Programatically uncheck "V/G Overrides Model" parameter in a view template

[Anonymous]

Hello, everyone.

I'm writing an addin that would allow users to hide model categories in a given view when a view template's included "V/G Overrides Model" parameter would otherwise restrict them from doing so.

I wrote this snippet of code to disable the template's V/G Model Overrides on the current view. (If I can get this to work, I'll apply it to all views in doc) 

Transaction tr = new Transaction(doc, "Template Override");
tr.Start()
View current = doc.ActiveView;       
current.get_Parameter(BuiltInParameter.VIS_GRAPHICS_MODEL).Set(0);
tr.Commit();

Running this gives me the "Object reference not set to an instance of an object" exception. If I'm not accessing this built-in parameter correctly, why does this method typically work for other built-in parameters?

I'm still somewhat new to this API, so any help would be much appreciated. 

Thank you.

EDIT: I now know that the current view, itself, is not a template, but it has a template. So, how do I go about accessing and modifying its template?

[RPTHOMAS108]

The current view may not support model elements and therefore the parameter would not exist for that view type. You should therefore check for null separately rather that getting a parameter from an element and trying to set it on a single line. You can also inspect the View.ViewType property to see if the view likely contains the target parameter.

You can get the template of a view from the View.ViewTemplateID property of the view using Document.GetElement(View.ViewTemplateID). ViewTemplates share the same class as the view types they are applicable to (the View.IsTemplate property identifies if it is a template).

When you are collecting views from filtered element collectors etc. it is important to exclude view template objects from such a collection (unless you intended to include them).

[Anonymous]

Thanks for the advice, RPTHOMAS108.

I wrote the following code to check for null templates and parameters:

View cur = doc.ActiveView;
                if (!cur.IsTemplate)
                {
                    ElementId elid = cur.ViewTemplateId;
                    if (doc.GetElement(elid) != null)
                    {
                        TaskDialog.Show("Non-null template", cur.Name);
                        ParameterSet ps = doc.GetElement(elid).Parameters;
                        Parameter vgm = null;
                        foreach (Parameter p in ps)
                        {
                            if (p.Id == doc.GetElement(elid).get_Parameter(BuiltInParameter.VIS_GRAPHICS_MODEL).Id)
                            {
                                vgm = p;
                                break;
                            }
                        }
                        if (vgm != null)
                        {
                            TaskDialog.Show(vgm.ToString() + " - Non-null parameter", cur.Name);
                            vgm.Set(0);
                        }
                        else if (doc.GetElement(elid).get_Parameter(BuiltInParameter.VIS_GRAPHICS_MODEL) == null) TaskDialog.Show("V/G Overrides Model - Null parameter", cur.Name);
                    }
                    else if (doc.GetElement(elid) == null) TaskDialog.Show("Null template", cur.Name);
                }

I've found that this code

doc.GetElement(elid).get_Parameter(BuiltInParameter.VIS_GRAPHICS_MODEL).Id

causes the exception, so I used BIP Checker to look at the VIS_GRAPHICS_MODEL parameter in the current view's template. 

I found that slightly more than half of these parameters in the "Graphics" parameter group are of type "None" and, thus, don't have a string value associated with them. I realized that this is due to the fact that these template parameters hold the visibility graphics settings for categories rather than a simple string value. All I want to do, however, is set the "Include" toggle for the parameter, rather than the non-existent string value:

From this post, it seems that the API does not yet allow this. But, again, I'm still in the process of learning the API, so if anyone knows of a workaround for this, I would greatly appreciate it. 

Thank you.

[FAIR59 · Accepted solution]

a View template has a List of Parameter Id's that are non-controlled by the template.

You have to add or remove the parameter Id for BuiltInParameter.VIS_GRAPHICS_MODEL from that List.

			View actView = doc.ActiveView;
			View template = null;
			if (actView.ViewTemplateId!= ElementId.InvalidElementId) template =doc.GetElement( actView.ViewTemplateId) as View;
			if (template==null) return;
			ElementId VGModel_ID = ElementId.InvalidElementId;
			List<ElementId> nonControledParams = template.GetNonControlledTemplateParameterIds().ToList();
			foreach ( var id in nonControledParams)
			{
				if (id.IntegerValue == (int) BuiltInParameter.VIS_GRAPHICS_MODEL)
				{
					VGModel_ID = id;
					break;
				}
			}
			using (Transaction t = new Transaction(doc,"change template"))
			{
					t.Start();
					// include VGModel
					if (VGModel_ID != ElementId.InvalidElementId)
					    {
						    nonControledParams.Remove(VGModel_ID);
							template.SetNonControlledTemplateParameterIds(nonControledParams);
					    }
					// exclude VGModel
					if (VGModel_ID == ElementId.InvalidElementId)
					    {
							nonControledParams.Add( new ElementId( BuiltInParameter.VIS_GRAPHICS_MODEL));
							template.SetNonControlledTemplateParameterIds(nonControledParams);
					    }
					//
					t.Commit();
			}

[Anonymous]

Thank you very much, FAIR59. The SetNonControlledTemplateParameterIds() method is exactly what I needed. 

I was able to apply this to all view templates in the current document with the following code:

UIApplication application = commandData.Application;
Document doc = application.ActiveUIDocument.Document;
            
FilteredElementCollector views = new FilteredElementCollector(doc).OfClass(typeof(View));
            
View template = null;
View cur = null;
try {
    foreach(var current in views.Reverse())
    {
        cur = current as View;
        if (!cur.IsTemplate)
        {
            if (cur.ViewTemplateId != ElementId.InvalidElementId) template = doc.GetElement(cur.ViewTemplateId) as View;
            else continue;

            ElementId VGModel_ID = ElementId.InvalidElementId;
            List<ElementId> nonControledParams = template.GetNonControlledTemplateParameterIds().ToList();
            foreach (var id in nonControledParams)
            {
                if (id.IntegerValue == (int)BuiltInParameter.VIS_GRAPHICS_MODEL)
                {
                    VGModel_ID = id;
                    break;
                }
            }
            using (Transaction t = new Transaction(doc, "Change Template"))
            {
                t.Start();
                if (VGModel_ID == ElementId.InvalidElementId)
                {
                    nonControledParams.Add(new ElementId(BuiltInParameter.VIS_GRAPHICS_MODEL));
                    template.SetNonControlledTemplateParameterIds(nonControledParams);
                }
                t.Commit();
            }
        }
    }
}
catch(Exception e)
{
    TaskDialog.Show("Exception", e.Message);
}