C++ callback to C#
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  1. #1
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    C++ callback to C#

    Hi all,


    I need to create a C++ callback call in C#.

    Following the third part SDK documentation:


    DVR_GetCameraInfo(HSERVER hServer, LPST_CAMERA_INFO lpstCameraInfo);

    ST_CAMERA_INFO
    This data type contains information relevant to a camera.

    typedef struct _tagCameraInfo
    {
    LPVOIDlpfnCameraCallback;
    }ST_CAMERA_INFO,FAR * LPST_CAMERA_INFO;

    lpfnCameraInfoCallback: The address of the returning a result of a callback.

    DVR_ONCAMERACALLBACK
    A callback function that is called automatically when a client request camera information.

    VOID DVR_OnCameraCallback(HSERVER hServer, LPST_EACH_CAMERA_INFO lpstEachCameraInfo);

    hServer: (out) A connected server handle.
    lpstEachCameraInfo: (out) Information regarding a specific camera. Please refer to ST_EACH_CAMERA_INFO in the 'Data Types' section for more details.

    ST_EACH_CAMERA_INFO
    This data type contains information relevant to a camera.

    typedef struct _tagEachCameraInfo
    {
    CHAR szCamName[32];
    WORD wWidth;
    WORD wHeight;
    BYTE byFramerate;
    BYTE bySchedule;
    BYTE byQuality;
    BYTE byAudio;
    BYTE byVideoStandard;
    BYTE byCovert;
    BYTE byPTZ;
    BYTE byVideoLoss;
    INT nAlarmIn;
    INT nAlarmOut;
    }ST_EACH_CAMERA_INFO,FAR *LPST_EACH_CAMERA_INFO;

    Following my C# wrapper:

    Code:
    public static class SDKInterop
    {
    
    [StructLayout(LayoutKind.Sequential)] public struct ST_CAMERA_INFO {
    public DVR_OnCameraCallback lpfnCameraCallback;
    } [StructLayout(LayoutKind.Sequential)] public struct ST_EACH_CAMERA_INFO {
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)] public char[] szCamName; public ushort wWidth; public ushort wHeight; public byte byFramerate; public byte bySchedule; public byte byQuality; public byte byAudio; public byte byVideoStandard; public byte byCovert; public byte byPTZ; public byte byVideoLoss; public int nAlarmIn; public int nAlarmOut;
    } [UnmanagedFunctionPointer(CallingConvention.Cdecl)] public delegate void DVR_OnCameraCallback(out UIntPtr hServer, out ST_EACH_CAMERA_INFO lpstEachCameraInfo); [DllImport(NETWORKCLIENT_DLL_LOCATION, CallingConvention = CallingConvention.Cdecl)] public static extern Int32 DVR_GetCameraInfo(UIntPtr hServer, ref ST_CAMERA_INFO lpstCameraInfo);
    }

    Following the function calls:

    Code:
    SDKInterop.ST_CAMERA_INFO _cameraInfo;
    
    _cameraInfo.lpfnCameraCallback = (hS, cI) =>
    {
    
    // some code
    }; int success = SDKInterop.DVR_GetCameraInfo(_hServer, ref _cameraInfo);

    Unfortunately it doesn't work because an error message from _cameraInfo.lpfnCameraCallback tells: "Parameter 1 must be declared with the 'out' keyword".

    Please could you help me?

    Thank you,

    Marco

  2. #2
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    Re: C++ callback to C#

    change 'out' to 'ref'. Output parameters are not passed by reference.

    Hope this helps
    Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning. - Rich Cook


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  3. #3
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    Re: C++ callback to C#

    Quote Originally Posted by HairyMonkeyMan View Post
    change 'out' to 'ref'. Output parameters are not passed by reference.

    Hope this helps

    Do you mean something like this?

    Code:
    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    public delegate void DVR_OnCameraCallback(ref UIntPtr hServer, ref ST_EACH_CAMERA_INFO lpstEachCameraInfo);

    Visual Studio returns error on:

    Code:
    _cameraInfo.lpfnCameraCallback = (hS, cI) =>
    {
    
    // some code
    };

  4. #4
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    Re: C++ callback to C#

    can you upload a repro in a zip?
    Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning. - Rich Cook


    0100 1101 0110 1001 0110 0011 0110 1000 0110 0001 0110 0101 0110 1100 0010 0000 0100 0101 0110 1100 0110 1100 0110 0101 0111 0010

  5. #5
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    Re: C++ callback to C#

    did you try changing the definition of...

    Code:
    public static extern Int32 DVR_GetCameraInfo(UIntPtr hServer, ref ST_CAMERA_INFO lpstCameraInfo);
    to

    Code:
    public static extern Int32 DVR_GetCameraInfo(out UIntPtr hServer, out ST_CAMERA_INFO lpstCameraInfo);

  6. #6
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    Re: C++ callback to C#

    Quote Originally Posted by sotoasty View Post
    did you try changing the definition of...

    Code:
    public static extern Int32 DVR_GetCameraInfo(UIntPtr hServer, ref ST_CAMERA_INFO lpstCameraInfo);
    to

    Code:
    public static extern Int32 DVR_GetCameraInfo(out UIntPtr hServer, out ST_CAMERA_INFO lpstCameraInfo);

    Yes I've tried also with your code but I don't know how to call:

    Code:
    _cameraInfo.lpfnCameraCallback = (hS, cI) =>
    {
    // some code
    };

    @HairyMonkeyMan

    Following a repro zip (rename to .zip):

    ConsoleApplication1.doc


    Thanks

  7. #7
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    Re: C++ callback to C#

    Hi Marco,

    I changed the DVR_OnCameraCallback delegate in Interop.cs as follows;

    Code:
    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    public delegate void DVR_OnCameraCallback(UIntPtr hServer, ST_EACH_CAMERA_INFO lpstEachCameraInfo);
    If I put a breakpoint inside the callback on Server.cs I can see it being hit.

    Does this solve it?
    Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning. - Rich Cook


    0100 1101 0110 1001 0110 0011 0110 1000 0110 0001 0110 0101 0110 1100 0010 0000 0100 0101 0110 1100 0110 1100 0110 0101 0111 0010

  8. #8
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    Re: C++ callback to C#

    Quote Originally Posted by HairyMonkeyMan View Post
    Hi Marco,

    I changed the DVR_OnCameraCallback delegate in Interop.cs as follows;

    Code:
    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    public delegate void DVR_OnCameraCallback(UIntPtr hServer, ST_EACH_CAMERA_INFO lpstEachCameraInfo);
    If I put a breakpoint inside the callback on Server.cs I can see it being hit.

    Does this solve it?

    Great HairyMonkeyMan,


    the callback is working!


    If I watch into cI object, I see that the values are wrong but the struct ST_EACH_CAMERA_INFO in the Interop class seems to be correct.


    I receive something like this:


    Name:  struct_result.png
Views: 83
Size:  7.1 KB


    What do you think?


    Thanks

    Marco

  9. #9
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    Re: C++ callback to C#

    try defining your struct as follows:

    Code:
            [StructLayout(LayoutKind.Sequential)]
            public struct ST_EACH_CAMERA_INFO
            {
                [MarshalAs(UnmanagedType.LPStr)]
                public string szCamName;
                public ushort wWidth;
                public ushort wHeight;
                public Byte byFramerate;
                public Byte bySchedule;
                public Byte byQuality;
                public Byte byAudio;
                public Byte byVideoStandard;
                public Byte byCovert;
                public Byte byPTZ;
                public Byte byVideoLoss;
                public IntPtr nAlarmIn;
                public IntPtr nAlarmOut;
            }
    Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning. - Rich Cook


    0100 1101 0110 1001 0110 0011 0110 1000 0110 0001 0110 0101 0110 1100 0010 0000 0100 0101 0110 1100 0110 1100 0110 0101 0111 0010

  10. #10
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    Re: C++ callback to C#

    Quote Originally Posted by HairyMonkeyMan View Post
    try defining your struct as follows:

    Code:
            [StructLayout(LayoutKind.Sequential)]
            public struct ST_EACH_CAMERA_INFO
            {
                [MarshalAs(UnmanagedType.LPStr)]
                public string szCamName;
                public ushort wWidth;
                public ushort wHeight;
                public Byte byFramerate;
                public Byte bySchedule;
                public Byte byQuality;
                public Byte byAudio;
                public Byte byVideoStandard;
                public Byte byCovert;
                public Byte byPTZ;
                public Byte byVideoLoss;
                public IntPtr nAlarmIn;
                public IntPtr nAlarmOut;
            }

    The szCamName now is right.

    But the other values are wrongs again.


    The documentation is the following:

    ST_EACH_CAMERA_INFO
    This data type contains information relevant to a camera.

    typedef struct _tagEachCameraInfo
    {
    CHAR szCamName[32];
    WORD wWidth;
    WORD wHeight;
    BYTE byFramerate;
    BYTE bySchedule;
    BYTE byQuality;
    BYTE byAudio;
    BYTE byVideoStandard;
    BYTE byCovert;
    BYTE byPTZ;
    BYTE byVideoLoss;
    INT nAlarmIn;
    INT nAlarmOut;
    }ST_EACH_CAMERA_INFO,FAR *LPST_EACH_CAMERA_INFO;

    szCamName: The camera's name.
    wWidth: The width of camera's video.
    wHeight: The height of camera's video.
    byFramerate: The speed of the camera's video.
    bySchedule: The camera's video schedule, specifically when the camera will begin recording video. The following are valid values:
    0 for No Recording
    1 for Normal
    2 for Motion
    3 for Alarm Input
    4 for Event
    5 for Data
    byQuality: The camera's video's image quality.
    0 for Lowest
    1 for Low
    2 for Normal
    3 for High
    4 for Best
    byAudio: The camera's audio mapping.
    0 for No Use
    1 - 8 for a specific audio channel
    byVideoStandard: The tv video standard/format being used.
    0 for NTSC
    1 for PAL
    byCovert: video coversion??
    0 for disabled
    1 for enabled
    byPTZ: pan, tilt, zoom
    0 for disabled
    1 for enabled
    byVideoLoss: video loss detection
    0 for disabled
    1 for enabled
    nAlarmIn: The number of alarm inputs.
    nAlarmOut: The number of alarm outputs.


  11. #11
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    Re: C++ callback to C#

    I'll not be online for a while, but have a look at the following (its not complete, but should be able to help)

    http://msdn.microsoft.com/en-us/libr...(v=vs.90).aspx
    Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning. - Rich Cook


    0100 1101 0110 1001 0110 0011 0110 1000 0110 0001 0110 0101 0110 1100 0010 0000 0100 0101 0110 1100 0110 1100 0110 0101 0111 0010

  12. #12
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    Re: C++ callback to C#

    Quote Originally Posted by HairyMonkeyMan View Post
    I'll not be online for a while, but have a look at the following (its not complete, but should be able to help)

    http://msdn.microsoft.com/en-us/libr...(v=vs.90).aspx
    Thanks a lot...it helps me!



    I've another question about this callback.


    I discovered from documentation that the second param of the DVR_OnCameraCallback must be an array of ST_EACH_CAMERA_INFO:

    Code:
    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    public delegate void DVR_OnCameraCallback(UIntPtr hServer, ST_EACH_CAMERA_INFO lpstEachCameraInfo);

    How can I modify the above delegate in order to let it works correctly?


    I think that there are 2 solutions: one is to passing directly an array of ST_EACH_CAMERA_INFO to the delegate, otherwise the second is to passing an IntPtr and then convert it into a ST_EACH_CAMERA_INFO array.


    Please could someone suggest me the right way to let a callback returns an array of struct?


    Thanks!

    Marco

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