.Net WinForms Design Time Rules

using System;
using System.ComponentModel;
using System.Windows.Forms;

namespace Test
{
    public class ComponentClass : Component
    {
        public ComponentClass()
        {
            MessageBox.Show("Runtime!");
        }
    }
}

using System;
using System.ComponentModel;
using System.Windows.Forms;

namespace Test
{
    public class ComponentClass : Component
    {
        public ComponentClass()
        {
            if (LicenseManager.UsageMode != LicenseUsageMode.Designtime)
            {
                MessageBox.Show("Runtime!");
            }
        }
    }
}

public static bool DesignMode
{
    get {  return (System.Diagnostics.Process.GetCurrentProcess().ProcessName == "devenv"); }
}

if (!DesignMode)
{
    // Run code that breaks in VS Designer (like trying to get a DB connection)
}

public static bool IsAnyInDesignMode(Control control){
    while(control != null){
        if(control.Site != null && control.Site.DesignMode)
            return true;
        control = control.Parent;
    }
    return false;
}