Sets the default family type id for the given family category. 
   Namespace:   Autodesk.Revit.DB  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
  Since:  2015 
Syntax
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Parameters
- familyCategoryId
 -  Type:  Autodesk.Revit.DB ElementId  
The family category id. 
- familyTypeId
 -  Type:  Autodesk.Revit.DB ElementId  
The default family type id. 
Examples
private void SetDefaultTypeFromDoor(Document document, FamilyInstance door)
{
    ElementId doorCategoryId = new ElementId(BuiltInCategory.OST_Doors);
    // It is necessary to test the type suitability to be a default family type, for not every type can be set as default. 
    // Trying to set a non-qualifying default type will cause an exception
    if (door.Symbol.IsValidDefaultFamilyType(doorCategoryId))
    {
        document.SetDefaultFamilyTypeId(doorCategoryId, door.Symbol.Id);
    }
} Private Sub SetDefaultTypeFromDoor(document As Document, door As FamilyInstance)
    Dim doorCategoryId As New ElementId(BuiltInCategory.OST_Doors)
    ' It is necessary to test the type suitability to be a default family type, for not every type can be set as default. 
    ' Trying to set a non-qualifying default type will cause an exception
    If door.Symbol.IsValidDefaultFamilyType(doorCategoryId) Then
        document.SetDefaultFamilyTypeId(doorCategoryId, door.Symbol.Id)
    End If
End Sub Exceptions
| Exception | Condition | 
|---|---|
| Autodesk.Revit.Exceptions ArgumentException | The family type id familyTypeId is invalid for the give family category familyCategoryId. | 
| Autodesk.Revit.Exceptions ArgumentNullException | A non-optional argument was NULL |