I have developed a MFC ActiveX control, that displays a graph using data retrieved from Kepware OPC Server using OPC Client. OPC Client code is part of ActiveX control code. The OPC client is launched in a separate thread from main control thread. The control works well when there is only one instance of it on the MFC dialog. However if I add another instance of it on same form, the curve on the graph starts malfunctioning. From the logs I can see that Control app class which is ultimately derived from CWinApp is instantiated only once. Any ideas why it is messing up? Are any global variables being shared between two instances? I am using Visual Studio 2008.
1 Answers
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If your ActiveX control is located inside a DLL this DLL is always loaded once into the process that uses the ActiveX control. So it is normal that you only have one CWinApp object even if you have multiple controls.
So you need to design your object in a way, that global data inside the DLL doesn't affect the behaviour or data inside a control instance.
I suppose that you have some global data, that is used by the first control. And when another instance is created this global data is modified by the second instance and the first instance shows wrong data or misbehaves.
All state of such an ActiveX must be located and allocated inside the object.
