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Nullable DateTimePicker

Pham Minh Tri

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4.84/5 (41 votes)

17 Nov 2003

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A standard DateTimePicker control that enables users to enter null value. The fact that it's not intensively modified ensures that it has no potential errors.

Sample Image - Nullable_DateTimePicker.jpg

Introduction

I had do a research on a DateTimePicker that could enter null value and found a lot of solutions to it. But one major problem with those is that they behave quite different from the standard ones and may have many potential bugs, as a result it took time to test before using in a real application. I just found another simple solution that could solve this problem with a little modification, so it could promise no bugs :-).

Solution

I have overridden the Value property to accept Null value as DateTime.MinValue, while maintaining the validation of MinValue and MaxValue of the standard control. That's all there's to it.

Because it's so simple, there's not much to say about it. Please refer to code for details.

License

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Written By

Pham Minh Tri

Vietnam

This member has not yet provided a Biography. Assume it's interesting and varied, and probably something to do with programming.

Comments and Discussions

Tom Fischer18-Jun-04 4:30

18-Jun-04 4:30

Appreciate your handiwork!

Could you have vb.net version

Tony Dong25-May-04 11:10

25-May-04 11:10

Hi there, I'd like to say that is very good idea, but could you convert it to vb.net version with the add function, may it help all people who need this one.

Nice control, but ...

SachaMartineau25-Feb-04 3:38

25-Feb-04 3:38

Did you try the case where u start with a null datetime ?

If you do that, you can't select anything anymore!

cheers ! Wink | ;)

Wink | ;)

Re: Nice control, but ...

Christian Graus25-May-04 12:40

Christian Graus

25-May-04 12:40

Surely anyone who can't convert C# to VB.NET should consider a career as a plumber ?

Christian

I have drunk the cool-aid and found it wan and bitter. - Chris Maunder

Re: Nice control, but ...

SteveHolland2-Feb-05 2:48

2-Feb-05 2:48

Here is a VB.Net version. In addition to allowing the date to be deleted (via F2 or Delete keys), the control's background color changes when it receives focus.

Public Class DateTimeControl
Inherits System.Windows.Forms.DateTimePicker
Private mdtmValue As Date = Now()
Private mstrCustomFormat As String
Private mdtpFormat As DateTimePickerFormat = DateTimePickerFormat.Long
Private mblnSettoNull As Boolean
Private mdtmMinValue As Date = DateTime.MinValue
Private mstrText As String
Private mBackBrush As SolidBrush

<Description("Accepts legitimate date value or DateTime.MinValue."), MergableProperty(False), Category("Behavior")> _
Public Shadows Property Value() As Date
'This property definition overrides the Value property for the DateTimePicker control
Get
'Return value stored in hidden variable
Return mdtmValue
End Get
Set(ByVal Value As Date)
'Set the hidden variable mdtValue
If mblnSettoNull = True Or Value = DateTime.MinValue Then
mblnSettoNull = False
mdtmValue = DateTime.MinValue
Else
mdtmValue = Value
MyBase.Value = mdtmValue
End If
End Set
End Property
<Description("Accepts a legitimate date or time format string."), MergableProperty(False), Category("Behavior")> _
Public Shadows Property CustomFormat() As String
Get
Return mstrCustomFormat
End Get
Set(ByVal Value As String)
mstrCustomFormat = Value
MyBase.CustomFormat = mstrCustomFormat
End Set
End Property
<DefaultValue(1), Description("Accepts a legitimate format such as Long, Short, Time or Custom."), MergableProperty(False), Category("Behavior")> _
Public Shadows Property Format() As DateTimePickerFormat
Get
Return mdtpFormat
End Get
Set(ByVal Value As DateTimePickerFormat)
mdtpFormat = Value
MyBase.Format = mdtpFormat
End Set
End Property

Public Shadows Property BackColor() As Color
Get
Return MyBase.BackColor
End Get
Set(ByVal Value As Color)
If Not mBackBrush Is Nothing Then
mBackBrush.Dispose()
End If
MyBase.BackColor = Value
mBackBrush = New SolidBrush(Me.BackColor)
Me.Invalidate()
End Set
End Property
Protected Overrides Sub WndProc(ByRef m As Message)
Const WM_ERASEBKGND As Int32 = &H14
If m.Msg = WM_ERASEBKGND Then
Dim g As Graphics = Graphics.FromHdc(m.WParam)
If mBackBrush Is Nothing Then
mBackBrush = New SolidBrush(Me.BackColor)
End If
g.FillRectangle(mBackBrush, Me.ClientRectangle)
g.Dispose()
Else
MyBase.WndProc(m)
End If
End Sub
Protected Overrides Sub OnKeyDown(ByVal e As KeyEventArgs)
'Clear out when Delete of F2 is pressed
If e.KeyCode = Keys.Delete OrElse e.KeyCode = Keys.F2 Then
mblnSettoNull = True 'Flag to indicate null value desired
Me.Format = DateTimePickerFormat.Custom
Me.CustomFormat = " "
Me.Value = DateTime.MinValue
ElseIf e.KeyCode = Keys.Down OrElse e.KeyCode = Keys.Left OrElse e.KeyCode = Keys.Right OrElse e.KeyCode = Keys.Up Then
If IsNothing(Me.Tag) Then
Me.Format = DateTimePickerFormat.Custom
Me.CustomFormat = "MM/dd/yyyy"

Else
Me.Format = DateTimePickerFormat.Custom
Me.CustomFormat = "MM/dd/yyyy hh:mm tt"
End If

End If
End Sub

Protected Overrides Sub OnCloseUp(ByVal eventargs As System.EventArgs)
'This event fires when the user dismisses the graphical calendar
Me.Format = DateTimePickerFormat.Custom
If IsNothing(Me.Tag) Then
Me.CustomFormat = "MM/dd/yyyy"
Else
Me.CustomFormat = "MM/dd/yyyy hh:mm tt"
End If
Me.Value = MyBase.Value
End Sub

Protected Overrides Sub OnLeave(ByVal e As System.EventArgs)
Me.BackColor = System.Drawing.SystemColors.Window
End Sub

Protected Overrides Sub OnEnter(ByVal e As System.EventArgs)
Me.BackColor = System.Drawing.Color.LightSteelBlue
End Sub
End Class

Overrides value??

EntLover12-Jan-04 3:32

12-Jan-04 3:32

Hi, anyone knows how do I overrides the value property in the class? (im trying to translate the c# code)

I get a message saying that the property in the base class has not been declared as overridable so this won't work

vb.net

Public Overrides Property Value() As DateTime
Get

End Get
Set(ByVal Value As DateTime)

End Set
End Property

Could you please reply to
pietrud@hotmail.com

Thanks a bunch!

Re: Overrides value??

UDALO17-Feb-04 6:39

UDALO

17-Feb-04 6:39

It's not an override : you have to mask the original property (in C# it's done with the new keyword; in VB.NET, it is Shadows;
For instance, this piece of code does nothing, but it works Smile | :)

Smile | :)

:

Public Class MyDateTimePicker
Inherits DateTimePicker

Public Shadows Property Value() As DateTime
Get
Return MyBase.Value
End Get
Set(ByVal Value As DateTime)
Value = MyBase.Value
End Set
End Property
End Class

Add ShowUpDown property support

Sebastien Arcand2-Jan-04 17:11

Sebastien Arcand

2-Jan-04 17:11

You can add support to the ShowUpDown property usually used for Time Format:

protected override void OnMouseUp(MouseEventArgs e)
{
if(this.ShowUpDown)
{
if (bIsNull)
{
this.Format = oldFormat;
this.CustomFormat = oldCustomFormat;
this.Value = DateTime.Now;
bIsNull = false;
}
}

base.OnMouseUp(e);
}

Firing OnValueChanged

Sebastien Lorion26-Dec-03 15:38

Sebastien Lorion

26-Dec-03 15:38

Your solution is simple and elegant, but two corrections should be made I think :

1- use OnKeyUp instead of OnKeyDown, because the latter is fired up repeatedly until the user releases the key.

2- You should fire up OnValueChanged manually when setting value to DateTime.MinValue. Here is the modified code :

C#

public new DateTime Value 
{
	get 
	{
		if (bIsNull)
			return DateTime.MinValue;
		else
			return base.Value;
	}
	set 
	{
		if (value == DateTime.MinValue)
		{
			if (bIsNull == false) 
			{
				oldFormat = this.Format;
				oldCustomFormat = this.CustomFormat;
				bIsNull = true;
			}

			this.Format = DateTimePickerFormat.Custom;
			this.CustomFormat = " ";
			
			// fire up OnValueChanged manually
			base.OnValueChanged(new EventArgs());
		}
		else 
		{
			if (bIsNull) 
			{
				this.Format = oldFormat;
				this.CustomFormat = oldCustomFormat;
				bIsNull = false;
			}
			base.Value = value;
		}
	}
}

Sébastien

Intelligence shared is intelligence squared.

Homepage : http://www.slorion.webhop.org

Re: Firing OnValueChanged

Balaji Vishnumolakala4-Nov-04 4:07

Balaji Vishnumolakala

4-Nov-04 4:07

How can I set the cursor in the DateTimePicker control, which indicates focus on this control to user, after setting its value to null, and tabbing to it from other controls?

Selecting the control with Tab

Mortens_HUN7-Mar-07 0:47

7-Mar-07 0:47

Hi all! I want to select this control with tab, and I found a solution, but I think it not the best. If somebody have an idea, share it with me please.

Here is the solution:

public new DateTime Value
{
get
{
if (bIsNull)
return DateTime.MinValue;
else
return base.Value;
}
set
{
if (value == DateTime.MinValue)
{
if (bIsNull == false)
{
oldFormat = this.Format;
oldCustomFormat = this.CustomFormat;
bIsNull = true;
}

this.Format = DateTimePickerFormat.Custom;
//this.CustomFormat = this.Format.toString();
this.CustomFormat = "yyyy";
base.OnValueChanged(new EventArgs());
}
else
{
if (bIsNull)
{
this.Format = oldFormat;
this.CustomFormat = oldCustomFormat;
bIsNull = false;
}
base.Value = value;
}
}
}

kvc13-Dec-03 3:47

13-Dec-03 3:47

Hi,

I want to use this code in vb. I created a class and converted from C to VB. I am not sure how to use the control. When I reference the namespace.datetimepicker inside my form, it blows up trying to wrtie the control. I do not see the control on my toolbox. I am clueless here how to implement this.

Thanks.

kvc12-Dec-03 8:10

12-Dec-03 8:10

I'm sorry I don't do this override stuff. How do I implement this code? Do I have to create a class? Can I add code to the existing datetimepicker? What do I do?

Re: implementation

Pham Minh Tri16-Dec-03 19:34

16-Dec-03 19:34

Just drag standard DateTimePicker control onto the form, then go to Code view and change its type to our extension class.

Cheers.

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