DataBinding Goodness

Submitted by Bevan on Mon, 27 Apr 2009 - 3:24pm

There's a lot of "goodness" buried in WinForms databinding that doesn't get to see the light of day. Here's one example I discovered just today ...

When you set up a Binding, one of the possible parameters is a boolean value for enable formatting:

    var binding 
        = new Binding(
            "EditValue",  // Name of the control property to bind
            aSubject,     // Data source
            aProperty,    // Path of property on the data source
            true,         // Is Formatting Enabled
            DataSourceUpdateMode.OnPropertyChanged);

The interesting thing is that turning enable formatting on does more than enable the Format and Parse events.

Check out the OnFormat() method of the Binding object, for example:

    protected virtual void OnFormat(ConvertEventArgs cevent)
    {
        if (onFormat != null)
        {
            onFormat(this, cevent);
        }
 
        if (!formattingEnabled
            && !(cevent.Value is DBNull)
            && cevent.DesiredType != null
            && !cevent.DesiredType.IsInstanceOfType(cevent.Value)
            && cevent.Value is IConvertible)
        {
            cevent.Value
                = Convert.ChangeType(
                    cevent.Value,
                    cevent.DesiredType,
                    CultureInfo.CurrentCulture);
        }
    }

If you turn on formatting, you also turn on automatic conversions between types that implement IConvertible. Amongst other things, this allows you to databind to nullable properties.

Neat.