Selecting ltmmCapture Object Devices for C++

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

#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 
   pDevices->get_Count (&count);  
 
   for(i = 0; i < count; i++) 
   { 
      IltmmDevice* pDevice;  
      BSTR bstr;  
      TCHAR sz[256];  
      int index;  
      VARIANT_BOOL f;  
 
      // retrieve collection item 
      pDevices->Item (i, &pDevice);  
    
      // get displayable name 
      pDevice->get_FriendlyName (&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 
      pDevice->get_Selected (&f);  
      if (f)  
         selected = i;  
    
      // free the collection item 
      pDevice->Release(); 
   } 
 
   // 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 
      pDevices->put_Selection (-1);  
   } 
   else 
   { 
      // get the collection item index 
      item = (long) SendMessage(hwndListBox, LB_GETITEMDATA, index, 0);  
    
      // select the item 
#ifdef _DEBUG 
      { 
         IltmmDevice* pDevice;  
         pDevices->Item (item, &pDevice);  
         hr = pDevice->put_Selected(VARIANT_TRUE);  
         pDevice->Release(); 
      } 
#else 
      hr = pDevices->put_Selection (item);  
#endif 
      // if new selection failed, we need to force the listbox to match the actual selection 
      if (FAILED(hr))  
      { 
         // get the real selection 
         pDevices->get_Selection (&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    
   pDevices->get_Selection (&item);  
 
   if (item >= 0)  
   { 
      // get it's unique name 
      pDevices->Item (item, &pDevice);  
      pDevice->get_Name (&bstr);  
      pDevice->Release(); 
   } 
   else 
   { 
      bstr = NULL;  
   } 
 
   // rebuild the collection 
   pDevices->Refresh (); 
    
   if (bstr)  
   { 
      // find the previously selected item 
      pDevices->Find(bstr, &item);  
 
      // make it the current selection 
      if (item >= 0)  
         pDevices->put_Selection (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 
      g_pCapture->get_AudioDevices (&pDevices);  
      BuildDeviceList(pDevices, GetDlgItem(hwnd, IDC_AUDIODEVICES));  
      pDevices->Release(); 
 
      // initialize the video device listbox 
      g_pCapture->get_VideoDevices (&pDevices);  
      BuildDeviceList(pDevices, GetDlgItem(hwnd, IDC_VIDEODEVICES));  
      pDevices->Release(); 
       
      return TRUE;  
      break;  
 
   case WM_COMMAND:  
      switch(LOWORD(wParam))  
      { 
      case IDC_REFRESHAUDIODEVICES:  
         // refresh the audio device listbox 
         g_pCapture->get_AudioDevices (&pDevices);  
         RefreshDeviceList(pDevices, GetDlgItem(hwnd, IDC_AUDIODEVICES));  
         pDevices->Release(); 
         return TRUE;  
         break;  
      case IDC_AUDIODEVICES:  
         if (HIWORD(wParam) == LBN_SELCHANGE)  
         { 
            // select the audio device 
            g_pCapture->get_AudioDevices (&pDevices);  
            DeviceSelectionChanged(pDevices, GetDlgItem(hwnd, IDC_AUDIODEVICES));  
            pDevices->Release(); 
         } 
         break;  
          
      case IDC_REFRESHVIDEODEVICES:  
         // initialize the video device listbox 
         g_pCapture->get_VideoDevices (&pDevices);  
         RefreshDeviceList(pDevices, GetDlgItem(hwnd, IDC_VIDEODEVICES));  
         pDevices->Release(); 
         return TRUE;  
         break;  
 
      case IDC_VIDEODEVICES:  
         if (HIWORD(wParam) == LBN_SELCHANGE)  
         { 
            // select the video device 
            g_pCapture->get_VideoDevices (&pDevices);  
            DeviceSelectionChanged(pDevices, GetDlgItem(hwnd, IDC_VIDEODEVICES));  
            pDevices->Release(); 
         } 
         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)  
      g_pCapture->Release(); 
 
   CoUninitialize(); 
    
   return 0;  
} 

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