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Roger Graham
Guest
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 Posted: Sat Jul 05, 2003 3:34 pm Post subject: OldValue returns NewValue in TField OnValidate |
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I have validation in a TClientDataSet TField OnValidate. This checks that
we are not changing a date field from or to a unallowed date.
If there is an error, I want to change the field back to the old value. The
help says
For example, the following line replaces current pending changes with a
field's original value:
NewValue := OldValue;
However, in the OnValidate event OldValue returns the newly entered value,
so I cannot validate the original value in the field.
If I move the event handler to the OnChange, then OldValue does return the
original value in the field, but setting NewValue to OldValue causes an
Access Violation in unit DB.
TDataSet.SetStateFieldValue
Field.AsVariant := Value;
If I set TFieldValue to OldValue, the DBEdit does not update unless the user
presses the Esc key.
The field is a date field and the locale is UK, i.e. dd/mm/yyyy.
How do I validate a TField and reset its value if invalid?
--
Regards
Roger Graham
Designkey Ltd
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Jim Poe
Guest
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| Posted: Mon Jul 07, 2003 4:55 pm Post subject: Re: OldValue returns NewValue in TField OnValidate |
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Roger Graham wrote:
| Quote: |
How do I validate a TField and reset its value if invalid?
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Raise an exception or call Abort.
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Roger Graham
Guest
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| Posted: Mon Jul 07, 2003 8:15 pm Post subject: Re: OldValue returns NewValue in TField OnValidate |
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| Quote: | How do I validate a TField and reset its value if invalid?
Raise an exception or call Abort.
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Doesn't work, new invalid value stays in field.
Even curiouser, on Inserting a new record, the OldValue in OnChange returns
the value in the record active before the insert, not null as I would
expect.
Regards
Roger Graham
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Dave Rowntree
Guest
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| Posted: Mon Jul 07, 2003 9:35 pm Post subject: Re: OldValue returns NewValue in TField OnValidate |
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"Roger Graham" <rgraham (AT) designkey (DOT) co.uk> wrote:
| Quote: | I have validation in a TClientDataSet TField OnValidate. This checks that
we are not changing a date field from or to a unallowed date.
If there is an error, I want to change the field back to the old value. The
help says
For example, the following line replaces current pending changes with a
field's original value:
NewValue := OldValue;
However, in the OnValidate event OldValue returns the newly entered value,
so I cannot validate the original value in the field.
|
OldValue is not available in the TField.OnValidate event.
| Quote: | If I move the event handler to the OnChange, then OldValue does return the
original value in the field, but setting NewValue to OldValue causes an
Access Violation in unit DB.
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In TField.OnChange you could put:
if Sender.Value <> Sender.OldValue then
Sender.Value := Sender.OldValue;
| Quote: | How do I validate a TField and reset its value if invalid?
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To access Sender.OldValue in a TField.OnValidate event you could use:
procedure TForm1.ClientDataSet1DetailsValidate(Sender: TField);
var
cdsClone: TClientDataSet;
begin
cdsClone := TClientDataSet.Create(nil);
try
cdsClone.CloneCursor((Sender.DataSet as TClientDataSet), False);
cdsClone.FieldByName(Sender.FieldName).Value; // returns
Sender.OldValue
Sender.Value; // returns the Sender proposed new value
finally
cdsClone.Free;
end;
end;
--
Dave Rowntree
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