Check if a Form is Open ?

well, you could try looking for it with the findWindow api, though I would think the answer would be to try & never instantiate it more then once.  When show it you could try something like:

if form1 = nil then
 form1 := TForm1.create(some_owner);
form1.show;

GL
Mike

This is how I do it and it basically is the same as edey's comment just different syntax

if not Assigined(form1) then
     form1 := TForm1.create(nil);

or

if not Assigined(form1) then
     form1 := TForm1.create(Owner_of_Form);

Have tried both, neither works. Form will not open at all.
Do I have to initialise form1 first (vwForm in my case).

My code below.

var sysUser: String;
    vwForm: TForm;
    rwAccess : String;
begin
  sysUser:=LowerCase(SysInfo.CurrentUser);
  case menuBar.SelectedIndex of
  0:begin
     rwAccess:=AccessType(sysUser,'BUILDUP');

     if rwAccess='RW' then begin
        if not Assigned(vwForm) then begin
          vwForm:=TFormBuildUp.Create(Self,[arWrite]);
          vwForm.Show;
        end;
     end;
  ... other code below.

When I track the vwForm variable I get the following

vwForm: ([csInheritable], True, False, $5C7DA4, [fsCreatedMDIChild])

All Other code works until I add the code re: Checking if Form is opened.

Any ideas ?

I got to hit the sack so I will check back on this thread after I get some sleep.

you could iterate through the mainforms-childforms,
and compare its classname like

function mainform.formexists : TForm;
begin
  result := nil;
  for i := 0 to mdichildcount - 1 do
    if mdichilds[i] is TFormBuildUp then
      result := forms[i];
end;

and you could it call like

aform := formexists;
if aform = nil then
  with TFormBuildUp.Create(self) do
     show
else
  aform.show;

(just from head, syntax errors possible)

meikl ;-)

oh, no mdichilds,
then use
formcount instead of mdichildcount,
forms[] instead of mdichilds[]

meikl ;-)

CrazyOne,

How Obvious ?

I need to get away from my pc every now and then, and relook at the code after a while.

The code I had worked, which is similar to Kretzschmar's code, but as I stated, it is not an MDI App.

The problem was that the Form was included in the Apps Autocreate method, which I moved, and now works OK, as CrazyOne suggested.


Thanks to all.

Hi,

Well Meikl, will this also work with a non MDI application ?

Pjelias,

Are you using the sample form I posted in the other question ? If so, add the following line to the template form :

unit ARSample;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;

type
  { The different types of Access Right }
  TAccessRight = ( arRead, arWrite, arAdd, arRemove );
  { Will be used to hold any combination of TAccessRight }
  TAccessRights = set of TAccessRight;

  TForm1 = class(TForm)
    btnEdit: TButton;
    btnPost: TButton;
    btnCancel: TButton;
    btnDelete: TButton;
    btnDuplicate: TButton;
    btnInsert: TButton;
    btnButton1: TButton;
    procedure btnButton1Click(Sender: TObject);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
  private
    FAccessRights: TAccessRights;
    procedure SetAccessRights(const Value: TAccessRights);
    { Private declarations }
  protected
    procedure DisableButtons;
  public
    { Public declarations }
    Constructor Create( AOwner : TComponent; ARights : TAccessRights ); reintroduce; overload;
    property AccessRights : TAccessRights read FAccessRights write SetAccessRights;
  end;

<B>  TAccessRightsFormClass = Class of TForm1;</B>

Where you should replace TForm1 with the Class of the form you are using.  Then in the main form put the unit in the interface uses clause ( the topmost one ) and remove it from the implementation uses clause.

Next create a new method in your main form it should look like this :

unit MainForm;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls, arSample;

type
  TForm2 = class(TForm)
    btnButton1: TButton;
    procedure btnButton1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    procedure ShowOrCreateForm( aFormClass : TAccessRightsFormClass; AccessRights : TAccessRights );
  end;

var
  Form2: TForm2;

implementation

{$R *.DFM}

procedure TForm2.btnButton1Click(Sender: TObject);
begin
  ShowOrCreateForm( TForm1, [ arRead, arWrite ] );
end;

{*****************************************************************************
  Name           : TForm2.ShowOrCreateForm
  Author         : Lesage Stefaan
  Arguments      : aFormClass   - The class of the form you are looking for
                   AccessRights - The Access rights which should be used to
                                  create a new form if it isn't found.
  Return Values  : None
  Exceptions     : None
  Description    : This method will loop over all forms in the application to
                   find a form of the given class.  If such a form is found, it
                   will be shown.  If none was found, one will be created with
                   the given access rights and shown.
  History        :

  Date         By                   Description
  ----         --                   -----------
  03/07/2001   Lesage Stefaan       Initial creation of the Procedure.
 *****************************************************************************}

procedure TForm2.ShowOrCreateForm(aFormClass: TAccessRightsFormClass; AccessRights : TAccessRights);
var
  lcv   : Integer;
  Found : Boolean;
  aForm : TForm;
begin
  { Initialise the Variable }
  Found := False;
  aForm := Nil;

  { Loop over all forms of the application }
  for lcv := 0 to Pred( screen.FormCount ) do
  begin
    { Check if the form is of the given class }
    if Screen.Forms[ lcv ] is aFormClass then
    begin
      { If so Show it }
      aForm := Screen.Forms[ lcv ];
      Found := True;
    end;
  end;

  { If a form of our formclass was not found, create it }
  if ( Not Found ) then
  begin
    aForm := aFormClass.Create( Self, AccessRights );
  end;

  if ( Assigned ( aForm ) ) then
  begin
    aForm.Show;
  end;
end;

end.

As you see I added a button to my form which calls the method I created.  You should simply pass the class of the form you are looking for and the access rights which should be used to create a new form if none was found.

Best regards,


Stefaan

Just a few seconds too late ;-)

Stefaan,

just got a message re: the code you posted, took a look, it looks a bit cleaner than what I have done.

Question - if I was to open say 4-5 Forms at the same time (may be possible), using the above method, would it matter If the same Form variable was used, while Forms remained open - aForm.


pjelias

Hi,

Well the method I have given doesn't use any form variable at all.  It will check if a given Form Class is found.  The only drawback is that you won't be able to have two instances of a TForm1, but I thought that was exactly what you wanted to have.

Best regards,


Stefaan

.

.

It's really easy to steal questions  :o)

Sorry for the previous comments...

Steal questions ? What do you mean by that ?

Best regards,


Stefaan

Buying a question without paying. I'm not going to make a habit of it, don't worry   :o)

And, did you find a good answer ?

On the question "Can I steal a question?": Yes!
On the question "Check if a Form is Open?": I didn't look  :o)