asked on

sharing TObjectlist between Forms / Classes

In my form 1 I create an ObjectList, Form 2 has a Property xObjectList : TObjectList read FObjectList write Fobjectlist, where FObjectList is a local varible of Form 2.

I have been thinking that it is not a good programming style to do something like

Form2. xObjectList := Form1.ObjectList;

Therefore I change Form2 :

now
FObjectList := TObjectList.create;

FObjectList.assign (Form1.ObjectList)

.....

in form1 I did something like :

.....

form2.Form2. xObjectList := Form1.ObjectList; // now with assign inside form 2

form2.ShowModal;

if (Form2.Modalresult = mr ok ) then
begin

Form1.ObjectList := Form2.ObjectList

end;

but the new version is creating an abstract error

q1) what is an abstract error ?

q2) any chance to see the root cause of the abstract error by checking map file or ...

q3) which solution is better in respect to a good programming style ???

--- need no code , just a good explanation ---- !!!!

Geert G

an abstract error occurs when calling a procedure which was declared as abstract

you need to override this procedure
you will have to overwrite the assign procedure

Ephraim Wangoya

Assign is not the best option here. You just need a reference to the first ObjectList which is the way you did it the first time.
Using and assign here will mean that you have to create new objects for the list and assign their properties as well from the source object list

Using the property is fine. You can set it immediately after creating the form
so say
Form2 := TForm2.Create(Application);
try
//assign it here
Form2.ObjectList := ObjectList;
.....

This way you don't need to reassign the objects back to Form1 after they are modified in Form2

A second way is to create a global procedure in Form2 that takes in the ObjectList as a parameter. This is even better since the ObjectList reference is now protected within Form2. You won't need a property

finction ShowForm2(AObjectList: TObjectList): Integer;

implementation

function ShowForm2(AObjectList: TObjectList): Integer;
var
F: TForm2;
begin
F := TForm2.Create(Application);
try
F.FObjectList := AObjectList;
Result := F.ShowModal;
finally
FreeAndNil(F);
end;
end;

SOLUTION

Geert G

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Geert G

bdlm ... can you create a little test sample which shows what you want ?

ASKER CERTIFIED SOLUTION

developmentguru

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