Library tutorials & articles
COM Interoperability in .NET Part 1
G.Gnana Arun Ganesh is the Administrator and the Founder of ARUN MICRO SYSTEMS (www.arunmicrosystems.netfirms.com). He has been programming in C++, Visual Basic, COM, Java and Microsoft Technologie...
- Introduction
- The .NET and COM Mediator
- The .NET Code
The .NET and COM Mediator
.NET runtime affords COM Interoperability wrapper for overcoming the differences between .NET and COM environments. For example, runtime make an instance of COM Callable Wrapper (CCW) when a COM client accesses a .NET component. In the same way, an instance of Runtime Callable Wrapper (RCW) is formed when a .NET client accesses a COM component. These wrappers abstract the dissimilarity and provide the faultless incorporation between the two environments.
Platform Invoke:
The platform invoke services offers a method to call functions that are exported from an unmanaged DLL. The most distinctive use of PInvoke is to allow .Net components to interact with the Win32 API. PInvoke is also used to access functions exports defined in custom DLLs.
To exemplify the use of PInvoke I create a C# class that makes a call to theWin32 Message Box () function. Before we move into the C# class let us see an example program in VB 6.
The C prototype :
int MessageBox(Hwnd hwnd,
LPCTSTR lpText,
LPCTSTR lpCaption,
UINT uType);
Parameters
hwnd ---> Handle to the dialog's owner.
lpText ---> The text you wish to display
lpCaption ---> The caption of the message box.
wType ---> The dialog definition. Ex: vbYesNo
Returns ---> Returns the value of the button that was clicked.
VB Declaration:
Private Declare Function MessageBox Lib "user32" Alias
"MessageBoxA"_
(ByVal hwnd As Long, ByVal lpText As String, ByVal lpCaption As String,_
ByVal wType As Long) As Long
Private Sub Command1_Click()
Dim ar As Long
ar = MessageBox(hwnd, "Msgbox using API", "Arungg", vbInformation)
End Sub
In the above example program, I show you how you can use the Windows API in Vb 6. The Visual Basic MsgBox() function actually wrap the MessageBox API. You don't need to use this API; in fact, it would just be unnecessary work. However to understand the usage of API, I show you the above example.
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