PRB: Wrapper Class for Automation Object May Be Incomplete

ID: Q152073

The information in this article applies to:

The ClassWizard, included with:
- Microsoft Visual C++, 32-bit Editions, versions 2.0, 2.1, 2.2, 4.0, 4.1

SYMPTOMS

An automation object may support a statement and function with the same name even though the statement and function will most likely have different behaviors. Class Wizard will not recognize both the statement and function. However, when generating a new class from the object's type library, the Class Wizard will generate a function and prototype for a single function. This generated function will not give you the ability to call both the function and the statement.

CAUSE

The similarly-named function and statement will share a single entry in the .odl file for the object and a single entry in the type library. The Class Wizard does the best job it can and generates a single function and prototype based on this entry.

RESOLUTION

Given adequate documentation for the statement and function, it is possible to modify the wrapper class by hand so that the statement or function may be called. If the parameter list for the statement and function vary, which may be the case if optional parameters are used, the wrapper function can be overridden. Otherwise, the wrapper for the statement and function will need different names.

STATUS

This behavior is by design.

MORE INFORMATION

An example of this problem is WordBasic's Bold. The Bold statement turns the bold character formatting on and off just as selecting the Bold Toolbar button in Word does. The Bold() function returns a short indicating whether all, some, or none of the characters in a selection are formatted as bold. Visual Basic will call the function if a return value is assigned to the Bold() call. Otherwise, it will call the Bold statement.

The .odl statement for Bold is as follows:


   [id(0x00008048), helpstring("Makes the selection bold (toggle)"),
   helpcontext(0x00001d48)] short Bold([in, optional] VARIANT On);

The Class Wizard will generate the following function and prototype using this information:


   short Bold(const VARIANT& On);

   short WordBasic::Bold(const VARIANT& On)
   {
       short result;
       static BYTE parms[] =
           VTS_VARIANT;
       InvokeHelper(0x8048, DISPATCH_METHOD, VT_I2, (void*)&result, parms,
           &On);
       return result;
   }

Using this function will result in the WordBasic Bold() function being called. In order to call the statement, you could define BoldStatement() and BoldFunction() functions. In this case, however, because there is no reason to pass a parameter to the Bold() function, the parameter lists vary and it is possible to overload the wrapper functions as follows:


   void Bold(const VARIANT& On);
   short Bold();

   void WordBasic::Bold(const VARIANT& On)
   {
       static BYTE parms[] =
           VTS_VARIANT;
       InvokeHelper(0x8048, DISPATCH_METHOD, VT_EMPTY, NULL, parms,
           &On);
   }

   short WordBasic::Bold()
   {
       short result;
       static BYTE parms[] =
           VTS_VARIANT;
       InvokeHelper(0x8048, DISPATCH_METHOD, VT_I2, (void*)&result, NULL);
       return result;
   }

REFERENCES

Microsoft Office Developer's Kit - PART 2 Word Basic Reference, Statements and Functions.

Additional query words: 2.00 2.10 2.20 4.00 4.10 automation variant

Keywords : kbole kbMFC kbVC
Version : 2.00 2.10 2.20 4.00 4.10
Platform : NT WINDOWS
Issue type :