Monday, September 7, 2009

DataTimePicker databinding vs nullable DateTime

I just came across an interesting problem. You can't bind a nullable dateTime directly to a dateTimePicker. At least not easily. Here's an extension method that handles the heavy lifting.


/// <summary>
/// 
/// </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)
{
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 = true;
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 = true;
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 = true;
dtp.Checked = false;
e.Value = (Nullable<DateTime>) null;
}
else
{
DateTime val = Convert.ToDateTime(e.Value);
e.Value =val;
}
}
}
});
dateTimePicker.DataBindings.Add(binding);
 
}

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