IsCommandAvailable causes nullref exception

[john]

Ok, this is absolutely doing my head in as I have searched for countless examples all of which seem to suggest I'm not doing anything wrong... Basically, I just want to control the visibility/usability of my external command. Everywhere I've read suggests:

namespace HERibbon
{
    // [Transaction(TransactionMode.Manual)]
    [Regeneration(RegenerationOption.Manual)]
    public class Availability : IExternalCommandAvailability
    {
        public bool IsCommandAvailable(UIApplication uiApp, CategorySet catSet)
        {
            // if (catSet.IsEmpty) return true;
            // if (uiApp.ActiveUIDocument.Document.IsFamilyDocument) return false;
            // if (uiApp.ActiveUIDocument.Document.IsModifiable) return true;
            return true;
        }
    }
    class App : IExternalApplication
    {
        static void AddRibbonPanel(UIControlledApplication application)
        {
            // Create the ribbon tab
            String tabName = @"H&E Tools";
            application.CreateRibbonTab(tabName);

            // Create the panels on that tab
            RibbonPanel rp_About = application.CreateRibbonPanel(tabName, "About");

            // Get our installation path
            string thisAssemblyPath = Assembly.GetExecutingAssembly().Location;

            // Add to the About Panel
            // About
            PushButtonData pbData_About = new PushButtonData("About", "Info", thisAssemblyPath, "HETools.About");
            // pbData_About.AvailabilityClassName = "HERibbon.Availability";
            PushButton pb_About = rp_About.AddItem(pbData_About) as PushButton;
            pb_About.ToolTip = @"H&E Tools version info.";
            BitmapImage image_About = new BitmapImage(new Uri(@"C:\Program Files\HETools\src\about.ico"));
            pb_About.LargeImage = image_About;
            pb_About.Image = image_About;
            pb_About.AvailabilityClassName = "HERibbon.Availability";
        }

        public Result OnStartup(UIControlledApplication application)
        {
            AddRibbonPanel(application);
            return Result.Succeeded;
        }

        public Result OnShutdown(UIControlledApplication application)
        {
            return Result.Succeeded;
        }
    }
}

The commented out code are combos I've tried to get this thing to work.

The problem is when I select my tab on the ribbon when no document is open I get the following error: 

Debug says the exception is thrown at the public bool IsCommandAvailable. If I comment out the class, my plugin works fine. Even with the exception, the plugins still work once a project is opened, however, I need to fix this. My main plugin is a workshare enabler that I obviously can't have being run in the family editor (for example).

I have literally tried copying and pasting this sample and I still get a null ref error. I started from thebuildingcoder's zerodoc and am getting the same exception. I am absolutely out of ideas... has something changed in 2019?

[jeremytammik]

Dear John,

Thank you for your query.

Welcome to the digital world of programming.

Unfortunately, the computer will always just do what you tell it to.

Not what you want.

It normally takes a decade or two for a novice programmer to accept and get used to that hard fact.

Barring bugs in the libraries you use, of course, including and not limited to the Revit API.

Therefore, I personally prefer to DIY and just fight with my own bugs, whenever I can.

First of all, debug your code step by step to discover exactly which line throws the exception, so you can identify the null reference culprit. That will probably clear the problem right away.

Next: have you looked at this old sample of mine?

http://thebuildingcoder.typepad.com/blog/2011/02/enable-ribbon-items-in-zero-document-state.html

If that does not help, I would suggest the next step: search globally for IExternalCommandAvailability in the official Revit SDK samples, then in The Building Coder blog, then on the Internet in general.

I am sure there is a really easy fix, which will be totally obvious once you discover it.

I hope this helps.

Good luck!

Best regards,

Jeremy

[john]

Hi Jeremy,

Thanks for the reply. Per my post, I have debugged and the exception is thrown at the public bool.

And yes, again per my post, I have copied your example verbatim, and it threw the exact same error (hence me wondering if something has changed in 2019).

Appreciate the help.

[jeremytammik]

I'll see whether I can get it running in Revit 2019 for you...

[FAIR59]

there is a setting in the addin-manifest file [ NotVisibleWhenNoActiveDocument ] that will disable your  button when there is no document!

http://thebuildingcoder.typepad.com/blog/2010/05/addin-visibility-mode.html

[jeremytammik]

I migrated the ZeroDocPanel to Revit 2019 for you and encountered no problem with that whatsoever.

I debugged it, and the OnStartup and IsCommandAvailable methods are both called just as expected.

The external command is listed and can be executed in the external tools menu in zero document state:

 

The command execution displays the task dialogue:

 

So your problem is elsewhere, and you can restart from scratch with my updated sample to avoid it.

Good luck!

Cheers,

Jeremy

[jeremytammik]

Maybe you would like me to add the link?

https://github.com/jeremytammik/ZeroDocPanel

🙂

[jeremytammik]

Here is the blog post pointing out the update and the new “ZeroDocPanel GitHub repository:

http://thebuildingcoder.typepad.com/blog/2018/09/support-dlls-zero-document-state-and-forge-accelera...

Cheers,

Jeremy

[john]

Hi Jeremy,

I've downloaded your file, but haven't had the chance to implement it as yet (projects getting in the way). Given I have tried copying your code verbatim, I suspect the problem may lay elsewhere. I'll try commenting everything out and debugging one step at a time to see if I can isolate the cause.

I do appreciate you taking the time to have a look.

FAIR59 re: manifest file - I'm aware of this, though it is limiting. The plugins I've written - and one I have planned - will require a bit more flexibility. I'll need to get this working basically...

[john · Accepted solution]

I don't know why, but for some reason changing the UIControlledApplication var name from "application" to "uiApp" inexplicably fixed the issue.

public bool IsCommandAvailable(UIApplication uiApp, CategorySet catSet)
static void AddRibbonPanel(UIControlledApplication application)
public Result OnStartup(UIControlledApplication application)
public Result OnShutdown(UIControlledApplication application)

Bizarre.

[jeremytammik]

Dear John,

Thank you for your confirmation and congratulations to hear it is working now, however bizarre the resolution.

Cheers,

Jeremy