Why feature.shape can't use multipoint type?

Question

               IPointCollection pointcollection = new MultipointClass();              
                p.PutCoords(x.lon, x.lat);
                pointcollection.AddPoint(p);
                IGeometry geometry = pointcollection as IGeometry;
                 featureBuffer.Shape = geometry;//error here This geometry 
                                                   type is not supported

If I want to add lots of point features, what else can I do?

Answer 1

I think you're having trouble because IPointCollection does't implement IGeometry or because you haven't set the spatial reference property, to add lots of points to a point collection as a multipoint, assuming your X and Y values are stored as an array or list:

object gMissing = System.Type.Missing;

IMultipoint pMulPoint =  new MultipointClass();
IPointCollection pointcollection = pMulPoint as IPointCollection;

for (index = 0;index < pointcount;index++)
{
  IPoint p = new PointClass(); // important!
  p.PutCoords(x[index],y[index]);
  pointcollection.AddPoint(p, ref missing, ref missing);
}
IGeometry Geom = (IGeometry)pMulPoint;
Geom.SpatialReference = yourSpatialReference; // important!

See an example at https://resources.arcgis.com/en/help/arcobjects-net/conceptualhelp/index.html#/d/000100000mrv000000.htm not that I deal with multipoints much, usually I deal with point, polyline or polygon objects, but multipoints are a special case not needing to proceed via IGeometryCollection to an IGeometry.

However this assumes your feature class is of type Multipoint, if it's of type Point then you can't store a multipoint in the same way you can't put polygons or polylines or TINs or rasters into the feature class... they're the wrong sort of geometry to fit in the assigned space.

If you're creating point features in a point feature class then simply:

IPoint p = new PointClass();
p.PutCoords(x.lon, x.lat);
p.SpatialReference = yourSpatialReference; // important!
featureBuffer.Shape = p;