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How to get a form handle/variable

Hi,

I have an MDI application. I guarantee that each MDIChild window can only have one copy open at a time. Within the code of the window, I need to do things or check things related to that window. For example, I need to check if the window is visible.

I would normally do this with...
if MyForm.Visible = true ...

Then question is: Is there an easy way to get 'MyForm'.
MyForm is a variable of type TMyForm. I know that when I look at the source code for the window, I have a variable declaration of
MyForm : TMyForm;

but this is not set to anything. I need to set it to a valid value. I can do this with this code...

// Create a handle to the Current Window
ThisWindow := nil;
with Application.MainForm do
for N := 0 to MDIChildCount - 1 do
if MDIChildren[N] is TMyForm then
ThisWindow := MDIChildren[N] as TMyFormF;

Isn't there an easier way to do this?

Please respond to gman@mics.net

heathprovost

var
N: Integer;
begin
with Application.MainForm do
for N := 0 to MDIChildCount - 1 do
begin
if not (MDIChildren[I] is TMyForm) then continue;
with TMyForm(MDIChildren[I]) do
begin
//do whatever
end;
end;
end;

This isnt much better, but it will run a little faster due to the removal of the second type check (the as). TypeCasting this way is much faster and you are already typechecking with the is statement.

heathprovost

Code correction -

var
N: Integer;
begin
with Application.MainForm do
for N := 0 to MDIChildCount - 1 do
begin
if not (MDIChildren[N] is TMyForm) then continue;
with TMyForm(MDIChildren[N]) do
begin
//do whatever
end;
end;
end;

viktornet

This would be even faster...

.....
ThisWindow := TMyFormF(MDIChildren[N]);
....

so that's not a solution also....

I don;t understand are you trying to see if a window is visible or if it is of the same type?!?!

-Viktor
-Ivanov

ASKER CERTIFIED SOLUTION

rwilson032697

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adeng

Have you try this :

1. After you make a new form in delphi IDE, goto menu : Project | Option : and remove MyForm from 'Auto-Create forms' List Box.

2. write this code :

procedure TMyForm.FormClose(Sender: TObject; var Action: TCloseAction);
begin
Action := caFree;
end;

procedure TMyForm.FormDestroy(Sender: TObject);
begin
MyForm := nil;
end;

3. Use this code to make MyForm visible and prevent multiple copy :

procedure TForm1.Button1Click(Sender: TObject);
begin
if not assigned(MyForm) then
MyForm := TMyForm.Create(Application);
MyForm.Show;
end;

Regards Adeng;