C++ Example of an Unbound Dataset

C++ Example of an Unbound Dataset
/* This sample demonstrates the use of Datasets.Add and the
 * RequestData event supported by MapX to build an unbound
 * dataset, which allows MapX to access data whose format
 * is known only to the programmer. In this example, the
 * data is in the form of an array of structs in C++.
 */

// For help on handling events in C++, see "Handling MapX Events
// using C++" in the "Working with Visual C++" chapter.
BEGIN_EVENTSINK_MAP(CMapXView, CView)
  :
 ON_EVENT(CMapXView, IDC_MAP, MAPX_DISPID_REQUESTDATA, OnRequestData, VTS_BSTR VTS_I4 VTS_I2 VTS_PVARIANT VTS_PBOOL)

  :
END_EVENTSINK_MAP()
 :
 :
 :
const int kNumberOfRows = 3;
struct {
 char* stateName;
 double sales;
} theData[kNumberOfRows] = { {"NY", 100},
                             {"NH", 200},
                             {"VT", 300} };

void CMapXView::OnUnboundClick() {
 CMapXFields flds;
 CMapXDataset ds;
 COleVariant fldsVt;
 COptionalVariant optVt;

 try {
  // Zoom in on New England
  m_ctrlMapX.ZoomTo(800, -70.26, 44.05);

  // Create a new Fields object

  flds.CreateDispatch(flds.GetClsid());

  // Describe the structure of the unbound dataset:
  flds.Add(COleVariant("State"), COleVariant("State"),
   COleVariant((short)miAggregationIndividual),
   COleVariant((short)miTypeString));
  flds.Add(COleVariant("Sales"), COleVariant("Sales"),
   COleVariant((short)miAggregationSum),
   COleVariant((short)miTypeNumeric));

  // Point the fldsVt variant at our new Fields object
  fldsVt.vt = VT_DISPATCH;
  fldsVt.pdispVal = flds.m_lpDispatch;

  fldsVt.pdispVal->AddRef();

  // Create the unbound dataset. The "RequestData" event
  // will be triggered to get the data to be used.
  ds = m_ctrlMapX.GetDatasets().Add(miDataSetUnbound, optVt,
   COleVariant("My Dataset"), COleVariant("State"),
   optVt, COleVariant("USA"), fldsVt, optVt);

  // Create a theme based on the "Sales" column in the
  // unbound dataset
  ds.GetThemes().Add(miThemeRanged, "Sales", "My Theme");
 } catch (COleDispatchException *e) {

  e->ReportError();
  e->Delete();
 } catch (COleException *e) {
  e->ReportError();
  e->Delete();
 }
}

void CMapXView::OnRequestData(LPCTSTR DataSetName, long Row, short Field, VARIANT FAR* value, BOOL FAR* Done) {
 *Done = false;
 // Tell MapX to continue fetching data unless we've exceeded
 // the bounds of the dataset
 if(strcmp(DataSetName, "My Dataset") == 0 && Row > 0 && Row <= kNumberOfRows) {
  switch(Field) {
  case 1: // State field
   // copy the state string into the value variant.

   value->vt = VT_BSTR;
   value->bstrVal = CString(theData[Row-1].stateName).AllocSysString();
   break;
  case 2: // Sales field
   // copy the sales double into the value variant
   value->vt = VT_R8;
   value->dblVal = theData[Row-1].sales;
   break;
  }
 } else
  // Gone out of bounds... tell MapX to stop fetching
  *Done = true;
}