"Cannot make a visible Window modal"

Posted on 2009-04-13
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
  • 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.
ScreenConnect 6.0 Free Trial

At ScreenConnect, partner feedback doesn't fall on deaf ears. We collected partner suggestions off of their virtual wish list and transformed them into one game-changing release: ScreenConnect 6.0. Explore all of the extras and enhancements for yourself!


Accepted Solution

LucEngelen earned 60 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

ScreenConnect 6.0 Free Trial

Want empowering updates? You're in the right place! Discover new features in ScreenConnect 6.0, based on partner feedback, to keep you business operating smoothly and optimally (the way it should be). Explore all of the extras and enhancements for yourself!

Question has a verified solution.

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

Suggested Solutions

Title # Comments Views Activity
Using idhttp to login to instagram 2 89
how to center only a line in richedit? 4 57
Dev express lookupcombo 3 28
Firemonkey BASS_Init into a thread 17 8
In this tutorial I will show you how to use the Windows Speech API in Delphi. I will only cover basic functions such as text to speech and controlling the speed of the speech. SAPI Installation First you need to install the SAPI type library, th…
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…
This tutorial gives a high-level tour of the interface of Marketo (a marketing automation tool to help businesses track and engage prospective customers and drive them to purchase). You will see the main areas including Marketing Activities, Design …
This video shows how to quickly and easily add an email signature for all users on Exchange 2016. The resulting signature is applied on a server level by Exchange Online. The email signature template has been downloaded from: www.mail-signatures…

777 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