DateTimePicker - Set empty date

[Lainkes 0]

Hallo,

 

I want to assign a null value to a DateTimePicker when a checkbox is checked to tell the user that no date is needed.

So I assign the value NULL (found in some other internet topics) that will be converted to '30/12/1899'.

DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Date := Null;

I get an error message when this code is executed. See attached image.

 

To be complete, this is a DBDateTimePicker (Konopka) that is linked with my datasource.

So the meaning is to write directly a null value to the database when hitting the save button on my form.

 

Any idea what I'm doing wrong? 

Tips and tricks are welcome.

 

Greetings

 

Alain

Edited April 15 by Lainkes

[Uwe Raabe 2051]

The error message is pretty clear: Set the ShowCheckBox property of the DateTimePicker to True. 

 

You don't even have to set the Date property to NULL. It should be sufficient to uncheck the Checkbox or set the Checked property to False. That will write a NULL value to the data field instead of 30/12/1899. 

[Remy Lebeau 1375]

A DateTimePicker does not have a concept of a NULL date/time.  That is why it has an optional checkbox instead.  If you need the date/time value to be optional, then enable the check box, and if checked then use the date/time otherwise ignore it.  You can't assign a NULL date/time value, so just uncheck the box and set a default value if needed.

Edited April 16 by Remy Lebeau

[Lainkes 0]

Thanks for the info.

 

I'll try to make it more specific. I activated the ShowCheckBox property.

I have a DBCheckbox where the user can indicate if more info is needed. (check or uncheck)

See screenshot.

When the DBCheckbox is not checked, the datetimepicker component must be unvisible. And the date in the database must be set to a value that is not usable (like 30/12/1899).

If checked, the datetimepicker must be visible and the selected date must be saved. 

 

This is my code. 

 

procedure Tfrm_Page_Control.DBCheckBox44Click(Sender: TObject);
begin
  if TDBCheckBox(sender).Checked then
    begin
	  // write selected date to DB : OK
      DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Checked := True;
      DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Visible := True;
      DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Date := Now;
    end
  else
    begin
	  // write unusable date to DB : NOT OK 
      DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Checked := False;
      DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Visible := False;
    end;
end;

But when I uncheck the DBCheckbox, nothing changes in my DB. The last saved date is still available.

 

Thanks for your feedback and help. (or alternative solution).

[Stano 143]

I don't know the Konopka components. But:

1. In the second part of the code (else) you don't have a value for the date
2. Some components have the property "Allow null value"

[Lainkes 0]

I added a line with the lowest date possible, but it's not working.

I'm sure it's something stupid, but no idea what it is.

 

  if TDBCheckBox(sender).Checked then
    begin
          // write selected date to DB : OK
      DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Checked := True;
      DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Visible := True;
      DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Date := Now;
    end
  else
    begin
          // write unusable date to DB : NOT OK
      DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Date := strToDAte('30/12/1899');
      DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Checked := False;
      DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Visible := False;
    end;

 

[Uwe Raabe 2051]

It may be better to directly change the underlying data field instead of the control:

procedure Tfrm_Page_Control.DBCheckBox44Click(Sender: TObject);
begin
  DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.DataSource.Edit;
  if TDBCheckBox(sender).Checked then
    begin
      DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Field.AsDateTime := Now;
      DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Visible := True;
    end
  else
    begin
      DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Field.Clear;
      DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Visible := False;
    end;
end;

 

[Lainkes 0]

Thanks.

But now I get an error on the line 

DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Field.AsDateTime := Now;

when opening my form. 

[Uwe Raabe 2051]

That error implies that the underlying field is not existing, probably because the dataset is not open. I would expect that the line 

DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.DataSource.Edit;

I added to the code would cause an error first, but perhaps you just missed to copy that line into your code.

 

Anyway, besides checking for Field <> nil, the question is: Why would you want to set that value when the dataset is not open?

[Lainkes 0]

It seems that it was not in edit mode after all.

My mistake.

Edited April 16 by Lainkes

[Stano 143]

If an array of type Date has the option "null" in the DBTable so

DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Field.AsDateTime := 0;//  = strToDAte('30/12/1899')

You can set

DTP_STAT_HAND_GRIF_VOL_DOSSIER_OPVR_DATE.Field.Value := null;

[Remy Lebeau 1375]

8 hours ago, Lainkes said:

I have a DBCheckbox where the user can indicate if more info is needed. (check or uncheck)

See screenshot.

When the DBCheckbox is not checked, the datetimepicker component must be unvisible. And the date in the database must be set to a value that is not usable (like 30/12/1899).

If checked, the datetimepicker must be visible and the selected date must be saved. 

Then there is no point in enabling the CheckBox on the DateTimePicker itself.