Tutorial 1: Reading the Model

Learn to use FilteredElementCollector to find and count elements in your Revit model.

Finished Script: 03_Tutorials/RevitAPI_Fundamentals/01_ReadingTheModel.cs

🎯 What You'll Learn

• FilteredElementCollector - the foundation of querying
• BuiltInCategory enumeration
• foreach loops for iterating collections
• The var keyword for type inference

The Collector Pattern

Every Revit API script that needs to find elements uses FilteredElementCollector:

var elements = new FilteredElementCollector(Doc)
    .OfCategory(BuiltInCategory.OST_Walls)
    .WhereElementIsNotElementType()
    .ToElements();

Let's break this down:

Method	Purpose
FilteredElementCollector(Doc)	Start a query on the document
.OfCategory(...)	Filter by category (Walls, Doors, etc.)
.WhereElementIsNotElementType()	Get instances, not types
.ToElements()	Execute the query and return results

Step 1: Count All Elements of a Category

var walls = new FilteredElementCollector(Doc)
    .OfCategory(BuiltInCategory.OST_Walls)
    .WhereElementIsNotElementType()
    .ToElements();

Println($"Total walls in project: {walls.Count}");

Step 2: Count Elements in Active View Only

Pass the view ID as the second argument:

var viewWalls = new FilteredElementCollector(Doc, Doc.ActiveView.Id)
    .OfCategory(BuiltInCategory.OST_Walls)
    .WhereElementIsNotElementType()
    .GetElementCount();

Println($"Walls in active view: {viewWalls}");

Step 3: Loop Through Elements with foreach

foreach (var wall in walls)
{
    Println($"Wall: {wall.Name}, ID: {wall.Id}");
}

The foreach loop:

• Iterates through each item in a collection
• var wall is the current item
• The code inside { } runs once per item

Step 4: Build a Data Table

Create structured output using anonymous objects:

var tableData = new List<object>();

foreach (var element in elements)
{
    tableData.Add(new
    {
        ID = element.Id.Value,
        Name = element.Name,
        Category = element.Category?.Name ?? "N/A"
    });
}

Table(tableData);

💡 Try This

1. Try different categories: OST_Doors, OST_Rooms, OST_Floors
2. Add the element's Level to the table output
3. Filter to only show elements with a specific name pattern

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Next: Tutorial 2: Parameters Deep Dive →