Using ActiveX controls in GUI application, which uses TestStand API

Question

When using ActiveX controls in TestStand Operator Interface GUI,
CVI reports User Interface Library error no.-143:
"ActiveX control Error" on attempt to load panel, which contains ActiveX controls.
The same code, which takes care of user interface, but not references
TestStand ActiveX API (i.e. not creates TS Engine), works properly.
What's wrong?

Answer 1

Hello again Misha,
Sorry about my previous answer, I overlooked the fact that you were saying this error was caused by placing ActiveX controls in your Operator Interface (OI) GUI (as my example shows I thought the problem was with GUIs displayed from step code modules).
Nevertheless, the problem is still being caused by the same issue, and is solved in a similar fashion. The source for the CVI OI initializes the TestStand engine before it loads/displays the UI panels. The calls to initialize the engine seem to be CoInitializing the main GUI thread as multithreaded apartment (MTA) mode whereas you will need it to be single threaded apartment (STA) mode in order for the ActiveX control container to work properly. The TestStand engine is compatible with either modes, but only one can be in place at a given time. If we CoInitialize the OI's main GUI thread as STA this will solve the problem (the subsequent attempts of setting it to MTA will fail, but again this is ok since the engine is compatible with STA).
In order to perform this functionality you will need to put a call to CoInitializeEx in the main function of the CVI OI source (this will also require that you #include the "windows.h" file at the top of the source also). Here is what the main function in your main.c file for the CVI OI will look like once you have done this:
int main(int argc, char **argv)
int retval = -1;
sArgc = argc;
sArgv = argv;
if(InitCVIRTE(0, argv, 0) == 0) /* Initialize CVI libraries */
goto Done; /* out of memory */
// Intialize main GUI thread as STA to prevent other attempt to make it
// MTA, which will not allow ActiveX controls to be used.
CoInitializeEx(NULL, COINIT_APARTMENTTHREADED);
/* initialize the test engine */
if(!InitEngine())
goto Done;
if(!InitErrorDialogStrings())
goto Done;
if(!InStandaloneExecutable() && !DisplayRunningInEnvironmentWarning())
goto Done; // get out now
if(!ProcessPreLoginCmdlineArgs())
goto Done;
if(!CfgFile_Load())
goto Done;
if(!CfgFile_RestoreOptionSettings())
goto Done;
if(LoadGUIPanels() < 0)
goto Done;
if(!InitFileQuickList())
goto Done;
/* set initial gui state */
if(!InitGUI())
goto Done;
RunUserInterface();
retval = 0; /* normal exist status */
Done:
/* cleanup */
SeqFileList_DeleteAllSequenceFileRecords();
ExeList_DeleteAllRecords();
IconList_DeleteIconList();
SaveAndCleanupFileQuickList();
CfgFile_SaveOptionSettings();
CfgFile_WriteAndCleanupForExit();
AdaptList_DeleteAdapterList();
DestroyToolMenus();
CloseEngine();
FreeErrorDialogStrings();
return retval;
Note: Remember to #include "windows.h" at the very top of the main.c file and to include ole32.lib in your project file list in order to link in the definition for CoInitializeEx.
Jason F.
Applications Engineer
National Instruments
www.ni.com/ask