CODEWITHSUNDEEP
c#revit-api
Madonna Remon
Madonna Remon

Reputation: 1219

Check if the element has a certain parameter in revit api

In Revit API, when you want to get a parameter, you send its enum then fetch it and you convert it to the type you want.

But sometimes the parameter is missing so it return null, and null.AsDouble() or null.AsValueString() throws a null exception.

I retrieve so many parameters and I am using ternary operators but I am not sure that this is the best way to handle this

string typemark = e.get_Parameter(BuiltInParameter.ALL_MODEL_TYPE_MARK)!=null?wt.get_Parameter(BuiltInParameter.ALL_MODEL_TYPE_MARK).AsValueString():"";
double cost = e.get_Parameter(BuiltInParameter.ALL_MODEL_COST)!=null?wt.get_Parameter(BuiltInParameter.ALL_MODEL_COST).AsDouble():0;

I was thinking of doing a function that is more generic, to pass the parameter and the type that I want to convert the result to.

public static T CheckParameterAndFetch<T>(this Element e, BuiltInParameter p, Type t)
    {
        if (e.get_Parameter(p) != null)
        {
            if (t.GetType() == typeof(string))
            {
                return (T)Convert.ChangeType(e.get_Parameter(p).AsValueString(), typeof(string));                   
            }
            else if (t.GetType() == typeof(double))
            {
                return (T)Convert.ChangeType(e.get_Parameter(p).AsDouble(), typeof(double));
            }
            else if (t.GetType() == typeof(int))
            {                  
                return (T)Convert.ChangeType((int)e.get_Parameter(p).AsDouble(), typeof(double));
            }
        }
        else
        {
            if (t.GetType() == typeof(string))
            {

                return (T)Convert.ChangeType("", typeof(string));
            }
            else if (t.GetType() == typeof(double))
            {
                return (T)Convert.ChangeType(0, typeof(double));
            }
            else if (t.GetType() == typeof(int))
            {
                return (T)Convert.ChangeType(0, typeof(int));

            }
        }
        return (T)Convert.ChangeType(null, typeof(string));
    }

and when calling it I type the following:

string typeName = wt.CheckParameterAndFetch(BuiltInParameter.ALL_MODEL_TYPE_NAME,typeof(string));

and I get this exception:

The type arguments for method 'namespace.Extensions.CheckParameterAndFetch (Autodesk.Revit.DB.Element, Autodesk.Revit.DB.BuiltInParameter, System.Type)' cannot be inferred from the usage. Try specifying the type arguments explicitly. (CS0411)

Upvotes: 1

Views: 2993

Answers (1)

konrad
konrad

Reputation: 3716

I think that with the latest .NET framework you can just call it like so: var param = v.get_Parameter(BuiltInParameter.ALL_MODEL_COST)?.AsInteger(); notice the '?' after the get_Parameter() call. That checks whether the parameter returned was null and will not call AsInteger() if it was null. Here's some more info:

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/null-conditional-operators

Upvotes: 1

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