Strange behavior when a form is closed

unit uFrmList;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ExtCtrls, Vcl.ComCtrls, Vcl.Menus;

type
  TfrmList = class(TForm)
    lvForms: TListView;
    tmrList: TTimer;
    pmListview: TPopupMenu;
    mnuLvShow: TMenuItem;
    mnuLvFree: TMenuItem;
    procedure tmrListTimer(Sender: TObject);
    procedure mnuLvShowClick(Sender: TObject);
  private
    procedure ListForms;
  end;

var
  frmList: TfrmList;

implementation

{$R *.dfm}

procedure TfrmList.mnuLvShowClick(Sender: TObject);
var li: TListItem;
  frm, frx: TForm;
  I: Integer;
begin
  li := lvForms.Selected;
  if li <> nil then
  begin
    frm := nil;
    for I := 0 to Screen.FormCount-1 do
    begin
      frx := Screen.Forms[I];
      if (frx.Name = li.Caption) and (frx.Caption = li.SubItems[1]) then
      begin
        frm := frx;
        Break;
      end;
    end;
    if frm <> nil then
    begin
      if Sender = mnuLvShow then
      begin
        frm.Show;
        frm.BringToFront;
      end else // Sender = mnuLvFree
      begin
        if frm = Application.MainForm then
          Application.Terminate
        else
          frm.Free;
      end;
    end;
    ListForms;
  end;
end;

procedure TfrmList.tmrListTimer(Sender: TObject);
begin
  ListForms;
end;

procedure TfrmList.ListForms;
const
  states: Array[TWindowState] of string = ('Normal', 'Minimized', 'Maximized');
  Visibles: Array[Boolean] of string = ('Hidden', 'Visible');
var li: TListItem;
  I: Integer;
begin
  lvForms.Items.BeginUpdate;
  try
    lvForms.Items.Clear;
    for I := 0 to Screen.FormCount -1 do
    begin
      li := lvForms.Items.Add;
      li.Caption := Screen.Forms[I].Name;
      li.SubItems.Add(Screen.Forms[I].ClassName);
      li.SubItems.Add(Screen.Forms[I].Caption);
      li.SubItems.Add(States[Screen.Forms[I].WindowState]);
      li.SubItems.Add(Visibles[Screen.Forms[I].Visible]);
    end;
  finally
    lvForms.Items.EndUpdate;
  end;
end;

end.

Select all Open in new window

object frmList: TfrmList
  Left = 925
  Top = 352
  Caption = 'frmList'
  ClientHeight = 488
  ClientWidth = 566
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  FormStyle = fsStayOnTop
  OldCreateOrder = False
  Visible = True
  PixelsPerInch = 96
  TextHeight = 13
  object lvForms: TListView
    Left = 0
    Top = 0
    Width = 566
    Height = 488
    Align = alClient
    Columns = <
      item
        Caption = 'Name'
        Width = 80
      end
      item
        Caption = 'Class type'
        Width = 120
      end
      item
        Caption = 'Caption'
        Width = 120
      end
      item
        Caption = 'State'
        Width = 100
      end
      item
        Caption = 'Visible'
      end>
    PopupMenu = pmListview
    TabOrder = 0
    ViewStyle = vsReport
    ExplicitWidth = 404
  end
  object tmrList: TTimer
    Interval = 5000
    OnTimer = tmrListTimer
    Left = 48
    Top = 72
  end
  object pmListview: TPopupMenu
    Left = 200
    Top = 248
    object mnuLvShow: TMenuItem
      Caption = 'Show form'
      OnClick = mnuLvShowClick
    end
    object mnuLvFree: TMenuItem
      Caption = 'Free form'
      OnClick = mnuLvShowClick
    end
  end
end

Select all Open in new window