Programming Visual Basic for the Palm OS

Windows Component Implementation

We now have stub code for the TagParse component. In this section, we show how to fill in the method stubs and compile this code into a Windows DLL. Add the output files listed earlier in Table 9-9 to the ParseServer project.

Tip

It is a good idea to verify that the stub component successfully compiles before proceeding.

Smart Pointer

We use the IPtr smart pointer interface template in the implementation of the CTagParse class and ITagParse interface.^[64] A smart pointer automatically releases the interface to which it points when it goes out of scope. This alleviates some of the messy code that can accompany COM programming when an error occurs in the middle of a method, and existing interfaces need to be released before returning.

For example, in the code below, if bSuccess is set to false, we need to make sure and call Release on pMyString before returning. Otherwise, we will have a memory leak.

HRESULT MyMethod(  )
{
   IString* pMyString;
   pCoCreateString(L"MyString", &pMyString);
   bool bSuccess = true;
   //...Processing ...
   if(bSuccess == false)
   {
      pMyString->Release(  );
      return E_FAIL;
   }
   return S_OK;
}

Contrast this approach with using a smart pointer.

HRESULT MyMethod(  )
{
   IPtr<IString, &IID_IString> spMyString;
   pCoCreateString(L"MyString", &spMyString);
   bool bSuccess = true;
   //...Processing ...
   if(bSuccess == false)
      return E_FAIL;
   return S_OK;
}

Here, we can simply return E_FAIL. The smart pointer automatically calls Release on its interface when it ...