Design time rendering and run time rendering.

I was doing some work on the GMap.Control over the weekend. On thing I found is that whenever I drop the control on the form, it always gives me an error on rendering, error to create control, error to render a control.

The problem is , when the visual studio render a control on the form, it will look for the DesignerAttribute, if it's not available, it will look for the default ControlDesigner. The ControlDesigner has a default method called GetDesignTimeHtml() , It will render the view on the form.

Use the reflector, here is what GetDesignTimeHtml() will do by default:

public virtual string GetDesignTimeHtml()
{
     StringWriter writer1 = new StringWriter(CultureInfo.InvariantCulture);
     DesignTimeHtmlTextWriter writer2 = new DesignTimeHtmlTextWriter(writer1);
     string text1 = null;
     bool flag1 = false;
     bool flag2 = true;
     Control control1 = null;
     try
     {
           control1 = this.ViewControl;
           flag2 = control1.Visible;
           if (!flag2)
           {
                 control1.Visible = true;
                 flag1 = !this.UsePreviewControl;
           }
           control1.RenderControl(writer2);
           text1 = writer1.ToString();
     }
     catch (Exception exception1)
     {
           text1 = this.GetErrorDesignTimeHtml(exception1);
     }
     finally
     {
           if (flag1)
           {
                 control1.Visible = flag2;
           }
     }
     if ((text1 != null) && (text1.Length != 0))
     {
           return text1;
     }
     return this.GetEmptyDesignTimeHtml();
}

Actaully, at the design time, a lot of objects are not initialized properly, so it will cause an exception.

So, I made an easy approach, I override the GetDesignTimeHtml() method to let it simply draw a string. Of course, there are a lot of more interesting stuff you can do here.

        public override string GetDesignTimeHtml()
       {
           try
           {
               StringBuilder sb = new System.Text.StringBuilder();
               sb.Append("GMap2 Server Control");
               return sb.ToString();
           }
           catch (Exception ex)
           {
               return GetErrorDesignTimeHtml(ex);
           }
       }

It at lease won't give me any error anymore.