Scope of SQL query in multiple instances of a form - sql

Question

I have a form that I open multiple instances of. In there I use a SQL query to read some data from a database (Absolute Database in this case). I then fill out a few variables with data and also use the query for other operations during the lifetime of the form.
The problem is that when I open more than one instance of the form, the data change on the old forms to values from the last opened form.
I create the query in the form when it's opened so I thought that they wouldn't share the same data.
I don't use auto-created forms.
How can avoid this from happening?
** Edit - Added some code **
I create the form as follows:
procedure TfrmMain.OpenFormsFunction(Sender: TObject);
var
Resultater: TfrmregResultat;
begin
// Some code for checking if forms are already open
// Locate record in table to be used as paramdata in the query in the newly opened form
DataX.tStevneHead.Locate('StevneNummer;GrenType', VarArrayOf([StevneNummer, GrenType), []);
Resultater := TfrmRegResultat.Create(nil);
Resultater.Show; // OnClose action for the form is caFree
end;
Snip from the form's code
// decleared in implementation
Dato: TDate;
GrenType: string;
GrenRunder: integer;
MaxPoeng: integer;
procedure TfrmRegResultat.FormShow(Sender: TObject);
begin
//-- qStevneHead is a TABSQuery component on the form
//-- DataX is the name of my DataModule
with qStevneHead do
begin
Close;
SQL.Clear;
SQL.Text := 'SELECT * FROM StevneHead WHERE GrenType = :aGrenType AND StevneNummer = aStevneNummer';
ParamByName('aGrenType').AsString := DataX.tStevneHead.FieldByName('GrenType').Value;
ParamByName('aStevneNummer').AsString := DataX.tStevneHead.FieldByName('StevneNummer').Value;
Open;
end;
GrenRunder := qStevneHead.FieldByName('AntallRunder').Value;
Dato := qStevneHead.FieldByName('Dato').AsDateTime;
GrenType := qStevneHead.FieldByName('GrenType').Value;
MaxPoeng := qStevneHead.FieldByName('MaxPoeng').Value;
// More code to init stringgrid and other stuff on the form
end;

Answer 1

The problem seems to be that you're using global variables. Change them to be fields of the form and your problem should be solved. IOW, now you have
implementation
var
Dato: TDate;
GrenType: string;
GrenRunder: integer;
MaxPoeng: integer;
Change it to
type
TfrmRegResultat = class(...)
...
private
Dato: TDate;
GrenType: string;
GrenRunder: integer;
MaxPoeng: integer;
...
end;
If you need to access the values from some other part of the program (ie in the main form) then make them public propertyes or fields and access them via the currently active form variable.