Revit Element Collector

Revit Element Collector

Query the model through the fluent FilteredElementCollector wrappers in Nice3point.Revit.Extensions. They wrap the raw Revit collector API into a single readable chain, and keep filtering inside Revit's native database engine — which evaluates filters before elements are expanded into memory — instead of materializing every element and filtering with LINQ.

When to use

• Retrieving elements, types, or instances by class, category, or parameter value.
• Reviewing code that writes new FilteredElementCollector(document) by hand or filters collector output with .Where(...).
• Fetching just the first match or a count without loading the whole result set.

When not to use

• You already hold the element and only need to read or set its parameters — use revit-element-and-parameter-access.
• You need a specialized ElementFilter the extensions do not expose — fall back to a raw FilteredElementCollector with that filter.

Workflow

Step 1: Open a collector from the document

var collector = document.CollectElements(); // whole document
var viewScoped = document.CollectElements(view); // elements visible in a view
var restricted = document.CollectElements(elementIds); // a known id set

Step 2: Apply quick filters as generic, typed calls

Prefer the generic and multi-argument overloads over raw typeof filters.

var walls = document.CollectElements()
    .OfClass()
    .ToElements();

var openings = document.CollectElements()
    .OfCategories(BuiltInCategory.OST_Walls, BuiltInCategory.OST_Floors)
    .Instances() // only instances; use .Types() for element types
    .ToElements();

Step 3: Filter by parameter with native rules, not LINQ

WhereParameter builds a native ElementParameterFilter — evaluated at the database level before element expansion — then continues the collector chain.

var tallWalls = document.CollectElements()
    .OfClass()
    .WhereParameter(BuiltInParameter.WALL_USER_HEIGHT_PARAM).IsGreaterThan(3.0, 1e-6)
    .ToElements();

// BAD — loads every wall into memory, then filters
var tallWalls = new FilteredElementCollector(document)
    .OfClass(typeof(Wall))
    .Cast()
    .Where(wall => wall.get_Parameter(BuiltInParameter.WALL_USER_HEIGHT_PARAM).AsDouble() > 3.0);

Comparisons include Equals, IsGreaterThan/IsGreaterThanOrEqualTo, IsLessThan/IsLessThanOrEqualTo (with an optional double epsilon), Contains/StartsWith (and their Not… inversions), and HasValue.

Step 4: Terminate with the fast native path

Use the extension terminators instead of LINQ — they call Revit's native fast implementations (Count uses GetElementCount()).

var firstRoom = document.CollectElements().OfClass().FirstOrDefault();
var wallCount = document.CollectElements().OfClass().Count();
var hasLevels = document.CollectElements().OfClass().Any();

Step 5: Verify

1. The query builds the filter through collector methods, not .Where(...) over materialized elements.
2. A parameter comparison uses WhereParameter, not a post-collection predicate.
3. The terminator is a native call (ToElements, First, FirstOrDefault, Count, Any).

Validation

• [ ] The collector comes from document.CollectElements(...), not a hand-written new FilteredElementCollector(...).
• [ ] Class and category filters use the generic/multi-argument extensions.
• [ ] Parameter conditions use WhereParameter(...), keeping filtering at the database level.
• [ ] Single-result and count queries use First/FirstOrDefault/Count/Any, not LINQ.
• [ ] A quick filter (class/category) precedes a slow filter (parameter) to shrink the candidate set.

Common Pitfalls

| Pitfall | Correct approach | |------------------------------------------------------------------------------|-----------------------------------------------------------------------------| | .Where(element => element.get_Parameter(...).AsDouble() > x) after the collector | WhereParameter(param).IsGreaterThan(x, epsilon) — a native rule. | | collector.ToElements().Count / .Any() (LINQ over the list) | collector.Count() / collector.Any() — native fast paths. | | Comparing double parameters without an epsilon | Use the IsGreaterThan(value, epsilon) overload. | | CollectElements or WhereParameter not found | The Nice3point.Revit.Extensions package is not referenced in the project. | | Reusing one collector after a terminator | Start a fresh CollectElements() per query; terminators stop the iterator. |

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: Nice3point
• Source: Nice3point/revit-skills
• License: MIT

Install and usage instructions live in the source repository linked above.