Selecting ltmmCapture Object Devices for C

The following example shows how to enumerate and select ltmmCapture object devices.

// 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
IltmmCapture* g_pCapture;      // convert object's interface pointer

//
// BuildDeviceList
// fills a listbox to match the contents of the collection
//
// pDevices = device collection's interface pointer
// hwndListBox = listbox window handle
//
void BuildDeviceList(IltmmDevices* pDevices, 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
   IltmmDevices_get_Count(pDevices, &count); 

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

      // retrieve collection item
      IltmmDevices_Item(pDevices, i, &pDevice); 
   
      // get displayable name
      IltmmDevice_get_FriendlyName(pDevice, &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
      IltmmDevice_get_Selected(pDevice, &f); 
      if(f) 
         selected = i; 
   
      // free the collection item
      IUnknown_Release(pDevice); 
   }

   // 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; 
      }
   }

}

//
// DeviceSelectionChanged
// called to reflect changes in the listbox selection
//
// pDevices = device collection's interface pointer
// hwndListBox = listbox window handle
//
void DeviceSelectionChanged(IltmmDevices* pDevices, 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
      IltmmDevices_put_Selection(pDevices, -1); 
   }
   else
   {

      // get the collection item index
      item = (long) SendMessage(hwndListBox, LB__getITEMDATA, index, 0); 
   
      // select the item
#ifdef _DEBUG
      {
         IltmmDevice* pDevice; 
         IltmmDevices_Item(pDevices, item, &pDevice); 
         hr = IltmmDevice_put_Selected(pDevice, VARIANT_TRUE); 
         IUnknown_Release(pDevice); 
      }
#else
      hr = IltmmDevices_put_Selection(pDevices, item); 
#endif
      // if new selection failed, we need to force the listbox to match the actual selection
      if(FAILED(hr)) 
      {
         // get the real selection
         IltmmDevices_get_Selection(pDevices, &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; 
            }
         }

      }
   
   }

}

//
// RefreshDeviceList
// called when to completely rebuild the collection
//
// pDevices = device collection's interface pointer
// hwndListBox = listbox window handle
//
void RefreshDeviceList(IltmmDevices* pDevices, HWND hwndListBox) 
{
   IltmmDevice* pDevice; 
   long item; 
   BSTR bstr; 


   // get the currently selected item   
   IltmmDevices_get_Selection(pDevices, &item); 

   if(item >= 0) 
   {
      // get it's unique name
      IltmmDevices_Item(pDevices, item, &pDevice); 
      IltmmDevice_get_Name(pDevice, &bstr); 
      IUnknown_Release(pDevice); 
   }
   else
   {
      bstr = NULL; 
   }

   // rebuild the collection
   IltmmDevices_Refresh(pDevices); 
   
   if(bstr) 
   {
      // find the previously selected item
      IltmmDevices_Find (pDevices, bstr, &item); 

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

   // rebuild the listbox
   BuildDeviceList(pDevices, hwndListBox); 
}

//
// DeviceDlgProc
// selects object devices
//
BOOL CALLBACK DeviceDlgProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) 
{
   IltmmDevices* pDevices; 
   
   switch (msg) 
   {
   case WM_INITDIALOG: 
      // initialize the audio device listbox
      IltmmCapture_get_AudioDevices(g_pCapture, &pDevices); 
      BuildDeviceList(pDevices, GetDlgItem(hwnd, IDC_AUDIODEVICES)); 
      IUnknown_Release(pDevices); 

      // initialize the video device listbox
      IltmmCapture_get_VideoDevices(g_pCapture, &pDevices); 
      BuildDeviceList(pDevices, GetDlgItem(hwnd, IDC_VIDEODEVICES)); 
      IUnknown_Release(pDevices); 
      
      return TRUE; 
      break; 

   case WM_COMMAND: 
      switch(LOWORD(wParam)) 
      {
      case IDC_REFRESHAUDIODEVICES: 
         // refresh the audio device listbox
         IltmmCapture_get_AudioDevices(g_pCapture, &pDevices); 
         RefreshDeviceList(pDevices, GetDlgItem(hwnd, IDC_AUDIODEVICES)); 
         IUnknown_Release(pDevices); 
         return TRUE; 
         break; 
      case IDC_AUDIODEVICES: 
         if(HIWORD(wParam) == LBN_SELCHANGE) 
         {
            // select the audio device
            IltmmCapture_get_AudioDevices(g_pCapture, &pDevices); 
            DeviceSelectionChanged(pDevices, GetDlgItem(hwnd, IDC_AUDIODEVICES)); 
            IUnknown_Release(pDevices); 
         }
         break; 
         
      case IDC_REFRESHVIDEODEVICES: 
         // initialize the video device listbox
         IltmmCapture_get_VideoDevices(g_pCapture, &pDevices); 
         RefreshDeviceList(pDevices, GetDlgItem(hwnd, IDC_VIDEODEVICES)); 
         IUnknown_Release(pDevices); 
         return TRUE; 
         break; 

      case IDC_VIDEODEVICES: 
         if(HIWORD(wParam) == LBN_SELCHANGE) 
         {
            // select the video device
            IltmmCapture_get_VideoDevices(g_pCapture, &pDevices); 
            DeviceSelectionChanged(pDevices, GetDlgItem(hwnd, IDC_VIDEODEVICES)); 
            IUnknown_Release(pDevices); 
         }
         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 convert object
   hr = CoCreateInstance(&CLSID_ltmmCapture, NULL, CLSCTX_INPROC_SERVER, &IID_IltmmCapture, (void**) &g_pCapture); 
   if(FAILED(hr)) 
      goto error; 
   
   
   DialogBox(g_hInstance, (LPCTSTR)IDD_DEVICEDLG, NULL, DeviceDlgProc); 


error: 
   // cleanup

   if(g_pCapture) 
      IUnknown_Release(g_pCapture); 

   CoUninitialize();
   
   return 0; 
}