qr code generator asp net c# The TypeDemo window in Visual C#.NET

Drawer QR-Code in Visual C#.NET The TypeDemo window

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COM components can easily be consumed in a .NET application, although the reasons for doing so need to be carefully considered. You can use the COM tab of the Add Reference dialog box to add a reference to registered COM components. The TlbImp.exe tool is a command-line mechanism to import a COM component. The out switch of the TlbImp.exe tool can be used to change the name of the assembly that will be imported from its original name to a preferred one. The default behavior when catching System.Exception objects now catches both CLS-compliant and non-CLS-compliant exceptions. The RuntimeCompatibilty attribute can be used to change whether non-CLScompliant exceptions will be trapped by default.

You can use the following questions to test your knowledge of the information in Lesson 1, Using COM Objects. The questions are also available on the companion CD if you prefer to review them in electronic form.

Answers to these questions and explanations of why each answer choice is right or wrong are located in the Answers section at the end of the book.

1. Which methods allow COM components to be used in .NET applications (Choose all that apply.) A. Add a reference to the component through Microsoft Visual Studio 2005. B. Use the Type Library Import tool (TlbImport.exe). C. Use the Regsvr32 tool. D. Ensure that the application is registered, using the RegSvr tool if necessary. Then either add a reference to it from the COM tab of the Add Reference dialog box or use TblImp.exe. 2. How should non-CLS-compliant exceptions be trapped when running under the .NET Framework 2.0 (Choose all that apply.) A. Trap an instance of the ApplicationException.

B. Trap an instance of System.Exception, and set the RuntimeCompatibilty attribute to false. C. Simply trap an instance of a System.Exception object. D. Trap an instance of System.Exception, and set the RuntimeCompatibilty attribute to true. 3. Which items are generally considered shortcomings associated with using COM Interop (Choose all that apply.) A. Lack of support for Shared members (in Visual Basic) and Static members (in C#) B. Inability to use parameterized constructors C. Limited portability between different operating systems D. Limited ability to use inheritance hierarchies 4. Which tools can be used to manipulate COM Interop (Choose all that apply.) A. Intermediate Language Disassembler (Ildasm.exe). B. The .NET Framework 2.0 Configuration Tool. C. Type Library Importer (TlbImp.exe). D. The Windows Registry Editor.

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So far, we ve focused on getting at COM data from within a .NET context. Now we re going to examine the mirror opposite, exposing .NET components to COM.

After this lesson, you will be able to:

Build a .NET component that can be consumed by COM Hide public data from COM components Deploy COM-enabled assemblies

Just as COM components can be consumed by .NET applications, the reverse is true. When .NET components are consumed by COM, a proxy known as a COM Callable Wrapper (CCW) handles marshaling items between .NET and COM.

No matter how many COM clients consume a given managed object, the .NET runtime will create only one CCW.

There s one additional step that needs to be performed for components that will be consumed by COM versus ones that won t. To accomplish this task from start to finish, perform the following steps: 1. Create a .NET class library just like you normally would. 2. Open the Project Properties dialog box by right-clicking the project and selecting Properties. 3. Click the Build tab, which is located on the right side of the dialog box. 4. Select the Register For COM Interop option in the Output section of the tab, as shown in Figure 13-3. 5. Build the application.