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 
#ifndef COBJMACROS 
   #define COBJMACROS 
#endif 
 
#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; 
 
   lParam = lParam ; 
 
   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; 
 
} 
 
void SelectingltmmPlayObjectRenderers_Example ( HINSTANCE hInstance /*application instance handle*/ ) 
{ 
   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(); 
} 

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