Selecting ltmmCapture Object Inputs for C

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

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

//
// BuildCaptureInputList
// fills a listbox to match the contents of the collection
//
// pCaptureInputs = input collection's interface pointer
// hwndListBox = listbox window handle
//
void BuildCaptureInputList(IltmmCaptureInputs* pCaptureInputs, 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
   IltmmCaptureInputs_get_Count (pCaptureInputs, &count); 

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

      // retrieve collection item
      IltmmCaptureInputs_Item (pCaptureInputs, i, &pCaptureInput); 

      // get displayable name
      IltmmCaptureInput_get_Name (pCaptureInput, &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
      IltmmCaptureInput_get_Selected (pCaptureInput, &f); 
      if(f) 
         selected = i; 

      // free the collection item
      IUnknown_Release(pCaptureInput); 
   }

   // 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; 
      }
   }

}

//
// CaptureInputSelectionChanged
// called to reflect changes in the listbox selection
//
// pCaptureInputs = input collection's interface pointer
// hwndListBox = listbox window handle
//
void CaptureInputSelectionChanged(IltmmCaptureInputs* pCaptureInputs, 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
      IltmmCaptureInputs_put_Selection (pCaptureInputs, -1); 
   }
   else
   {

      // get the collection item index
      item = (long) SendMessage(hwndListBox, LB_GETITEMDATA, index, 0); 

      // select the item
#ifdef _DEBUG
      {
         IltmmCaptureInput* pCaptureInput; 
         IltmmCaptureInputs_Item (pCaptureInputs, item, &pCaptureInput); 
         hr = IltmmCaptureInput_put_Selected (pCaptureInput, VARIANT_TRUE); 
         IUnknown_Release(pCaptureInput); 
      }
#else
      hr = IltmmCaptureInputs_put_Selection (pCaptureInputs, item); 
#endif
      // if new selection failed, we need to force the listbox to match the actual selection
      if(FAILED(hr)) 
      {
         // get the real selection
         IltmmCaptureInputs_get_Selection (pCaptureInputs, &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; 
            }
         }

      }

   }

}

//
// SelectCompositeVideo
// selects composite video, if available
//
// pCaptureInputs = input collection's interface pointer
// hwndListBox = listbox window handle
//
void SelectCompositeVideo(IltmmCaptureInputs* pCaptureInputs, HWND hwndListBox) 
{
   long item; 
   BSTR bstr; 
   long i; 
   long count; 

   // Find the composite video input
   bstr = SysAllocString(L"Video Composite");
   IltmmCaptureInputs_Find(pCaptureInputs, bstr, &item); 
   SysFreeString(bstr); 

   // make it the current selection
   if(item >= 0) 
   {
      IltmmCaptureInputs_put_Selection (pCaptureInputs, item);      

      IltmmCaptureInputs_get_Count (pCaptureInputs, &count); 

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

//
// CaptureInputDlgProc
// selects object inputs
//
BOOL CALLBACK CaptureInputDlgProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) 
{
   IltmmCaptureInputs* pCaptureInputs; 


   wParam = wParam ;
   lParam = lParam ;

   switch (msg) 
   {
   case WM_INITDIALOG: 
      // initialize the video input listbox
      IltmmCapture_get_VideoInputs (g_pCapture, &pCaptureInputs); 
      BuildCaptureInputList(pCaptureInputs, GetDlgItem(hwnd, IDC_VIDEOINPUTS)); 
      IUnknown_Release(pCaptureInputs); 

      return TRUE; 
      break; 

   case WM_COMMAND: 
      switch(LOWORD(wParam)) 
      {
      case IDC_SELECTCOMPOSITEVIDEO: 
         // select composite video
         IltmmCapture_get_VideoInputs (g_pCapture, &pCaptureInputs); 
         SelectCompositeVideo(pCaptureInputs, GetDlgItem(hwnd, IDC_VIDEOINPUTS)); 
         IUnknown_Release(pCaptureInputs); 
         return TRUE; 
         break; 

      case IDC_VIDEOINPUTS: 
         if(HIWORD(wParam) == LBN_SELCHANGE) 
         {
            // select the video input
            IltmmCapture_get_VideoInputs (g_pCapture, &pCaptureInputs); 
            CaptureInputSelectionChanged(pCaptureInputs, GetDlgItem(hwnd, IDC_VIDEOINPUTS)); 
            IUnknown_Release(pCaptureInputs); 
         }
         break; 

      case IDOK: 
         EndDialog(hwnd, IDOK); 
         return TRUE; 
         break; 
      }
      break; 
   }
   return FALSE; 

}


void SelectingltmmCaptureObjectInputs_Example ( HINSTANCE hInstance /*application instance handle*/ )
{
   HRESULT hr; 
   IltmmDevices* pDevices; 

   g_hInstance = hInstance; 

   // initialize COM library
   hr = CoInitialize(NULL); 
   if(FAILED(hr)) 
      goto error; 

   // create the capture object
   hr = CoCreateInstance(&CLSID_ltmmCapture, NULL, CLSCTX_INPROC_SERVER, &IID_IltmmCapture, (void**) &g_pCapture); 
   if(FAILED(hr)) 
      goto error; 

   // select the first audio device available
   IltmmCapture_get_AudioDevices (g_pCapture, &pDevices); 
   IltmmDevices_put_Selection (pDevices, 0); 
   IUnknown_Release(pDevices); 

   // select the first video device available
   IltmmCapture_get_VideoDevices (g_pCapture, &pDevices); 
   IltmmDevices_put_Selection (pDevices, 0); 
   IUnknown_Release(pDevices); 

   DialogBox(g_hInstance, (LPCTSTR)IDD_INPUTDLG, NULL, CaptureInputDlgProc); 


error: 
   // cleanup

   if(g_pCapture) 
      IUnknown_Release(g_pCapture); 

   CoUninitialize();
}