Selecting ltmmCapture Object Target Devices for C

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

// 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;      // 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 
   IltmmTargetDevices_get_Count(pTargetDevices, &count);  
 
   for(i = 0; i < count; i++) 
   { 
      IltmmTargetDevice* pTargetDevice;  
      BSTR bstr;  
      TCHAR sz[256];  
      int index;  
      VARIANT_BOOL f;  
 
      // retrieve collection item 
      IltmmTargetDevices_Item(pTargetDevices, i, &pTargetDevice);  
 
      // get displayable name 
      IltmmTargetDevice_get_FriendlyName(pTargetDevice, &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 
      IltmmTargetDevice_get_Selected(pTargetDevice, &f);  
      if(f)  
         selected = i;  
 
      // free the collection item 
      IUnknown_Release(pTargetDevice);  
   } 
 
   // 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 
      IltmmTargetDevices_put_Selection(pTargetDevices, -1);  
   } 
   else 
   { 
 
      // get the collection item index 
      item = (long) SendMessage(hwndListBox, LB_GETITEMDATA, index, 0);  
 
      // select the item 
#ifdef _DEBUG 
      { 
         IltmmTargetDevice* pTargetDevice;  
         IltmmTargetDevices_Item(pTargetDevices, item, &pTargetDevice);  
         hr = IltmmTargetDevice_put_Selected(pTargetDevice, VARIANT_TRUE);  
         IUnknown_Release(pTargetDevice);  
      } 
#else 
      hr = IltmmTargetDevices_put_Selection(pTargetDevices, item);  
#endif 
      // if new selection failed, we need to force the listbox to match the actual selection 
      if(FAILED(hr))  
      { 
         // get the real selection 
         IltmmTargetDevices_get_Selection(pTargetDevices, &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    
   IltmmTargetDevices_get_Selection(pTargetDevices, &item);  
 
   if(item >= 0)  
   { 
      // get it's unique name 
      IltmmTargetDevices_Item(pTargetDevices, item, &pTargetDevice);  
      IltmmTargetDevice_get_Name(pTargetDevice, &bstr);  
      IUnknown_Release(pTargetDevice);  
   } 
   else 
   { 
      bstr = NULL;  
   } 
 
   // rebuild the collection 
 
   IltmmTargetDevices_Refresh(pTargetDevices);  
 
   if(bstr)  
   { 
      // find the previously selected item 
      IltmmTargetDevices_Find(pTargetDevices, bstr, &item);  
 
      // make it the current selection 
      if(item >= 0)  
         IltmmTargetDevices_put_Selection (pTargetDevices, 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;  
 
 
   lParam = lParam ; 
 
   switch (msg)  
   { 
   case WM_INITDIALOG:  
      // initialize the target device listbox 
      IltmmCapture_get_TargetDevices(g_pCapture, &pTargetDevices);  
      BuildTargetDeviceList(pTargetDevices, GetDlgItem(hwnd, IDC_TARGETDEVICES));  
      IUnknown_Release(pTargetDevices);  
 
      return TRUE;  
      break;  
 
   case WM_COMMAND:  
      switch(LOWORD(wParam))  
      { 
      case IDC_REFRESHTARGETDEVICES:  
         // initialize the target device listbox 
         IltmmCapture_get_TargetDevices(g_pCapture, &pTargetDevices);  
         RefreshTargetDeviceList(pTargetDevices, GetDlgItem(hwnd, IDC_TARGETDEVICES));  
         IUnknown_Release(pTargetDevices);  
         return TRUE;  
         break;  
 
      case IDC_TARGETDEVICES:  
         if(HIWORD(wParam) == LBN_SELCHANGE)  
         { 
            // select the target device 
            IltmmCapture_get_TargetDevices(g_pCapture, &pTargetDevices);  
            TargetDeviceSelectionChanged(pTargetDevices, GetDlgItem(hwnd, IDC_TARGETDEVICES));  
            IUnknown_Release(pTargetDevices);  
         } 
         break;  
 
      case IDOK:  
         EndDialog(hwnd, IDOK);  
         return TRUE;  
         break;  
      } 
      break;  
   } 
   return FALSE;  
 
} 
 
void SelectingltmmCaptureObjectTargetDevices_Example ( HINSTANCE hInstance /*application instance handle*/ ) 
{ 
   HRESULT hr;  
 
   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;  
 
 
   DialogBox(g_hInstance, (LPCTSTR)IDD_TARGETDEVICEDLG, NULL, TargetDeviceDlgProc);  
 
 
error:  
   // cleanup 
 
   if(g_pCapture)  
      IUnknown_Release(g_pCapture);  
 
   CoUninitialize(); 
} 

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