What is wrong with this object assignment?

[vfclists]

In the code below I am using the variable f as an abbreviation for a field named FDataModule. The idea is to check that the data module exists an display a related form. If the data module does not exist, it is created before.

I thought that by f:= FDataModule following by the Assigned procedure would work as I expected, f would not be nil iif FDataModule was already created. However in this case f is always nil and new forms are always opened.

What is wrong with the code?

Code: [Select]

procedure TdmCentral.actionExecute(Sender: TObject);
var
  f: TdmDateModule;
begin
  {
  f := FDataModule;
  if not Assigned(f) then
  begin
    f := TdmDataModule.Create(self);
  end;
  f.DisplayForm;
  }
  if not Assigned(FDataModule) then
  begin
    FDataModule := TdmDataModule.Create(self);
  end;
  FDataModule.DisplayForm;

end;

[Blaazen]

Strange.
Isn't there missing:

Code: [Select]

FDataModule := f;below the construction?
I mean that the TdmDateModule (in variable f) is created again and again but always lost (but not freed) when method ends.

[vfclists]

I see what you mean.

I thought that setting

Code: [Select]

f:= FDataModule and creating f would automatically assign FDataModule as well. In effect  Assigned(f) would be true if FDataModule was not nil to begin with.

Strange.
Isn't there missing:

Code: [Select]

FDataModule := f;below the construction?
I mean that the TdmDateModule (in variable f) is created again and again but always lost (but not freed) when method ends.

[User137]

Code: [Select]

  if not Assigned(FDataModule) then
  begin
    FDataModule := TdmDataModule.Create(self);
  end;
  FDataModule.DisplayForm;The code block looks fine. What else is happening, for instance have you debugged inside DisplayForm()? And how is FDataModule initialized? Can TdmDataModule.Create(self) take TdmCentral as parameter?

[vfclists]

The question is concerned with the part that is in comments. In any case the semantics were not what I thought they were, but Blaazen pointed out the error.

Code: [Select]

  if not Assigned(FDataModule) then
  begin
    FDataModule := TdmDataModule.Create(self);
  end;
  FDataModule.DisplayForm;The code block looks fine. What else is happening, for instance have you debugged inside DisplayForm()? And how is FDataModule initialized? Can TdmDataModule.Create(self) take TdmCentral as parameter?