Parameters

Revit provides a general mechanism for giving each element a set of parameters that you can edit.

In the Revit UI, some element parameters are visible in the Element Properties Palette. The following sections describe how to get and use built-in parameters, shared parameters and global parameters.

In the Revit Platform API, Parameters are managed in the Element class. You can access Parameters in these ways:

Common ways to get the value of a parameter are shown below. In this sample, all three lines of code get the same parameter. Because this parameter is stored as a string, the AsString() method is used to get its value.

private void GetStringParameterValue(Wall wall)
{
    string s1 = wall.LookupParameter("Comments").AsString();
    string s2 = wall.GetParameter(ParameterTypeId.AllModelInstanceComments).AsString();
    string s3 = wall.get_Parameter(BuiltInParameter.ALL_MODEL_INSTANCE_COMMENTS).AsString();
}

Other ways to get a parameter are:

• By iterating through the Element.Parameters collection of all parameters for an Element (for an example, see the sample code in Walkthrough Get Selected Element Parameters).
• By iterating through the collection returned by Element.GetOrderedParameters(), which returns only parameters visible in the Properties Palette.
• By accessing a parameter by name via the Element.ParametersMap collection or Element.GetParameters()

You can retrieve the Parameter object from an Element using the overloaded Parameter property if you know the built-in ID, definition, or GUID. The Parameter[GUID] property overload gets a shared parameter based on its Global Unique ID (GUID), which is assigned to the shared parameter when it's created.

The Element.LookupParameter() method gets a parameter based on its localized name, so your code should handle different languages if it's going to look up parameters by name and needs to run in more than one locale. Also, keep in mind that multiple matches of parameters with the same name can occur because shared parameters or project parameters can be bound to an element category even if there is already a built-in parameter with the same name. For this reason, it is better to use Element.GetParameters() which will return all parameters matching the given name. Element.LookupParameter() will return the first match found.

Parameters Service

Parameters Service is a semi-automated, fully searchable database of design element parameters. Because Parameters Service lives in the Autodesk Construction Cloud, you can easily share it with teammates regardless of their physical location.

The class Autodesk.Revit.DB.ParameterDownloadOptions is an option class used for downloading parameters from the Parameters Service with the following properties:

• ParameterDownloadOptions.Categories - Categories for binding.
• ParameterDownloadOptions.IsInstance - Returns true if binding to element instances, false if binding to element types.
• ParameterDownloadOptions.Visible - Returns true if the parameter is visible to the user, false if it is hidden and accessible only via the API.
• ParameterDownloadOptions.GroupTypeId - Properties palette group identifier.

These ParameterUtils methods provide functionality relevant to the Parameters Service:

• ParameterUtils.DownloadParameter() - Allows users to create a shared parameter element in the given document according to a parameter definition downloaded from the Parameters Service.
• ParameterUtils.DownloadParameterOptions() - Allows users to retrieve the requested parameter's category, visibility and group bindings from the Forge Schema Service.
• ParameterUtils.DownloadCompanyName() - Allows users to download and record the name of the given parameter schema identifier's owning account in the given document.