Tutorial 4: Element Selection

Learn how to let the user "Pick" elements from the model, using Paracore's Strongly Typed Selection to safely get exactly what you need.

Finished Script: 03_Tutorials/Paracore_Fundamentals/04_ElementSelection.cs

What You'll Learn

• The [Select] attribute
• Strongly Typed Selection: Asking for a Wall instead of a generic ID
• Modifying element parameters

Step 1: Define Inputs (The Smart Way)

In the past, you had to ask for a generic Reference or long (Element ID) and then manually find the object. With Paracore Hydration, you just ask for the type you want.

public class Params
{
    /// <summary>Select a Wall in Revit</summary>
    [Select(SelectionType.Element)]
    [Mandatory]
    public Wall TargetWall { get; set; }
    
    /// <summary>New comment text</summary>
    public string Comment { get; set; } = "Updated by Paracore";
}

Notice public Wall TargetWall. Without any attributes, this would normally render a Wall dropdown. But because of the [Select(SelectionType.Element)] attribute, Paracore:

1. Replaces the dropdown with a "Pick" button.
2. Filters the selection so they can only pick a wall.
3. Returns the actual Wall object to your script.

Step 2: Validate the Selection

Even though Paracore filters selection, the user might cancel or something might go wrong. Always check for null.

var p = new Params();

if (p.TargetWall == null)
{
    Println("No wall selected.");
    return;
}

Note: We don't need Doc.GetElement(id). We already have p.TargetWall!

Step 3: Modify the Element

Let's update the comments on the selected wall.

Transact("Update Wall Comment", () => {
    // Modify the real Wall object directly
    var param = p.TargetWall.get_Parameter(BuiltInParameter.ALL_MODEL_INSTANCE_COMMENTS);
    param?.Set(p.Comment);
    
    Println($"Updated Wall {p.TargetWall.Id} with comment: {p.Comment}");
});

Step 4: Run and Verify

1. Click the "Pick" button next to TargetWall.
2. The Paracore window will minimize.
3. Try to pick a Floor or Window -> Revit won't let you!
4. Pick a Wall.
5. Enter a comment and click Run Script.
6. Select the wall in Revit and check its properties.

Try This

1. Change public Wall to public Floor and see how the UI pick filter automatically restricts selection to floors.
2. Loadable Families: Note that there is no Window or Door class in Revit—they are FamilyInstances! For picking loadable components from the model, you use a Reference (which inherently provides a "Pick" button that lets you pick any element). To restrict it specifically to Windows, constrain it using the [RevitElements] attribute:

   [RevitElements(Category = "Windows")]
   public Reference WindowRef { get; set; }

   The Reference type inherently gives you the Pick button, while the Category constraint ensures you can only select Window instances!
3. Geometry and Points: Just like Reference, geometric types inherently provide a Pick button in the Paracore UI. No [Select] attribute is needed!

   public XYZ? MyPoint { get; set; } // Lets you pick a 3D point in space.
   public Edge SelectedEdge { get; set; } // Lets you pick a geometric edge.
   public Face SelectedFace { get; set; } // Lets you pick a geometric face.

Next: Tutorial 5: Modular Projects ->