Visual Studio designer crashes when overrideing WndProc

Question

I have a control inherited from System.Windows.Forms.Control which has the WndProc function overridden to pass the messages to an external DLL. The function looks like

public class GraphicsPanel : Control
{
        bool designMode;
        EngineWrapper Engine;

        public GraphicsPanel()
        {
            designMode = (LicenseManager.UsageMode == LicenseUsageMode.Designtime);
            this.SetStyle(ControlStyles.Selectable, true);
            this.TabStop = true;
        }

        public void SetEngine(EngineWrapper Engine)
        {
            this.Engine = Engine;
        }
    
        protected override void WndProc(ref Message m)
        {
            base.WndProc(ref m);

            if(designMode) // Tried this option
                return;

            if (!designMode && Engine != null) // And this option
                Engine.ProcessWindowMessage(m.Msg, m.WParam, m.LParam);
        }
}

If I have any mention of Engine in this function, it crashes because the external DLL apparently isn't loaded when the designer is displayed. I get the error message "Could not load file or assembly "..." or one of its dependencies.

I certainly should add that this code all works at run-time just not design-time. It's annoying having to comment out the two Engine lines of code whenever I want to use the designer.

Any advice for how to get the designer to work correctly while including this line of code.

enter image description here

score 2 · Answer 1 · edited May 23 '17 at 12:20

2

Do you need the WndProc to be executed in design-time? If not, you can try by adding a condition to the if:

bool designMode = (LicenseManager.UsageMode == LicenseUsageMode.Designtime);
if (!designMode && Engine != null)
    ...

You will need System.ComponentModel namespace imported.

Detecting design mode from a Control's constructor

edited May 23 '17 at 12:20

Community

1
1

answered Oct 22 '14 at 05:49

thepirat000

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Is there a compiler directive to do the same thing? This is certainly a good tid-bit to know, but it didn't solve the designer error. – Russell Trahan Oct 22 '14 at 06:09
I don't think so, check [this](http://stackoverflow.com/questions/4821682/design-mode-preprocessor-directive). Are you saying that `designMode` is false in design-time? Can you supply more information about the error? – thepirat000 Oct 22 '14 at 06:13
designMode is correct, but since the variable Engine is referencing this other dll which isn't loaded it can't compile for the designer. – Russell Trahan Oct 22 '14 at 06:28
How is `Engine` defined/created? – thepirat000 Oct 22 '14 at 06:30
It is a reference to an object defined in the dll. It is created at run-time thus the null check. – Russell Trahan Oct 22 '14 at 06:33
Ok. Is that DLL referenced in the project or you load it at run-time? – thepirat000 Oct 22 '14 at 06:35
It is referenced in the project. Nothing run-time except the creation of the Engine object after the control is created. – Russell Trahan Oct 22 '14 at 06:36
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/63459/discussion-between-thepirat000-and-russell-trahan). – thepirat000 Oct 22 '14 at 06:40

score 0 · Accepted Answer · answered Oct 22 '14 at 06:51

I solved this by moving the Engine references to a different function. This is odd but it works.

    void PassMessage(Message m)
    {
        if (Engine != null)
            Engine.ProcessWindowMessage(m.Msg, m.WParam, m.LParam);
    }

    protected override void WndProc(ref Message m)
    {
        base.WndProc(ref m);

        if (!designMode)
            PassMessage(m);
    }

Visual Studio designer crashes when overrideing WndProc

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