Still celebrating National IT Professionals Day with 3 months of free Premium Membership. Use Code ITDAY17


"Cannot make a visible Window modal"

Posted on 2009-04-13
Medium Priority
Last Modified: 2012-05-06
I get the above error when running the code shown below. TfrmAddUser is NOT in the auto-create list. Its relevant properties are set as follows:

Visible: False
Enabled: True
FormStyle: fsNormal
WindowState: wsNormal

I am using Delphi 2006. I checked the existing Question:

... but nothing there seemed to make it work either. Any ideas, anyone?
procedure TfrmUserRoles.mAddUser;
  loAddUser: TfrmAddUser;
  lsUserID: string;
  loAddUser := TfrmAddUser.Create(nil, lsUserID);
    if (loAddUser.ShowModal = mrOk) then
      tvUsers.Items.Add(tvUsers.TopItem, lsUserID);

Open in new window

Question by:MartinC
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 4
  • 2

Expert Comment

ID: 24134223
Use this instead, and add the AddUser unit to whichever unit youre calling the dialog from

procedure TfrmUserRoles.mAddUser;
  lsUserID: string;
  if frmAddUser = nil then
    Application.CreateForm(TfrmAddUser, frmAddUser);

  if frmAddUser.ShowModal = mrOK then



Expert Comment

ID: 24134243
Oops, and frmAddUser := nil; after frmAddUser.Release, or you'll get access violations next time you call it.

Author Comment

ID: 24134333

Your method is an alternate way of calling a Modal form (and in fact one I have used before) but I was really hoping to find out why the code I wrote above - which conforms to methods used elsewhere in this app - might not work. The original code seems to be a reasonable way to do it - assign the created form to a local variable of type TfrmAddUser, and free it at the end after reading the returned lsUserID - but the error I get stymies me.
Concerto Cloud for Software Providers & ISVs

Can Concerto Cloud Services help you focus on evolving your application offerings, while delivering the best cloud experience to your customers? From DevOps to revenue models and customer support, the answer is yes!

Learn how Concerto can help you.


Accepted Solution

LucEngelen earned 240 total points
ID: 24134386
I dont know what your create constructor is doing, since you havent included it in your sample code.

Are you setting form.visible := true in there?  If so that is the reason for the issue.

You cannot call ShowModal once a window has had its visible state changed to true.

You may want to test this by just calling ;
loAddUser := TfrmAddUser.Create(nil);


Author Comment

ID: 24134449
And I wish I HAD included the constructor because then you would no doubt have spotted instantly what I left out:

  inherited create(AOwner);

I just spotted it then myself before reading your last comment, but thanks - and points - for your help anyway.

Expert Comment

ID: 24134571
It happens ;)  Its happened to me so many times I made it a habit to write inherited Create and inherited Destroy as soon as the begin and ends are in place, even if I wasnt working on those functions at the time.


Featured Post

What does it mean to be "Always On"?

Is your cloud always on? With an Always On cloud you won't have to worry about downtime for maintenance or software application code updates, ensuring that your bottom line isn't affected.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Have you ever had your Delphi form/application just hanging while waiting for data to load? This is the article to read if you want to learn some things about adding threads for data loading in the background. First, I'll setup a general applica…
Hello everybody This Article will show you how to validate number with TEdit control, What's the TEdit control? TEdit is a standard Windows edit control on a form, it allows to user to write, read and copy/paste single line of text. Usua…
This tutorial will teach you the special effect of super speed similar to the fictional character Wally West aka "The Flash" After Shake : All lightning effects with instructions : http://www.mediaf…
In response to a need for security and privacy, and to continue fostering an environment members can turn to for support, solutions, and education, Experts Exchange has created anonymous question capabilities. This new feature is available to our Pr…
Suggested Courses

722 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question