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Pre Requisites to work with the sample
Windows 2000 Sp1
.NET SDK
This sample covers the following concepts:
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Late binding to COM objects via Reflection
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Using the XmlDocument, DocumentNavigator, etc within the
System.Xml namespace to load XML files and fire XPath querries.
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Using the COM+ admin objects to talk to the COM+ catalog and query the
properties for each COM+ app installed as well as the components within them.
Motivation
I wanted to explore
the interoperability .Net provides with COM
components. What would be a better way than to test it with existing components
installed within the system. Since I already had worked with the COM+ admin
objects sometime back and not much samples are available on it, thought that
working with it in C# would be cool.
Source/Misc Files
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Descriptions
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TestComAdmin.cs
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Contains the client
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dispCOMWrapper.cs
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Contains helper classes which are compiled as
components
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build.bat
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Builds the source files |
| ComPlusPropertyMap.xml |
Contains a complete list from MSDN about the
various properties exposed by the Applications as well as the Components
collection in XML format. *See diagram below. |
Figure1 :
ComPlusPropertyMap.xml
Description
There are 2 approaches I could have taken to use these
objects:
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Use the tlbimp tool to generate equivalent .NET metadata to be used within C# or
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Late binding via IDispatch using Reflection. I chose the
latter purely to explore reflection. Using tlbimp would have been easier.
When a .NET client tries to use and instantiate a COM component, the .NET
runtime exposes the object via something called a runtime callable wrapper (RCW)
that acts as a proxy for the real unmanaged object. The .NET client is fooled in
to thinking that it is talking to just another block of managed code. The
primary function of the RCW is to marshal calls between the boundaries of the
managed and unmanaged code. For more details/diagrams on the Runtime Callable
Wrappers refer the .NET Framework SDK documentation under
.NET Framework Developer's Guide\Interoperating with Unmanaged Code\Advanced COM
Interop\COM Interop Wrappers .
Every body starts off/steals/borrows/enhances code from there.
In the example, I have create an instance of the COMAdminCatalog object
along with these lines.
Via this object I can get at the Applications' collection exposed as a COMAdminCatalogCollection
Object.
The sample comes with two helper classes dispCOMWrapper
and COMPlusAdminHelper.
The following lines uses these helper classes to print out the count of all the
COM+ apps installed on your system.
dispCOMWrapper m_oCatalog;
dispCOMWrapper m_oDispColApps;
m_oCatalog = new dispCOMWrapper("COMAdmin.COMAdminCatalog");
m_oDispColApps = new dispCOMWrapper(m_oCatalog.callMethod("GetCollection"
, new Object [] {"Applications"} ));
m_oDispColApps.callMethod("Populate",new
object [] {});
Console.Write( “Total no of COM+ applications on your system :” +
m_oDispColApps.getProperty("Count").ToString());
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There is a method known as GenerateReport() within the COMPlusAdminHelper class
that peeks in to the COM+ catalog and iterates each and every application and
then through each and every Component within it, and while it does, it generates
an XML based report in the same directory as the executable.
One can write equivalent XSL to display it in a more intuitive UI than the
default vanilla XSL that IE provides.
The
output file generated looks something like this:
Figure
2 :ComPlusReport.xml
Figure
3: The structure of the generated XML file.
To read/write/navigate xml files/nodes I
have used the following classes provided the System.Xml namespace:
XmlDocument, DocumentNavigator, XmlNode, XmlElement, XmlNamedNodeMap,
XmlAttribute.
One thing I have to admit. I found it difficult to initially move to a syntax
different than the regular MSXML syntax for firing XPath querries, but then no
choice, you gotta learn it.
Build:
Run build.bat, and then the sample.
References:
http://msdn.microsoft.com/msdnmag/issues/01/01/xml/xml.asp (From the GURU
Aaron Skonnard himself)
http://www.codeproject.com/com/complus_admin.asp (using COM+ admin objects
from VC++)
Note: Havent done much bug
testing though and not much exception handling :( Lemme know if any bugs.
And as usual as Paul Di Lascia says, If this works I am reponsible or I don't
know who the hell did it !
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