Selecting ltmmCapture Object Target Devices for C++

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

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

HINSTANCE g_hInstance; // application instance handle
IltmmCapture* g_pCapture; // capture object's interface pointer

//
// BuildTargetDeviceList
// fills a listbox to match the contents of the collection
//
// pTargetDevices = device collection's interface pointer
// hwndListBox = listbox window handle
//
void BuildTargetDeviceList(IltmmTargetDevices* pTargetDevices, 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
   pTargetDevices->get_Count (&count);

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

      // retrieve collection item
      pTargetDevices->Item (i, &pTargetDevice);
   
      // get displayable name
      pTargetDevice->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
      pTargetDevice->get_Selected (&f);
      if(f)
         selected = i;
   
      // free the collection item
      pTargetDevice->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;
      }
   }

}

//
// TargetDeviceSelectionChanged
// called to reflect changes in the listbox selection//
// pTargetDevices = device collection's interface pointer
// hwndListBox = listbox window handle
//
void TargetDeviceSelectionChanged(IltmmTargetDevices* pTargetDevices, 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
      pTargetDevices->put_Selection (-1);
   }
   else
   {

      // get the collection item index
      item = (long) SendMessage(hwndListBox, LB__getITEMDATA, index, 0);
   
      // select the item
#ifdef _DEBUG
      {
         IltmmTargetDevice* pTargetDevice;
         pTargetDevices->Item (item, &pTargetDevice);
         hr = pTargetDevice->put_Selected (VARIANT_TRUE);
         pTargetDevice->Release ();
      }
#else
      hr = pTargetDevices->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
         pTargetDevices->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;
            }
         }

      }
   
   }

}

//
// RefreshTargetDeviceList
// called when to completely rebuild the collection
//
// pTargetDevices = device collection's interface pointer
// hwndListBox = listbox window handle
//
void RefreshTargetDeviceList(IltmmTargetDevices* pTargetDevices, HWND hwndListBox)
{
   IltmmTargetDevice* pTargetDevice;
   long item;
   BSTR bstr;


   // get the currently selected item   
   pTargetDevices->get_Selection (&item);

   if(item >= 0)
   {
      // get it's unique name
      pTargetDevices->Item (item, &pTargetDevice);
      pTargetDevice->get_Name (&bstr);
      pTargetDevice->Release ();
   }
   else
   {
      bstr = NULL;
   }

   // rebuild the collection
   pTargetDevices->Refresh ();
   
   if(bstr)
   {
      // find the previously selected item
      pTargetDevices->Find (bstr, &item);

      // make it the current selection
      if(item >= 0)
         pTargetDevices->put_Selection (item);      
         
      SysFreeString(bstr);
   }

   // rebuild the listbox
   BuildTargetDeviceList(pTargetDevices, hwndListBox);
}

//
// TargetDeviceDlgProc
// selects object devices
//
BOOL CALLBACK TargetDeviceDlgProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
   IltmmTargetDevices* pTargetDevices;
   
   switch (msg) 
   {
   case WM_INITDIALOG:
      // initialize the target device listbox
      g_pCapture->get_TargetDevices (&pTargetDevices);
      BuildTargetDeviceList(pTargetDevices, GetDlgItem(hwnd, IDC_TARGETDEVICES));
      pTargetDevices->Release ();
      
      return TRUE;
      break;

   case WM_COMMAND:
      switch(LOWORD(wParam))
      {
      case IDC_REFRESHTARGETDEVICES:
         // initialize the target device listbox
         g_pCapture->get_TargetDevices (&pTargetDevices);
         RefreshTargetDeviceList(pTargetDevices, GetDlgItem(hwnd, IDC_TARGETDEVICES));
         pTargetDevices->Release ();
         return TRUE;
         break;

      case IDC_TARGETDEVICES:
         if(HIWORD(wParam) == LBN_SELCHANGE)
         {
            // select the target device
            g_pCapture->get_TargetDevices (&pTargetDevices);
            TargetDeviceSelectionChanged(pTargetDevices, GetDlgItem(hwnd, IDC_TARGETDEVICES));
            pTargetDevices->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_TARGETDEVICEDLG, NULL, TargetDeviceDlgProc);


error:
   // cleanup

   if(g_pCapture)
      g_pCapture->Release ();

   CoUninitialize();
   
   return 0;
}