Selecting Elements in Revit API

 
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Selecting elements or geometries is a common requirement in Revit plugins. You might need users to select objects for various purposes: elements for further processing, points for placing families, or surfaces for calculations. All of that is possible by knowing the Selection class.
In this post:
  1. Accessing the Selection class
  2. Ways to get selected elements
  3. Applying a Selection Filter
  4. Setting selection
  5. Setting selection

Accessing the Selection class

The Selection class (from Autodesk.Revit.UI.Selection) is a gateway for retrieving already selected elements, setting new selections, and prompting users to select elements or geometries within your Revit plugins.
C#
var uiApp = commandData.Application;
var uiDoc = uiApp.ActiveUIDocument;
var doc = uiDoc.Document;

var selectionManager = uiDoc.Selection;

Ways to get selected elements

Revit API offers various ways to handle element selection:
•
Retrieving pre-selected elements:
Get elements that were selected before your method runs
•
Requesting user selection:
Prompt the user to select elements after your method starts (e.g., after a button click).
•
Mixed approach:
Retrieve already selected elements, or if no elements are selected, prompt the user for selection.

Retrieving pre-selected elements

To retrieve elements that were manually selected in the model before running your method, use the Selection.GetElementIds.
C#
var selectedElementsIds = selectionManager.GetElementIds();
TaskDialog.Show("Selected Elements", $"Selected elements number: {selectedElementsIds.Count}");

Requesting user selection

To request the user to select elements, you can use a variety of Pick[…] methods:
•
PickObject and PickObjects: select one or multiple elements of various types
Specify the Element type (Element, PointOnElement, Edge, Face, LinkedElement, Subelement) with the ObjectType enumerator.
•
PickPoint: select a point.
•
PickElementsByRectangle: select elements by drawing a rectangle on the screen.
C#
// Picking objects (Elements, geometries) - requesting the user to select
var elementReference = selectionManager.PickObject(ObjectType.Element, "Select element");
var element = doc.GetElement(elementReference);
TaskDialog.Show("Picked Element", $"Element: {element.Name}");

var elementsReferences = selectionManager.PickObjects(ObjectType.Element, "Select elements");
TaskDialog.Show("Picked Elements", $"Elements number: {elementsReferences.Count}");
	
// Picking an edge
Reference edgeRef = selectionManager.PickObject(ObjectType.Edge, "Select an edge");
Edge edge = doc.GetElement(edgeRef.ElementId).GetGeometryObjectFromReference(edgeRef) as Edge;
TaskDialog.Show("Picked Edge", $"Edge length: {edge.ApproximateLength}");

// Picking a point
var xyz = selectionManager.PickPoint(ObjectSnapTypes.Midpoints, "Select a midpoint");
TaskDialog.Show("Picked Point", $"Point coordinates: {xyz}");

// Picking elements by rectangle
var elementsSelected = selectionManager.PickElementsByRectangle("Select elements by rectangle");
var elementNames = string.Join(", ", elementsSelected.Select(e => e.Name));
TaskDialog.Show("Picked Elements by Rectangle", $"Elements: {elementNames}");

Mixed Approach: Retrieving or Requesting Selection

To enhance user experience, you can try to retrieve already selected elements or, if none are selected, prompt the user to make a selection.
C#
// Mixed approach -retrieving the selected elements or, if none are selected, requesting to select
var selectedElementsIds = selectionManager.GetElementIds();
if (selectedElementsIds.Count == 0)
{
	// Use the pick object method to select an element
	var elementsReferences = selectionManager.PickObjects(ObjectType.Element, "Select elements");
	selectedElementsIds = elementsReferences.Select(r => r.ElementId).ToList();
}
TaskDialog.Show("Selected Elements", $"Selected elements number: {selectedElementsIds.Count}");

Applying a Selection Filter

Sometimes, you need to set strict rules for elements available for selection. For example, you might want the user to select only walls of a certain width. In such cases, you can apply a Selection Filter.
To define a Selection Filter, create a class implementing the ISelectionFilter interface. Below are examples of two filters and their usage.
C#
// Applying the selection filter
var wallSelectionFilter = new ElementTypesSelectionFilter(typeof(Wall));
var wallReference = selectionManager.PickObject(ObjectType.Element, wallSelectionFilter, "Select a wall");

var wallAndFloorSelectionFilter = new ElementTypesSelectionFilter(typeof(Wall), typeof(Floor));
var wallOrFloorReference = selectionManager.PickObject(ObjectType.Element, wallAndFloorSelectionFilter, "Select a wall or a floor");

var minimumWidthWallSelectionFilter = new MinimumWidthWallsSelectionFilter(1); // remember - by default, width unit is Feet
var minimumWidthWallReference = selectionManager.PickObject(ObjectType.Element, minimumWidthWallSelectionFilter, "Select a wall with a minimum width of 1 foot");


// SelectionFilter classes
class ElementTypesSelectionFilter : ISelectionFilter
{
	private readonly Type[] allowedTypes;

	public ElementTypesSelectionFilter(params Type[] allowedTypes)
	{
		this.allowedTypes = allowedTypes;
	}

	public bool AllowElement(Element element)
	{
		return allowedTypes.Contains(element.GetType());
	}

	public bool AllowReference(Reference reference, XYZ position)
	{
		return false;
	}
}

class MinimumWidthWallsSelectionFilter : ISelectionFilter
{
	private readonly double minimumWidth;

	public MinimumWidthWallsSelectionFilter(double minimumWidth)
	{
		this.minimumWidth = minimumWidth;
	}

	public bool AllowElement(Element element)
	{
		if (element is Wall wall) return wall.Width >= minimumWidth;
			
		return false;
	}

	public bool AllowReference(Reference reference, XYZ position)
	{
		return false;
	}
}

Setting selection

Finally, if you need to set the selection programmatically within your method, use Selection.SetElementIds.
C#
var wallsIds = new FilteredElementCollector(doc)
.OfClass(typeof(Wall))
.WhereElementIsNotElementType()
.ToElementIds();

selectionManager.SetElementIds(wallsIds);

Setting selection

•
Use Selection class to:
◦
Retrieve pre-selected elements.
◦
Prompt users to select elements after your method starts.
◦
Combine both approaches for flexibility.
•
Apply a SelectionFilter to ensure users select elements that meet your criteria.
•
Set selections programmatically with Selection.SetElementIds.
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