Using C# with the Inventor API (Part 1)

My last post contained VB.Net and C# versions of a VBA program from an earlier post.  Converting the VBA program to VB.Net was relatively easy.  The conversion to C# wasn’t as easy.  In this post I want to begin covering many of the issues you’ll run into when converting VBA code to C#.

One question that might come to mind is why would you want to convert from VBA and not just write everything in C# to begin with?  The first reason is that many of the programming samples you’ll find for the Inventor API are written using VBA.  The second reason is that VBA remains the fastest and easiest way to access and use the Inventor API.  Having said that, it does have a lot of other shortcomings so I wouldn’t recommend it for general development, but if you’re not using it for prototyping you’re missing out on a very powerful tool.

To go from VBA to C#, I’ve found the simplest method is to first convert the code to VB.Net.  This is typically fairly easy, particularly if the VBA code was written with going to VB.Net in mind.  For example, all arrays should be 0 based.  In many cases it’s just a copy and paste and Visual Studio will automatically do some syntax conversion.  Some of the manual changes that were required I went over in the previous post.  The next step is to go from VB.Net to C#.  There are some converters that do a pretty good job of automatically converting the VB.Net code to C#.  I found an online converter using Google that worked great.  (For any syntax issues that might still come up, here’s a good comparison of VB.Net and C#.)  Next you’ll need to account for other differences that are typically specific to a COM Automation API, like Inventor’s.  It’s those issues that this series of posts will attempt to cover.

Item Property
C# hides the fact that there’s an Item property on the Inventor collection objects so  you access the contents of the collection as if it was a read-only array, except the first item has an index of 1.

VBA

    Dim body As SurfaceBody 
    Set body = partDef.SurfaceBodies.Item(1)

C#

    SurfaceBody body;
    body = partDef.SurfaceBodies[1];

Comparing Two Objects
Sometimes you need to check if two variables referencing objects are referring to the same object.  Here’s how you do it in VBA and C#

VBA

    ' Get a parameter using two different collections.
    Dim var1 As Parameter
    Set var1 = partDef.Parameters.Item("Length")
    Dim var2 As ModelParameter
    Set var2 = partDef.Parameters.ModelParameters.Item("Length")  

    ' Verify that the variables are referencing the same parameter.
    If var1 Is var2 Then
        MsgBox "The two variables reference the same object."
    End If

C#

  // Get a parameter using two different collections. 
  Parameter var1 = partDef.Parameters["Length"]; 
  ModelParameter var2;
  var2 = partDef.Parameters.ModelParameters["Length"]; 

  // Verify that the variables are referencing the same parameter. 
  if (var1 == var2) 
  { 
    MessageBox.Show("The two variables reference the same object."); 
  }

Checking the Type of an Object
Sometimes it’s useful to be able to check if an object is a certain type.  Both VBA and C# provide an easy way to do this.

VBA

    ' Get the selected object. 
    ' This will fail if nothing is selected.
    Dim selectedObject As Object
    Set selectedObject = _
                   ThisApplication.ActiveDocument.SelectSet.Item(1)

    ' Check that the selected object is a sketch line.
    If TypeOf selectedObject Is SketchLine Then
        MsgBox "Selected object is a sketch line"
    Else
        MsgBox "Something besides a sketch line is selected."
    End If

C#

    // Get the selected object. 
    // This will fail if nothing is selected.
    object selectedObject = invApp.ActiveDocument.SelectSet[1];

    // Check that the selected object is a sketch line.
    if (selectedObject is SketchLine)
        MessageBox.Show("Selected object is a sketch line");
    else
        MessageBox.Show("Something besides a sketch line is
                         selected.");

Iterating Through the Contents of a Collection
Using a For Each loop is the most efficient way to iterate through the contents of a collection.  In some cases it can be much faster than using the collection’s Count and Item properties.

VBA

    ' Iterate over all of the faces in the primary body.
    Dim area As Double
    Dim partFace As Face
    For Each partFace In partDef.SurfaceBodies.Item(1).Faces
        area = area + partFace.Evaluator.area
    Next

    MsgBox "Total surface area: " & area & " cm^2"

C#

    // Iterate over all of the faces in the primary body.
    double area = 0;
    foreach( Face partFace in partDef.SurfaceBodies[1].Faces)
    {
        area += partFace.Evaluator.Area;
    }

    MessageBox.Show("Total surface area: " + area + " cm^2");

Comments

[Sonicsx]

Nice blog. Really useful. Maybe you can help me. What is the equivalence in c# of the code below?

Dim oPartDoc As PartDocument
Set oPartDoc = ThisApplication.Documents.Open("C:\work\1.ipt", False)

THX

[Joe]

Could you please explain why you would want to convert from VB .NET to C#?

[Rodney]

One thing to note with C# and the some members. There are a few types I've come across that don't properly expose some members and a get_MemberName() has to be used instead.

For example:
Parameter.Units -> Parameter.get_Units()
ComponentOccurences.ItemByName() -> ComponentOccurences.get_ItemByName()