is helpful to those developers who are learning
OLE and ActiveX from the ground up and who are not afraid of all
the gory details. <BR>
<BR>
<B>Types of Automation Servers<SPACER TYPE="HORIZONTAL" SIZE="10">
</B>When creating an Automation Server, you must decide how to
implement the server relative to how it is going to be used. You
can create two basic types of servers: DLL-based and EXE-based.
<BR>
<BR>
<I><B>DLL-based Servers<SPACER TYPE="HORIZONTAL" SIZE="10"></B></I>If
the server does not have to run as a stand-alone application and
performance is a critical issue, you should implement your server
as a DLL. A DLL-based server is typically referred to as an in-process
server because of how it normally executes relative to its controller.</P>
<P>
<I><B>EXE-based Servers <SPACER TYPE="HORIZONTAL" SIZE="10"></B></I>If
the server application does have a requirement to run as a stand-alone
application, you must implement it as an EXE. An EXE-based Automation
Server is typically referred to as a local Server or out-of-process
Server, and it will execute in its own process space. <BR>
<BR>
<B>Types of Server Execution <SPACER TYPE="HORIZONTAL" SIZE="10"></B>Automation
Servers also have an execution model that is independent of how
the server is written. Automation Servers can execute either in-process,
locally or remotely, relative to the application that has invoked
or is using it. <BR>
<BR>
<I><B>In-Process Execution <SPACER TYPE="HORIZONTAL" SIZE="10"></B></I>An
in-process Server is called <I>in-process</I> because it executes
within the same process space as that of the application that
created it. Only DLL-based automation Servers can execute as in-process,
but that is not a guarantee. This is very important to note when
using nested objects or shared objects. If an object is created
in a process space, say Process A, and it is passed to another
application in another process space, Process B, the Server in
Process A will execute as a local Server relative to the application
in Process B regardless of the fact that the Server in Process
A is a DLL-based Server. This issue is very critical since more
times than not in-process Servers are used to improve performance
of the application using them.</P> 
<P>
<I><B>Local Execution <SPACER TYPE="HORIZONTAL" SIZE="10"></B></I>Local
execution is when an Automation Server is executing in a process
space other than the process space of the controller application.
As was stated earlier, a DLL-based Server may execute locally
to its controller, depending on how it was created versus which
application is using it. The main issue with local Servers is
performance since all of the method calls have to cross process
boundaries. This condition requires additional code overhead to
move data back and forth between the Server and its Controller.</P>
<P>
<I><B>Remote Execution <SPACER TYPE="HORIZONTAL" SIZE="10"></B></I>Remote
Execution is when the Server is executing on a machine other than
the application that is controlling it. As with local Servers,
performance is an issue with this type of execution.
<H3><A NAME="Heading14">ActiveX Controls</A></H3>
<P>
An ActiveX Control, for all intents and purposes, is still the
same OCX or OLE Control that you have come to know and love over
the past several years. In fact, the only change with the coming
of ActiveX is a decrease in the requirements to qualify as a control.</P>
<P>
To qualify as an ActiveX Control, a component must be a COM Object,
implement an <TT>IUnknown</TT> interface, and support registration
and unregistration through the exported functions, DLLRegisterServer
and DLLUnregisterServer. That's it! Pretty easy, right? Well,
not really.</P>
<P>
Even though your component qualifies as an ActiveX control, if
all it supports is the preceding features, it will not do much
more than take up space on your hard disk. If it needs UI, persistence,
events, or any other feature common to controls, the control must
implement other categories of interfaces. The exact requirements
are in the <I>OLE Control and Control Container Guidelines, Version
1.1</I> published by Microsoft. All of the guidelines for ActiveX
development are available on the Internet at the Microsoft Web
site or on the ActiveX SDK CD.</P>
<P>
You have three tools at your disposal for creating ActiveX controls:
MFC, ATL, and BaseCtl. As we pointed out earlier in the section
&quot;ActiveX Automation Servers,&quot; each tool has its strengths
and weaknesses. With ActiveX Controls you only have one option
when creating and executing the control: as a DLL and in-process
to the Control's container application. Even though the extension
of the Control is .ocx, it is still in fact just a .dll.
<H2><A NAME="Heading15">Support Tools Needed for Building ActiveX
Components</A></H2>
<P>
When creating your ActiveX Components, a few tools are essential
to successful ActiveX development. Most of these tools are automatically
installed as part of the Visual C++ development environment. As
ActiveX development matures, more and more tools will become available.
Using as many tools as you can will greatly improve your understanding
of how your components work, as well as improve their overall
implementation.
<H3><A NAME="Heading16">MIDL Compiler</A></H3>
<P>
The Microsoft MIDL compiler is now a standard component of the
Microsoft Visual C++ environment. The MIDL compiler compiles COM
interface definitions (IDL) files into C code, which is then compiled
into the project by the Visual C++ compiler.</P>
<P>
The MIDL compiler also provides support for marshaling interfaces
across process boundaries. Starting with Visual C++ 4.0, the MIDL
compiler started shipping as a standard component of Visual C++.
The MIDL compiler is also available via the Win32 SDK from Microsoft.
<H3><A NAME="Heading17">Mktyplib</A></H3>
<P>
Mktyplib is a type library compiler for compiling ODL files. Mktyplib
is the predecessor to MIDL and produces the same type of output
as MIDL. The use of Mktyplib will decrease as Microsoft moves
from ODL to IDL files.
<H3><A NAME="Heading18">GUIDGEN</A></H3>
<P>
GUIDGEN is a tool that is used to generate Global Unique Identifiers
(GUID), which can be used for Interface IDs, Class IDs or any
other 128-bit UUID, such as an RPC interface. GUIDGEN is installed
only when the OLE development option is selected during the Visual
C++ installation. When GUIDGEN is run, a GUID is created and placed
in the Windows clipboard. After running the GUIDGEN application,
the resultant GUID is pasted from the clipboard into the code
that needs a GUID.
<H3><A NAME="Heading19">RegEdit</A></H3>
<P>
RegEdit, or the registration editor, is a standard component of
both the Windows 95 and Windows NT operating systems. The registration
editor is used for browsing and altering operating system and
application settings. The registration editor can also be used
for installing and registering your COM objects. <BR>
<BR>
<IMG SRC="bar.gif" WIDTH="480" HEIGHT="6" ALIGN="BOTTOM" BORDER="0"></P>
<BR>
<BLOCKQUOTE>
<B>CAUTION:<BR>
<B>RegEdit</B></B> is a very powerful tool and must be used with
extreme caution by experienced users. If used improperly, systems
can be damaged, resulting in a loss of data or a malfunctioning
computer. 
</BLOCKQUOTE>
<P>
<IMG SRC="bar.gif" WIDTH="480" HEIGHT="6" ALIGN="BOTTOM" BORDER="0">
<BR>
<BR>
In Windows 95, this program is called regedit.exe. In Windows
NT, this program is called regedt32.exe.
<H3><A NAME="Heading20">Registration Server</A></H3>
<P>
The Registration Server is an application that can be used to
register the settings of a COM object in the Windows registry
without the need to create a separate registration file. The application
is called regsvr32.exe and is automatically installed if the OLE
development option is selected during Visual C++ installation
or if the ActiveX SDK is installed.
<H3><A NAME="Heading21">Ole2View</A></H3>
<P>
Ole2View is a program that lists ActiveX components relative to
their function and category. Ole2View is extremely helpful in
the test and use of your components. Ole2View can be used to determine
whether your component is registered properly and the type and
number of interfaces your component defines. It even allows you
to instantiate and access various components and interfaces within
your application, and now it has expanded support for configuring
components to use DCOM. When attempting to determine what is the
cause of problems with a troublesome component, Ole2View is invaluable.
<H3><A NAME="Heading22">Adding the Tools to the Visual C++ Development
Environment</A></H3>
<P>
In order to maximize development productivity, the tools needed
for COM programming should be integrated into the Visual C++ environment.
Each of the tools needed can be added to the IDE's (Integrated
Development Environment) <U>T</U>ools menu. The following section
illustrates how to incorporate the tools into the IDE.</P>
<P>
Adding GUIDGEN to the Visual C++ environment enables the generation
of a UUID from a single menu command. The generated UUID is placed
in the Windows clipboard and must be pasted into the project code.</P>
<P>
To add GUIDGEN to the Visual C++ environment: 
<OL>
<LI>Select the <U>C</U>ustomize command from the <U>T</U>ools
menu. Select the Tools tab from the Customize dialog. <BR>
<LI>In the <U>M</U>enu Contents list box, scroll to the bottom
of the list, and select a blank line, and type <B>&amp;Generate
New UUID</B>. <BR>
<LI>In the Command edit box, type <B>GUIDGEN.EXE</B>. <BR>
<LI>Clear all text from the <U>A</U>rguments edit box. <BR>
<LI>Clear all text from the <U>I</U>nitial Directory edit box.
<BR>
<LI>Click the Close button to add the entry to the Tools menu.
</OL>
<P>
In addition to the GUIDGEN program, you may want to consider adding
the registry editor, the ability to unregister a component, and
any other tool that you find useful for your development.
<H2><A NAME="Heading23">From Here...</A></H2>
<P>
All of the frameworks described in this chapter have their strengths
and weaknesses. MFC allows for rapid component creation and implementation
and the level of support built into the VC++ IDE for MFC is beyond
comparison with ATL or BaseCtl. MFC offers a very large and robust
class library for solving most, if not all, of your development
problems. MFC does, however, suffer from the problem that it is
everything to everyone, which results in a slower application
or one that cannot deviate from the &quot;norm&quot; fairly easily.</P>
<P>
ATL provides a small and deliberate framework for creating ActiveX
components. ATL, however, falls very short in the area of common
class and utility support, which is the thing that is MFC's strength.
In addition, ATL's integration with the VC++ IDE also leaves room
for improvement.</P>
<P>
BaseCtl is similar to ATL in that it is focused specifically on
small, fast component development. Like ATL, it lacks the same
common class and utility support that makes MFC so attractive.
BaseCtl has an added negative of being considered only as a sample
and not as a supported product by Microsoft.</P>
<P>
The level of experience of the development team and the intended
life cycle of the code and applications will also affect the decision
of which tool to choose to create ActiveX components. Take the
time to investigate all of the options available to you before
deciding on a platform and a direction.</P> 
<P>
The following chapters examine in detail how to implement some
of the components described so far using MFC, ATL, and BaseCtl.
Even with all of the information presented so far, the only true
way to know that you have made the right choice is to do it yourself.</P>
<HR>
<P>
<CENTER></P><FONT SIZE=1>&copy; 1997, QUE Corporation, an imprint
of Macmillan Publishing USA, a Simon and Schuster Company.</P></FONT>
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