Managing C++ Garmin API in C#

[borjolujo]

I want to call Garmin API (http://developer.garmin.com/mobile/mobile-sdk/) in VB.Net Compact Framework project. The API is in C++, so i´m making a C# dll project as intermediate way between API dll and VB.Net. I have some problems while executing my code because it throw a NotSupportedException (bad arguments type, i think) in QueCreatePoint call. Here is the C++ API code, and my C# work:


-- C++ Functions prototype and C# P/Invoke Calls ----------

• QueAPIExport QueErrT16 QueCreatePoint( const QuePointType* point, QuePointHandle* handle );
  
  QueAPIExport QueErrT16 QueClosePoint( QuePointHandle point );
  .
  
• [DllImport("QueAPI.dll")]
  private static extern QueErrT16 QueCreatePoint(ref QuePointType point, ref uint handle);
  
  [DllImport("QueAPI.dll")]
  private static extern QueErrT16 QueRouteToPoint(uint point);

-- QueErrT16 ----------

• typedef uint16 QueErrT16; enum { ... }
  .
• public enum QueErrT16 : ushort { ... }

-- QuePointType ----------

• typedef struct
  {
  char id[25];
  QueSymbolT16 smbl;
  QuePositionDataType posn;
  } QuePointType;
  .
• public struct QuePointType
  {
  public string id;
  public QueSymbolT16 smbl;
  public QuePositionDataType posn;
  }

-- QueSymbolT16 ----------

• typedef uint16 QueSymbolT16; enum { ... }
  .
• public enum QueSymbolT16 : ushort { ... }

-- QuePositionDataType ----------

• typedef struct
  {
  sint32 lat;
  sint32 lon;
  float altMSL;
  } QuePositionDataType;
  .
• public struct QuePositionDataType
  {
  public int lat;
  public int lon;
  public float altMSL;
  }

-- QuePointHandle ----------

• typedef uint32 QuePointHandle;
  .
• In C# i manage it as uint var.

-- And this is my current C# function to call all this ----------

public static QueErrT16 GarminNavigateToCoordinates(double latitude , double longitude)
{
    QueErrT16 err = new QueErrT16();
 
    // Open API
    err = QueAPIOpen();
    if(err != QueErrT16.queErrNone) 
    {
        return err;
    }
 
    // Create position
    QuePositionDataType position = new QuePositionDataType();
    position.lat = GradosDecimalesASemicirculos(latitude);
    position.lon = GradosDecimalesASemicirculos(longitude);
 
    // Create point
    QuePointType point = new QuePointType();
    point.posn = position;
 
    // Crete point handle
    uint hPoint = new uint();
 
    err = QueCreatePoint(ref point, ref hPoint);  // HERE i got a NotSupportedException
    if (err == QueErrT16.queErrNone) 
    {
        err = QueRouteToPoint(hPoint);
    }
 
    // Close API
    QueAPIClose();
 
    return err; 
}

I will appreciate any help. Thanks.

[Plater]

NotSupportedException is generally thrown when you try to use a property/function that is not available in the current implentation.
This could be caused by a number of things.
One of which is using the compact framework, which has limited support or some classes/etc
The other is in inheritance, some derived classes will not use a property/method but the base class has it so it will be listed

[borjolujo]

I think the problem is in the P/Invoke call:

[DllImport("QueAPI.dll")]
private static extern QueErrT16 QueCreatePoint(ref QuePointType point, ref uint handle);

for the C prototype:

QueAPIExport QueErrT16 QueCreatePoint( const QuePointType* point, QuePointHandle* handle );

The parameter are not correct, the API want a pointer and i´m sending var with ref attribute. But when i write this:

[DllImport("QueAPI.dll")]
private static extern QueErrT16 QueCreatePoint(QuePointType* point, uint* handle);

i can´t compile because an error: "Cannot take the address of, get the size of, or declare a pointer to a managed type 'QuePointType'." This is because QuePointType contains a managed type: QuePositionDataType (Pointer types: http://msdn.microsoft.com/en-us/library/y31yhkeb.aspx).

So, i dont know how to send to the function a pointer of my structure.

[Plater]

Your structure is a managed structure then, not pulled from the DLL (if that can even be done)
Have you tried just passing in an IntPtr and then trying to create an object from it?