Selecting ltmmPlay Object Renderers for C

The following example shows how to enumerate and select ltmmPlay object renderers.

// define helper macros for using interfaces under C
#define COBJMACROS

#include "ltmm.h"
#include "resource.h"
#include "tchar.h"
#include "stdio.h"

HINSTANCE g_hInstance; // application instance handle
IltmmPlay* g_pPlay; // convert object's interface pointer

//
// BuildRendererList
// fills a listbox to match the contents of the collection
//
// pRenderers = renderer collection's interface pointer
// hwndListBox = listbox window handle
//
void BuildRendererList(IltmmRenderers* pRenderers, HWND hwndListBox)
{
   long i;
   long count;
   int selected = -1;

   // reset the listbox contents
   SendMessage(hwndListBox, LB_RESETCONTENT, 0, 0);

   // get the collection's item count
   IltmmRenderers__get_Count(pRenderers, &count);

   for(i = 0; i < count; i++)
   {
      IltmmRenderer* pRenderer;
      BSTR bstr;
      TCHAR sz[256];
      int index;
      VARIANT_BOOL f;

      // retrieve collection item
      IltmmRenderers_Item(pRenderers, i, &pRenderer);
   
      // get displayable name
      IltmmRenderer__get_FriendlyName(pRenderer, &bstr);

      // convert from unicode
      _stprintf(sz, _T("%ls"), bstr);

      // free name
      SysFreeString(bstr);

      // add the name to the listbox
      index = SendMessage(hwndListBox, LB_ADDSTRING, 0, (LPARAM) (LPCTSTR) sz);

      // associate the listbox item with the collection item index
      SendMessage(hwndListBox, LB_SETITEMDATA, index, i);

      // remember this listbox item, if it is selected in the collection
      IltmmRenderer__get_Selected(pRenderer, &f);
      if(f)
         selected = i;
   
      // free the collection item
      IUnknown_Release(pRenderer);
   }

   // select the appropriate listbox item
   for(i = 0; i < count; i++)
   {
      if(selected == (long) SendMessage(hwndListBox, LB__getITEMDATA, i, 0))
      {
         SendMessage(hwndListBox, LB_SETCURSEL, i, 0);
         break;
      }
   }

}

//
// RendererSelectionChanged
// called to reflect changes in the listbox selection
//
// pRenderers = renderer collection's interface pointer
// hwndListBox = listbox window handle
//
void RendererSelectionChanged(IltmmRenderers* pRenderers, HWND hwndListBox)
{
   int index;
   long item;
   int i;
   int count;
   HRESULT hr;

   // get the index of current listbox selection
   index = (int) SendMessage(hwndListBox, LB__getCURSEL, 0, 0);
   
   if(index < 0)
   {
      // clear selection
      IltmmRenderers__put_Selection(pRenderers, -1);
   }
   else
   {

      // get the collection item index
      item = (long) SendMessage(hwndListBox, LB__getITEMDATA, index, 0);
   
      // select the item
#ifdef _DEBUG
      {
         IltmmRenderer* pRenderer;
         IltmmRenderers_Item(pRenderers, item, &pRenderer);
         hr = IltmmRenderer__put_Selected(pRenderer, VARIANT_TRUE);
         IUnknown_Release(pRenderer);
      }
#else
      hr = IltmmRenderers__put_Selection(pRenderers, item);
#endif
      // if new selection failed, we need to force the listbox to match the actual selection
      if(FAILED(hr))
      {
         // get the real selection
         IltmmRenderers__get_Selection(pRenderers, &item);   
   
         // find the matching listbox item
         count = (int) SendMessage(hwndListBox, LB__getCOUNT, 0, 0);

         for(i = 0; i < count; i++)
         {
            if(item == (long) SendMessage(hwndListBox, LB__getITEMDATA, i, 0))
            {
               SendMessage(hwndListBox, LB_SETCURSEL, i, 0);
               break;
            }
         }

      }
   
   }

}

//
// RefreshRendererList
// called when to completely rebuild the collection
//
// pRenderers = renderer collection's interface pointer
// hwndListBox = listbox window handle
//
void RefreshRendererList(IltmmRenderers* pRenderers, HWND hwndListBox)
{
   IltmmRenderer* pRenderer;
   long item;
   BSTR bstr;


   // get the currently selected item   
   IltmmRenderers__get_Selection(pRenderers, &item);

   if(item >= 0)
   {
      // get it's unique name
      IltmmRenderers_Item(pRenderers, item, &pRenderer);
      IltmmRenderer__get_Name(pRenderer, &bstr);
      IUnknown_Release(pRenderer);
   }
   else
   {
      bstr = NULL;
   }

   // rebuild the collection
   IltmmRenderers_Refresh(pRenderers);
   
   if(bstr)
   {
      // find the previously selected item
      IltmmRenderers_Find(pRenderers, bstr, &item);

      // make it the current selection
      if(item >= 0)
         IltmmRenderers__put_Selection(pRenderers, item);      
         
      SysFreeString(bstr);
   }

   // rebuild the listbox
   BuildRendererList(pRenderers, hwndListBox);
}

//
// RendererDlgProc
// selects object renderers
//
BOOL CALLBACK RendererDlgProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
   IltmmRenderers* pRenderers;
   
   switch (msg) 
   {
   case WM_INITDIALOG:
      // initialize the audio renderer listbox
      IltmmPlay__get_AudioRenderers(g_pPlay, &pRenderers);
      BuildRendererList(pRenderers, GetDlgItem(hwnd, IDC_AUDIODEVICES));
      IUnknown_Release(pRenderers);

      
      return TRUE;
      break;

   case WM_COMMAND:
      switch(LOWORD(wParam))
      {
      case IDC_REFRESHAUDIODEVICES:
         // refresh the audio renderer listbox
         IltmmPlay__get_AudioRenderers(g_pPlay, &pRenderers);
         RefreshRendererList(pRenderers, GetDlgItem(hwnd, IDC_AUDIODEVICES));
         IUnknown_Release(pRenderers);
         return TRUE;
         break;
      case IDC_AUDIODEVICES:
         if(HIWORD(wParam) == LBN_SELCHANGE)
         {
            // select the audio renderer
            IltmmPlay__get_AudioRenderers(g_pPlay, &pRenderers);
            RendererSelectionChanged(pRenderers, GetDlgItem(hwnd, IDC_AUDIODEVICES));
            IUnknown_Release(pRenderers);
         }
         break;
         
      case IDOK:
         EndDialog(hwnd, IDOK);
         return TRUE;
         break;
      }
      break;
   }
   return FALSE;
   
}

   
int APIENTRY WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow)
{
   HRESULT hr;
   
   g_hInstance = hInstance;

   // initialize COM library
   hr = CoInitialize(NULL);
   if(FAILED(hr))
      goto error;
   
   // create the play object
   hr = CoCreateInstance(&CLSID_ltmmPlay, NULL, CLSCTX_INPROC_SERVER, &IID_IltmmPlay, (void**) &g_pPlay);
   if(FAILED(hr))
      goto error;
   
   
   DialogBox(g_hInstance, (LPCTSTR)IDD_DEVICEDLG, NULL, RendererDlgProc);


error:
   // cleanup

   if(g_pPlay)
      IUnknown_Release(g_pPlay);

   CoUninitialize();
   
   return 0;
}