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Enquiring Mind · Guest

Hi,

I have a client dataset called cdsEmployee that contains data from the
EMPLOYEE table of the EMPLOYEE.GDB database. I have defined a form class
TFormEmployeeRecord that displays the fields of an individual record using
data-aware controls linked to cdsEmployee, but I have deleted the global
variable FormEmployeeRecord from the unit with the form's class, as I want
the form to be instantiated inside a procedure. I have included in the unit
2 global procedures called ShowEmployeeRecord and ShowNewEmployeeRecord
designed to be called from another form. These create an internal instance
of the TFormEmployeeRecord form, then show the form in modal mode. The
ShowNewEmployeeRecord is as follows:

procedure ShowNewEmployeeRecord;
var
FormEmployeeRecord: TFormEmployeeRecord;
begin
{if FormEmployeeRecord<>nil then
FreeAndNil(FormEmployeeRecord); }
FormEmployeeRecord:= TFormEmployeeRecord.Create(nil);
try
Datamodule1.cdsEmployee.DisableControls;
Datamodule1.cdsEmployee.Insert;
FormEmployeeRecord.ShowModal;
finally
FreeAndNil(FormEmployeeRecord);
end;
end;

The purpose of this procedure is to display an empty record in Insert mode.
However I have encountered the following problems:

1. The "if FormEmployeeRecord<>nil " statement (that is commented out ) does
not work as I would expect. Even though FormEmployeeRecord is declared as a
local variable of the procedure, and there is no global variable by the same
name, Delphi does not initialise the variable with a nil value, but with an
instantiated object. I guess that this has something to do with the
requirements of loading the objects properties from a dfm file.

2. Although the statement Datamodule1.cdsEmployee.Insert temporarily puts
the CDS cdsEmployee into the dsInsert state, and in so doing initialises the
new blank record by executing the OnNewRecord event handler assigned to
cdsEmployee, the state is changed at some point before the statement
FormEmployeeRecord.ShowModal is executed. Thus we end up seeing displayed
the record last focussed rather than a new blank record. Stepping through
the code using the debugger, it appears that because the CDS has a
calculated field, for some reason the event handler OnCalcFields is called,
and this changes the state from dsInsert to dsCalcFields. And what's worse,
it does not do this for just one record (the new blank record or the record
last focussed), but the calculated field is recalculated for every record in
the dataset.

It seems that once you start using many facilities of the client dataset
model, including several event handlers, the state of the CDS takes on 'a
mind of its own', and becomes very difficult to control! cdsEmployee also
has several other event handlers, including an AfterScroll event handler to
synchronise the cursor of a many-to-many detail dataset with that of
cdsEmployee. Some of these event handlers seem to switch the state of the
CDS. During debugging I inserted some MessageDlg or ShowMessage calls to
display the values of some variables, and these have the immediate effect of
switching the state of the CDS to Post.

All I wish to be able to do is to lock the state of the client dataset to
dsInsert until such time as I want to unlock it and allow the Delphi
frmework control it automatically. That's the reason for the inclusion of
the statement cdsEmployee.DisableControls. The form's OnShow event handler
calls cdsEmployee.EnableControls to re-establish the link between the
behaviour of the CDS and that of the data-aware controls.

Can anyone explain what is going on and how to avoid the undesired
behaviour?

TIA.

Enquiring Mind

Kees Vermeulen (Kever-IT) · Guest

Enquiring Mind schreef:

Enquiring Mind · Guest

"Kees Vermeulen (Kever-IT)" <info (AT) kever (DOT) com> wrote in message
news:461cd0a4$1 (AT) newsgroups (DOT) borland.com...

Thanks for your comments.