RE: Callback not being called

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Hi Peter,

Thanks for the help you are providing me.

Were you able to get this code to work in an application? My unmanaged C++
code is targeted as a Smart Device DLL. My application is a smart device
application. I took the modifications you suggested and placed into mine.
The callback in the unmanaged code appears to fire, but the managed code
never receives it. I appreciate any help you can provide.



""Peter Huang" [MSFT]" wrote:

Hi,

Based on my research, you need to change two place.
1. change the CallingConvention of the C++ export function.

typedef void (__stdcall *callBackTypeReturningStrings)(LPTSTR*
ppStringArray, int cArray);

callBackTypeReturningStrings gTheCallBackReturningStrings;
unsigned int timerHandle;

void CALLBACK TimerProc(
HWND hwnd,
UINT uMsg,
UINT idEvent,
DWORD dwTime )
{
LPTSTR ppStringArray[2];

ppStringArray[0]=SysAllocString(L"string 1");
ppStringArray[1]=SysAllocString(L"string 2");

gTheCallBackReturningStrings(ppStringArray,2);
SysFreeString(ppStringArray[0]);
SysFreeString(ppStringArray[1]);
KillTimer(NULL,timerHandle);
}

extern "C" CPPDLLFUNCTIONPOINTER_API void
InitCallBackReturningStringFromTimer(callBackTypeReturningStrings
theCallBack,LPTSTR* ppStringArray, int cArray)
{
gTheCallBackReturningStrings = theCallBack;
timerHandle = SetTimer(NULL,NULL,5000,TimerProc);
}

2. Change the .NET call back function signature, we need to tell the .NET
runtime, how many items we need to marshalling. And we need to use
PtrToStringBSTR, because the SysAllocString will return a BSTR.

[DllImport(DLLPATH, CallingConvention = CallingConvention.StdCall)]
private static extern void
InitCallBackReturningStringFromTimer(CallBackDelegateReturningStringFromTime
r theCallBack, IntPtr[] ppStringArray, int nCount);
delegate void CallBackDelegateReturningStringFromTimer([In,Out,
MarshalAs(UnmanagedType.LPArray,SizeParamIndex=1)] IntPtr[] theStrings, int
nCount);
public void CallBackMethodStringFromTimer([In,Out,
MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)] IntPtr[]
ppStringArray, int nCount)
{
String myString;
myString = Marshal.PtrToStringBSTR(ppStringArray[0]);
Console.WriteLine(myString);
myString = Marshal.PtrToStringBSTR(ppStringArray[1]);
Console.WriteLine(myString);
Console.WriteLine("In Callback from timer");
}

Best regards,

Peter Huang

Microsoft Online Community Support
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