How to alter a .NET DateTimePicker control to allow enter null values?
Here's an approach from this CodeProject article on creating a Nullable DateTimePicker.
I have overridden the
Value
property to acceptNull
value asDateTime.MinValue
, while maintaining the validation ofMinValue
andMaxValue
of the standard control.
Here's a version of the custom class component from the article
public class NullableDateTimePicker : System.Windows.Forms.DateTimePicker
{
private DateTimePickerFormat originalFormat = DateTimePickerFormat.Short;
private string originalCustomFormat;
private bool isNull;
public new DateTime Value
{
get => isNull ? DateTime.MinValue : base.Value;
set
{
// incoming value is set to min date
if (value == DateTime.MinValue)
{
// if set to min and not previously null, preserve original formatting
if (!isNull)
{
originalFormat = this.Format;
originalCustomFormat = this.CustomFormat;
isNull = true;
}
this.Format = DateTimePickerFormat.Custom;
this.CustomFormat = " ";
}
else // incoming value is real date
{
// if set to real date and previously null, restore original formatting
if (isNull)
{
this.Format = originalFormat;
this.CustomFormat = originalCustomFormat;
isNull = false;
}
base.Value = value;
}
}
}
protected override void OnCloseUp(EventArgs eventargs)
{
// on keyboard close, restore format
if (Control.MouseButtons == MouseButtons.None)
{
if (isNull)
{
this.Format = originalFormat;
this.CustomFormat = originalCustomFormat;
isNull = false;
}
}
base.OnCloseUp(eventargs);
}
protected override void OnKeyDown(KeyEventArgs e)
{
base.OnKeyDown(e);
// on delete key press, set to min value (null)
if (e.KeyCode == Keys.Delete)
{
this.Value = DateTime.MinValue;
}
}
}
You don't need to modify it to do this.
The DateTimePicker
in .net actually has a checkbox built-in.
Set the ShowCheckBox
property to true
.
Then you can use the Checked
property to see if the user has entered a value.
http://msdn.microsoft.com/en-us/library/system.windows.forms.datetimepicker.showcheckbox(VS.80).aspx