TImageEnVect.ObjectsCount
 
Declaration
property ObjectsCount: integer; (Read-Only)
Description
Read ObjectsCount to determine the number of objects in the TImageEnVect component. Use 
GetObjFromIndex to convert the index value to an Obj.
// Delete the objects of the specified layer
procedure DeleteObjectsOfLayer(iLayer : Integer);
var
  i: integer;
  ihobj: integer;
  iobjLayer: integer;
begin
  for i := ImageEnVect1.ObjectsCount - 1 downto 0 do
  begin
    ihobj := ImageEnVect1.GetObjFromIndex(i);
    // if hobj is on current layer then delete the object
    iobjLayer := ImageEnVect1.ObjLayer[ihobj];
    if iobjLayer = iLayer then
      ImageEnVect1.RemoveObject(ihobj);
  end;
  ImageEnVect1.Update();
end;
Transition Information
If you are transitioning your code to 
TImageEnView Layers, instead of ObjectsCount, use: 
TImageEnView.LayersCount.
Note: LayersCount also includes the background layer. So it is always >= 1
n := ImageEnView1.LayersCount;