Additional links and resources concerning nullable databinding:
I've been told and so far it has panned out, that you should have a layer of business objects in between your database datasource and your UI where you could just add an item as shahkalpesh recommends without concern of it going into the database.
Jez Humble has some information on binding nullable types at the bottom of this post and in comments Where it suggests binding to nullable types is doable if "you explicitly set the DataSourceUpdateMode to DataSourceUpdateMode.OnPropertyChanged".
Another article on databinding Nullable types: The Joy of Code - Databinding and Nullable types in WinForms.NET
Maybe this code for binding a nullable DateTimePicker could help you find addditional solutions for this or other nullable issues.
Also check out Dan Hannan for the source of where I came up with my extension method.
/// <summary>
/// From BReusable
/// </summary>
/// <param name="dtp"></param>
/// <param name="dataSource"></param>
/// <param name="valueMember"></param>
/// <remarks>With help from Dan Hanan at http://blogs.interknowlogy.com/danhanan/archive/2007/01/21/10847.aspx</remarks>
public static void BindNullableValue(this DateTimePicker dateTimePicker, BindingSource dataSource, String valueMember,bool showCheckBox)
{
var binding = new Binding("Value", dataSource, valueMember, true);
//OBJECT PROPERTY --> CONTROL VALUE
binding.Format += new ConvertEventHandler((sender, e) =>
{
Binding b = sender as Binding;
if (b != null)
{
DateTimePicker dtp = (binding.Control as DateTimePicker);
if (dtp != null)
{
if (e.Value == null)
{
dtp.ShowCheckBox = showCheckBox;
dtp.Checked = false;
// have to set e.Value to SOMETHING, since it's coming in as NULL
// if i set to DateTime.Today, and that's DIFFERENT than the control's current
// value, then it triggers a CHANGE to the value, which CHECKS the box (not ok)
// the trick - set e.Value to whatever value the control currently has.
// This does NOT cause a CHANGE, and the checkbox stays OFF.
e.Value = dtp.Value;
}
else
{
dtp.ShowCheckBox = showCheckBox;
dtp.Checked = true;
// leave e.Value unchanged - it's not null, so the DTP is fine with it.
}
}
}
});
// CONTROL VALUE --> OBJECT PROPERTY
binding.Parse += new ConvertEventHandler((sender, e) =>
{
// e.value is the formatted value coming from the control.
// we change it to be the value we want to stuff in the object.
Binding b = sender as Binding;
if (b != null)
{
DateTimePicker dtp = (b.Control as DateTimePicker);
if (dtp != null)
{
if (dtp.Checked == false)
{
dtp.ShowCheckBox = showCheckBox;
dtp.Checked = false;
e.Value = (Nullable<DateTime>)null;
}
else
{
DateTime val = Convert.ToDateTime(e.Value);
e.Value = val;
}
}
}
});
dateTimePicker.DataBindings.Add(binding);
}