The MFC wizard does not generate code for the methods that take a BYTE or BYTE* as a parameter

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This article was previously published under Q241862

SYMPTOMS

When generating wrapper classes for a COM server that has methods that take a BYTE or BYTE* as a parameter, the MFC wizards do not generate code for these methods. The wizard does place a comment in the wrapper class header file that states that the method was not emitted due to an invalid return type or parameter type. Following is the exact text:

// Operations
public:
// method 'PassByte' not emitted because of invalid return type or parameter type

BYTE and BYTE* are both OLE Automation compatible data types, thus this message can be somewhat confusing.

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CAUSE

This is due to bugs in ClassWizard and Component Gallery not recognizing BYTE and BYTE* as valid OLE Automation data types.

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RESOLUTION

You can add the methods that were omitted manually. For example, given a method PassByte that takes a single BYTE parameter and another method PassBytePointer that takes a single BYTE* parameter, you could add the following code to the wrapper class in the wrapper class header file as follows:

// Operations
public:
// method 'PassByte' not emitted because of invalid return type or parameter type
   void PassByte(BYTE byteVal);

// method 'PassBytePointer' not emitted because of invalid return type or parameter type
   void PassBytePointer(BYTE *pbyteVal);

Next, you need to add the code to the wrapper class source file. Given the example above, it should look like the following:

#define MY_VTS_UI1 "\x11"
//Do NOT use VTS_UI1. It has a value of "0x0F" which is incorrect.
//The correct value for VT_UI1 is 17 or 0x11

#define MY_VTS_PUI1 "\x51"
//Do NOT use VTS_PUI1. It has a value of "0x4F" which is incorrect.
//The correct value for VT_PUI1 is 81 or 0x51

void C_UserControl1::PassByte(BYTE byteVal)
{
 static BYTE parms[] = MY_VTS_UI1; //please note that this is not VTS_UI1

 DISPID dispid = 0x60030000;
 InvokeHelper(dispid, DISPATCH_METHOD, VT_EMPTY, NULL, parms, byteVal);
}

void C_UserControl1::PassBytePointer(BYTE *pbyteVal)
{
 static BYTE parms[] = MY_VTS_PUI1; //please note that this is not VTS_PUI1

 DISPID dispid = 0x60030001; //notice that this is different!
 InvokeHelper(dispid, DISPATCH_METHOD, VT_EMPTY, NULL, parms, pbyteVal);
}

It is important to note that you need to get the DISPIDs for the omitted methods using a type library viewing tool. OLE/COM Object Viewer is one such tool. You can access this tool from the Tools menu in Visual C++. In OLE/COM Object Viewer, select the File menu and the View Typelib menu item. Next, find the .tlb or .ocx file for the COM server and click Open. This opens a new window with a tree control on the left side. Select the topmost item in the tree control and you will see all of the methods on the right with their corresponding DISPID's.

A second important point is that VTS_UI1 and VTS_PUI1 are not used above. For more informationon this bug, click the following article number to view the article in the Microsoft Knowledge Base:

242588 (http://support.microsoft.com/kb/242588/ ) VTS_U1 and VTS_PUI1 are defined incorrectly in the AfxDisp.h header file

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STATUS

Microsoft has confirmed that this is a bug in the Microsoft products that are listed at the beginning of this article.

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MORE INFORMATION

Steps to reproduce the behavior

Create a new Visual Basic ActiveX control.

Add one method that takes a BYTE parameter. For example:

Public Sub PassByte(ByVal b as Byte)
End Sub

Build the control.
Create a new MFC Dialog based application.
Add the Visual Basic control that was generated in step 3 using Component Gallery. Do this by going to the Project menu, select Add Components and Controls, and then selecting Registered ActiveX Controls.
After you select the Visual Basic control and click OK, Component Gallery presents the Confirm Classes dialog. Click OK on the Confirm Classes dialog box to generate the wrapper code.

To see the missing method, open up the generated wrapper class header file. You should see the text that states the method PassByte was not emitted because of invalid return type or parameter type.

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