How do I make add-in using out from opened document?

[XARMA]

I have saw some add-in that can be used without opening rvt file.

How do I make add-in using out from opened document?

I face some error message, If I execute my dll file eventhough any simple codes it is.

Syetem.NullReferenceException: Object reference not set to an instance of an object at A.Command.Execute(ExternalCommandData commandData, String& message, ElementSet elements) at ...

[naveen.kumar.t · Accepted solution]

Hi @XARMA ,

If you want logic that runs when Revit starts (before any file is opened), implement IExternalApplication and use OnStartup:

public class MyApp : IExternalApplication
{
    public Result OnStartup(UIControlledApplication application)
    {
        // Add UI or run logic here
        return Result.Succeeded;
    }

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

Also, please take a look at the links 

https://help.autodesk.com/view/RVT/2024/ENU/?guid=Revit_API_Revit_API_Developers_Guide_Introduction_... 

If this doesn't help, Could you please explain your issue in more detail?