Custom UserControl generates Common Language Runtime error when added to a parent UC

Question

intro: I'm trying to create a custom control for use within autocad through autocad .net API.

I've created the basic design of the UC, and decided to group some elements of it in a custom UC and call it later to the main UC. (basically for code management, organisation... leaving me with a code structure like this:

UC(top)-consisting of few custom child UCs each of those Child UCs consisting of few buttons, and combo boxes.

simple so far...

in those child UCs, I call on a simple ACAD method/object.

the problem appears when I try adding one of those Child UCs to the main UC. I get a "CLR error" (image appended).

https://s32.postimg.org/6gnt3sgz9/why_no_work.jpg

I've tried few methods of solving the problem; 1) Using the Custom Controls instead of UC 2) tried to clear solution, rebuild solution. 3) tried creating a separate Class that calls on ACAD methods from outside the UC code

basically, what I've learned is, that I can (somehow) get the program to work if I run the code from within user created events (such as button click,...), but if I try calling acad command from within UC constructor, or UC_Load event method, I end up getting the CLR error when ever I try adding the childUC (through VSdesigner, and if I add it by code, I end up raising the error whenver I try calling on the designer)

if nothing else, I'd like to know why the code behaves differently depending if the code is called from "UC_load" or "button_clicked".

here's my code:

public partial class child : UserControl
{

    public child()
    {
        InitializeComponent();
        //if I initialize doc here, I get the error
    }

    private void child_Load(object sender, EventArgs e)
    {
        //if I initialize doc here, I get the error

    }

    private void button1_Click(object sender, EventArgs e)
    {
        //it works here, but Im unsure why
        Document doc = Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument;
    }
}

"the Document doc =..... is the line that generates the error;

Here's an image of the error, and the solution. The error appears when I klik the child object to the designer, or before I open the designer after I've added the "child object" from the code.

using C# acad 2017, VS2015, x64

Answer 1

Is this happening while you're creating the form, right?

This might happen as VS tried to load the object (in your case, the AutoCAD Document object), which is not possible, but might also happen as VS is 32 and AutoCAD references are 64. Consider use the AutoCAD references from the ObjectARX SDK, as these DLLs are just the method stubs.

I would suggest (as a best practice) to do not use AutoCAD objects inside the form, but rather separate UI and biz logic. Separation of UI and biz logic means, at least, have a class that is purely based on UI components (e.g. Windows.Form namespace), another class that implementes the actual AutoCAD command (i.e. AcMgd.dll & AcCoreMgd.dll objects) and, finally, the data layer (i.e. AcDbMgd.dll objects)