Adding custom properties to Silverlight controls

Question

Hello,

What is the best way for me to add my own properties to an existing Silverlight control? For example I would like to associate a custom class with the DataGrid and be able to set the properties of this custom class in Expression Blend?

Is this an easy thing to do?

Thanks,

AJ

Answer 1

By inheritance, it's pretty easy to do.

Here's for example a datagrid that triggers a validate event on enter keystroke.

namespace SLCommon
{
    public delegate void VaditateSelectionEventHandler(object sender, EventArgs e);

    /// <summary>
    /// Fires a validate event whenever the enter key or the left mouse button is pressed
    /// </summary>
    public class EventDatagrid : DataGrid
    {
        public event VaditateSelectionEventHandler Validate;

        public EventDatagrid()
            : base()
        {
            this.MouseLeftButtonUp += new MouseButtonEventHandler(OnMouseLeftButtonUp);
        }

        protected override void OnKeyDown(KeyEventArgs e)
        {
            if (e.Key != Key.Enter)
                base.OnKeyDown(e);
            else
            {
                e.Handled = true;
                Validate(this, e);
            }
        }

        protected void OnMouseLeftButtonUp(object sender, MouseButtonEventArgs e)
        {
           Validate(this, e);
        }
    }
}

XAML side:

<slc:EventDatagrid x:Name="toto" Validate="toto_Validate" 
                           AutoGenerateColumns="True"  IsReadOnly="True" Width="auto" MaxHeight="300">
</slc:EventDatagrid>

Note the Validate event handler.

Here after you can add a control myobj in a xaml file (be sure to declare the right xmlns: namespace on the top of your page) and set it's property.

Don't know about blend, but it sure works the same way.

Answer 2

Another option would be to use an attached behavior/property. It's the inheritance/composition argument - to extend functionality of class X, do you inherit from class X and extend it, or do you create class Y that contains class X?

Here's an example of someone adding PixelSnapping to SL via attached behavior: http://blogs.msdn.com/devdave/archive/2008/06/22/Using-an-Attached-DependencyProperty-to-Implement-Pixel-Snapping-as-an-Attached-Behavior.aspx