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Showing posts with the label COM

Limitations of COM Interop

Following is the list of some shortcomings: Static/shared members: COM objects are fundamentally different from .Net types. One of the differences is lack of support for static/shared members. Parameterized Constructors: COM types don't allow parameters to be passed into a constructor. This limits the control you have over initialization and the use of overloaded constructors. Inheritance: One of the biggest issues is the limitations COM objects place on the inheritance chain. Members that shadow members in a base class aren't recognizable, and therefore, aren't callable or usable in real sense. Portability: Operating Systems other than Windows don't have registry. Reliance on Windows registry limits the number of environments a .Net application can be ported to.

Optional Parameter issue with COM and C#/VB

As we all know, C# doesn't support optional parameters(till framework 3.5) whereas VB does.In the same way, COM components don't support parameter overloading , so for each value in a parameter list, we've got to pass in something, even if it does nothing. Moreover, COM parameters are always passes by reference , which means we can't pass NULL as a value. In VB 2005, this is not really as issue because it supports optional parameters and we can just leave them out. But C# doesn't support this, so one have to create object variables and pass them in. See following code sample: u sing Microsoft.Office.Core; u sing Microsoft.Office.Interop.Excel;  // Must have office installed Application NewExcelApp = new Application; NewExcelApp.Worksheets.Add();       // This will not compile So, as a workaround, the Type.Missing field can be used and this field can be passed in with the C# code and the application will work as expected.  Check it in below code sni