Purging Viewport Types

In RevitAPI, filtering and collecting elements are present in almost every developed code for writing add-ins. Usually, we locate elements by their Category or class type using statements like this, for example when we want to retrieve all walls from the current document.

var elements = new FilteredElementCollector(doc).OfClass(typeof(Wall));
var elements = new FilteredElementCollector(doc).OfCategory(BuiltInCategory.OST_Walls);

The process becomes trickier when trying to find an element without a defined class, like Viewport Types. When we inspect a viewport using Revitlookup, we discover that the ViewportType is categorized as ElementType.

ElementType serves as a fundamental class for all Revit elements; hence, it is not helpful. Considering alternative approaches, one could explore the possibility of identifying purgable viewports indirectly by targeting existing parameters. For example, since ViewportType is a system family all must possess the "Show Extension Line" parameter BuiltInParameter.VIEWPORT_ATTR_SHOW_EXTENSION_LINE , we can use this parameter as a filter rule to identify all types that possess it. Fortunately, this parameter is a bool parameter, whose value is either 0 or 1, then we can use ParameterFilterRuleFactory.CreateGreaterOrEqualRule and supply a value of 0 for checking.

With a list of viewport types established, the next step involves iterating through each type to retrieve the associated viewports using the GetDependentElements(ElementFilter) method.

Here's an example to illustrate the process:

// https://forums.autodesk.com/t5/revit-api-forum/deleting-unpurgeable-viewport-types-through-api/td-p/8790238
[Description("Purge Viewports")]
public void PurgeViewPorts()
{
    try
    {
        var doc = RvtApi.Doc;
        // create filterRule to be used in collection
        var rule = ParameterFilterRuleFactory.CreateGreaterOrEqualRule(
            new ElementId(BuiltInParameter.VIEWPORT_ATTR_SHOW_EXTENSION_LINE),
            0
        );

        // get all elements that comply to this rule
        var viewPortTypes = new FilteredElementCollector(doc)
            .WhereElementIsElementType()
            .OfCategory(BuiltInCategory.INVALID)
            .WherePasses(new ElementParameterFilter(rule));

        // now for each viewportType find a viewport instance dependent
        List<ElementId> purgeableIds = new List<ElementId>();
        foreach (var viewportType in viewPortTypes)
        {
            var viewports = viewportType.GetDependentElements(
                new ElementCategoryFilter(BuiltInCategory.OST_Viewports)
            );
            if (!viewports.Any())
            {
                purgeableIds.Add(viewportType.Id);
            }
        }

        // show a list of all purgeable Ids
        MessageBox.Show(
            string.Join("\r\n", purgeableIds.Select(o => o.Value().ToString()))
        );
        // ... handle these ids
    }
    catch (Exception ex)
    {
        // something bad happened
    }

    return;
}