The Building Coder: NewBlend Sample

Until now, The Building Coder included no example at all of using the NewBlend method. A developer ran into an issue using it, and my colleague Joe Ye created an external command to resolve the issue, so I took and added it. Here is the issue that prompted this:

Question: I am trying to create a blend with two circular profiles, but it is not working. Can you please provide some solution for us?

Answer: After several tests, I found that the issue is due to the fact that the top and bottom profiles should contain at least two curves.

I split the circle that you were using for you profile into two semi-circle arcs. Now the command successfully creates the new blend.

I used Joe's sample code to create a new Building Coder sample external command CmdNewBlend. It exercises the following helper method CreateBlend for the actual new blend creation:

static Blend CreateBlend( Document doc )
{
  Debug.Assert( doc.IsFamilyDocument,
    "this method will only work in a family document" );
 
  Application app = doc.Application;
 
  Autodesk.Revit.Creation.Application creApp 
    = app.Create;
 
  Autodesk.Revit.Creation.FamilyItemFactory factory 
    = doc.FamilyCreate;
 
  double startAngle = 0;
  double midAngle = Math.PI;
  double endAngle = 2 * Math.PI;
 
  XYZ xAxis = XYZ.BasisX;
  XYZ yAxis = XYZ.BasisY;
 
  XYZ center = XYZ.Zero;
  XYZ normal = -XYZ.BasisZ;
  double radius = 0.7579;
 
  Arc arc1 = creApp.NewArc( center, radius, 
    startAngle, midAngle, xAxis, yAxis );
 
  Arc arc2 = creApp.NewArc( center, radius, 
    midAngle, endAngle, xAxis, yAxis );
 
  CurveArray baseProfile = new CurveArray();
 
  baseProfile.Append( arc1 );
  baseProfile.Append( arc2 );
 
  XYZ center2 = new XYZ( 0, 0, 1.27 );
 
  Arc arc3 = creApp.NewArc( center2, radius, 
    startAngle, midAngle, xAxis, yAxis );
 
  Arc arc4 = creApp.NewArc( center2, radius, 
    midAngle, endAngle, xAxis, yAxis );
 
  CurveArray topProfile = new CurveArray();
 
  topProfile.Append( arc3 );
  topProfile.Append( arc4 );
 
  Plane basePlane = creApp.NewPlane( 
    normal, center );
 
  SketchPlane sketch = factory.NewSketchPlane( 
    basePlane );
 
  Blend blend = factory.NewBlend( true, 
    topProfile, baseProfile, sketch );
 
  return blend;
}

The command mainline simply checks that the current document is indeed a family document and then calls CreateBlend:

[Transaction( TransactionMode.Automatic )]
[Regeneration( RegenerationOption.Manual )]
class CmdNewBlend : IExternalCommand
{
  public Result Execute(
    ExternalCommandData commandData,
    ref string message,
    ElementSet elements )
  {
    UIApplication app = commandData.Application;
    Document doc = app.ActiveUIDocument.Document;
 
    if( doc.IsFamilyDocument )
    {
      Blend blend = CreateBlend( doc );
 
      return Result.Succeeded;
    }
    else
    {
      message = "Please run this command "
        + "in a family document.";
 
      return Result.Failed;
    }
  }
}

This is what the resulting blend looks like in the family editor:

I modified the code to create a more interesting shape using a skewed rectangle for the top profile like this:

  CurveArray topProfile = new CurveArray();
 
  bool circular_top = false;
 
  if( circular_top )
  {
    // create a circular top profile:
 
    XYZ center2 = new XYZ( 0, 0, 1.27 );
 
    Arc arc3 = creApp.NewArc( center2, radius,
      startAngle, midAngle, xAxis, yAxis );
 
    Arc arc4 = creApp.NewArc( center2, radius,
      midAngle, endAngle, xAxis, yAxis );
 
    topProfile.Append( arc3 );
    topProfile.Append( arc4 );
  }
  else
  {
    // create a skewed rectangle top profile:
 
    XYZ[] pts = new XYZ[] {
      new XYZ(0,0,3), 
      new XYZ(2,0,3), 
      new XYZ(3,2,3), 
      new XYZ(0,4,3)
    };
 
    for( int i = 0; i < 4; ++i )
    {
      topProfile.Append( creApp.NewLineBound(
        pts[0 == i ? 3 : i - 1], pts[i] ) );
    }
  }