Title: Automatically loading a form "on demand"
Question: How can I get my forms created automatically "on demand" (when they are referenced)?
Answer:
If you have programmed in Visual Basic, probably you know what we are
talking about: when you reference a property or a method of form, it
is automatically created if necessary. For example, the following code
will generate an exception in Delphi if Form2 was not previously
created:
Form2.Show;
However it would work perfectly well in Visual Basic (without the
semicolon, of course), and we can make it work it Delphi too with
this little trick:
unit Unit2;
interface
uses ...;
type
TForm2 = class(TForm)
...
end;
function Form2: TForm2;
var
// Form2: TForm2;
implementation
{$R *.DFM}
var
RealForm2: TForm2;
function Form2: TForm2;
begin
if RealForm2 nil then
Form2 := RealForm2
else
Application.CreateForm(TForm2, Result);
end;
procedure TForm2.FormCreate(Sender: TObject);
begin
RealForm2 := Self;
end;
procedure TForm2.FormDestroy(Sender: TObject);
begin
RealForm2 := nil;
end;
initialization
RealForm2 := nil;
end.
What we did was replacing the Form2 variable with a function with the
same name and type. This function uses a "hidden" variable (declared
in the implementation section) -RealForm2- to check if the form is
created or not (and in the latter case, it will create it
automatically). We set the value of this hidden variable in the
OnCreate and OnDestroy events of the form to the address of the form
or nil respectively.