Question

I’ve got a Compact Framework (3.5) control and I’d like it have a default color of SystemColors.Window, similar in apprearance to an edit control. The problem I’m having is Visual Studio (2008) always renders that control on the design surface with a default BackColor of Control. I assume it is either pulling it from the default back color of the base Control, from the parent, or from the Site.

Anyone have any idea how to specify or otherwise inform Visual Studio what the default BackColor should be?

public class MoneyInput : Control
{

    public MoneyInput()
    {            
        base.BackColor = SystemColors.Window;
        base.ForeColor = SystemColors.WindowText;
    }

    public override Color BackColor
    {
        get
        {
            return base.BackColor;
        }
        set
        {
            base.BackColor = value;
            Repaint();                
        }
    }

}

And here is the appropriate section of my DesignTimeAttributes.xmta file. Note that I don’t really want the default color to White as you see below, I was just trying to get anything to work:

<DesktopCompatible>true</DesktopCompatible>

<Property Name="BackColor">

  <Browsable>true</Browsable>

  <DesignerSerializationVisibility>
    DesignerSerializationVisibility.Visible
  </DesignerSerializationVisibility>

  <DefaultValue>
    <Type>System.Drawing.Color</Type>
    <Value>System.Drawing.Color.White</Value>
  </DefaultValue>

  <Category>Appearance</Category>

  <Description>The background color of the control</Description>

</Property>

Just to add some more progress (or lack thereof), I added a log to the control so that I can see what is going on when I drop the control on the design surface. The write to the BackColor in the constructor does take effect and changes the color from Control to Window. But then something in the designer infrastructure sets the color (via the property) back to Control. This happens after the ctor but before the OnResize and OnHandleCreated. Now if the control serialized the BackColor property into the designer with the correct value then it would be safely set back, but the designer doesn’t contain default values.

One last edit, I think the default value syntax for specifiying an enum (as opposed to a base type) is not correct. I am using the solution I posted below, but it is a hack and hopefully the next person that comes along can solve it for real.

Answer 1

I’m hoping to get a real answer still, but I’ll put down here my work-around solution:

public class MoneyInput : Control 
{

  // workaround for colors
  private bool _constructed = false;
  private int _handlesCreated; 


  public MoneyInput()
  {
      this.BackColor = SystemColors.Window;
      this.ForeColor = SystemColors.WindowText;
      _constructed = true;
  }

  public override Color BackColor
  {
      get
      {
          return base.BackColor;
      }
      set
      {
          // The logic below is based on:
          //
          // 1.  If not _constructed then we are getting called 
          //      from our ctor and we want the set to happen.
          // 2.  If we do not have a Handle yet then we are 
          //        getting called by the infrastructure that
          //        creates a control.  
          // 3.  At design-time, the VS designer applies the
          //        Ambient color even if we explicitly set 
          //        our own color.  It is supposed to only apply
          //        the Ambient if we have not explictly set
          //        a color.
          // 4.  At runtime we must accept any color changes
          //        that are passed to us.


          // see if VS designer is screwing with us
          bool ignoreColorSet =
              _constructed
              && _handlesCreated == 0
              && RunningInDesigner;


          if (!ignoreColorSet)
          {
              base.BackColor = value;
              Repaint();
          }


      }
  }


  protected override void OnHandleCreated(EventArgs e)
  {
      _handlesCreated++;
      base.OnHandleCreated(e);         
  }

  private bool RunningInDesigner
  {
      get
      {
          // this control is mobile-only so if we are running on full
          //  windows we must be in design mode.  Note that this works
          //  even if we are not Sited yet, where as checking the 
          //  DesignMode property can't be done untl the control has
          //  a Site.
          return (System.Environment.OSVersion.Platform == PlatformID.Win32NT
              || System.Environment.OSVersion.Platform == PlatformID.Win32Windows);
      }
  }

}