ArcGIS Pro 2.7 API Reference Guide
AddPoint Method (MultipointBuilderEx)
Example 

ArcGIS.Core.Geometry Namespace > MultipointBuilderEx Class : AddPoint Method
The MapPoint to add. It cannot be null.
A convenience method to add a MapPoint.
Syntax
public void AddPoint( 
   MapPoint point
)
Public Sub AddPoint( _
   ByVal point As MapPoint _
) 

Parameters

point
The MapPoint to add. It cannot be null.
Exceptions
ExceptionDescription
The input point is null.
Remarks
The XY-coordinates of the point are added to the end of the Coords list. If the point property HasZ is true, and this builder property HasZ is true, then the Z-value of the point is added to the end of the Zs list. The same is true for Ms and IDs. If the point is missing any of the attributes (Z, M, or ID) that are present in this builder, a default value is used. The default value for Z is zero, M is NaN, and ID is zero. If a point has an attribute that is missing in the builder, the attribute is ignored.
Example
// Builder constructors need to run on the MCT.
ArcGIS.Desktop.Framework.Threading.Tasks.QueuedTask.Run(() =>
{
  // assume a multiPoint has been built from 4 points
  // the modified multiPoint will have the first point removed and the last point moved

  using (MultipointBuilder mpb = new MultipointBuilder(multipoint))
  {
    // remove the first point
    mpb.RemovePoint(0);

    // modify the coordinates of the last point
    MapPoint pt = mpb.GetMapPoint(mpb.PointCount - 1);
    mpb.RemovePoint(mpb.PointCount - 1);

    MapPoint newPt = MapPointBuilder.CreateMapPoint(pt.X + 1.0, pt.Y + 2.0);
    mpb.Add(newPt);

    Multipoint modifiedMultiPoint = mpb.ToGeometry();
  }
});


// or use the builderEx constructors = don't need to run on the MCT.
MultipointBuilderEx builderEx = new MultipointBuilderEx(multipoint);
// remove the first point
builderEx.RemovePoint(0);
// modify the coordinates of the last point
var ptEx = builderEx.GetPoint(builderEx.PointCount - 1);
builderEx.RemovePoint(builderEx.PointCount - 1);

var newPtEx = MapPointBuilder.CreateMapPoint(ptEx.X + 1.0, ptEx.Y + 2.0);
builderEx.AddPoint(newPtEx);
Multipoint modifiedMultiPointEx = builderEx.ToGeometry() as Multipoint;
Requirements

Target Platforms: Windows 10, Windows 8.1

See Also

Reference

MultipointBuilderEx Class
MultipointBuilderEx Members