How to display a table in ShowMessage?

I am trying to display a table using ShowMessage that looks like this:

short            | Description for "short"
verylongtext     | Description for "verylongtext"

How do I get two correctly aligned columns like that in a simple message dialog?

I tried to align the columns using spaces, but the font of ShowMessage is variable. Then I tried to align them using tab characters, but I do not know how to calculate the proper tab count for each row.

Is there a reliable way to calculate the tab count?

PS: I would like to avoid writing a custom dialog for this purpose.

You could use a list view in a custom dialog box, as well.

My class supports the standard Windows icons (and sounds): information, warning, error, confirmation, none. Here is the icon-less version:

It is easy to use:

TTableDialog.ShowTable
  (
    Self,
    'Audio Properties',
    ['Duration', 'Samples per channel', 'Total data size', 'Channels', 'Bits per sample', 'Sample rate', 'Bitrate'],
    ['1 h 15 min 0 s', '216 000 000', '824 MB', '1', '32', '48 kHz', '1 536 kbit/sec'],
    mtInformation
  )

It supports DPI scaling (high DPI) and all Windows versions from Windows XP (it might work on Windows 2000 as well, I just haven't tested that) to Windows 10:

The table is a list view, so you get all its benefits, like a scrollbar, truncation ellipses, and tooltips:

You can also specify the dialog's size to make it fit the contents:

TTableDialog.ShowTable
  (
    Self,
    'Audio Properties',
    ['Duration', 'Samples per channel', 'Total data size', 'Channels', 'Bits per sample', 'Sample rate', 'Bitrate', 'Maximum fractional sample value'],
    ['1 h 15 min 0 s', '216 000 000', '824 MB', '1', '32', '48 kHz', '1 536 kbit/sec', '0.1'],
    mtInformation,
    360,
    240
  )

Of course, the OK button is both Default and Cancel, so you can dismiss the dialog with Enter or Escape.

Finally, pressing Ctrl+C will copy the table to clipboard.

Full source code:

uses
  ComCtrls, Math, Clipbrd;

type
  TTableDialog = class
  strict private
    type TFormData = class(TComponent)
    public
      ListView: TListView;
      IconKind: PWideChar;
      Icon: HICON;
      LIWSD: Boolean;
    end;
    class function Scale(X: Integer): Integer;
    class procedure FormShow(Sender: TObject);
    class procedure FormDestroy(Sender: TObject);
    class procedure FormPaint(Sender: TObject);
    class procedure FormKeyPress(Sender: TObject; var Key: Char);
    class procedure LVToClipboard(AListView: TListView);
  public
    class procedure ShowTable(AOwner: TCustomForm; const ACaption: string;
      const ANames, AValues: array of string;
      ADialogType: TMsgDlgType = mtInformation;
      const AWidth: Integer = 360; const AHeight: Integer = 200);
  end;

class procedure TTableDialog.FormShow(Sender: TObject);
var
  FormData: TFormData;
  ComCtl: HMODULE;
  LoadIconWithScaleDown: function(hinst: HINST; pszName: LPCWSTR; cx: Integer;
    cy: Integer; var phico: HICON): HResult; stdcall;
begin
  if not (Sender is TForm) then
    Exit;
  if not (TObject(TForm(Sender).Tag) is TFormData) then
    Exit;
  TForm(Sender).OnShow := nil;
  FormData := TFormData(TForm(Sender).Tag);
  if FormData.IconKind = nil then
    Exit;
  ComCtl := LoadLibrary('ComCtl32.dll');
  if ComCtl <> 0 then
  begin
    try
      LoadIconWithScaleDown := GetProcAddress(ComCtl, 'LoadIconWithScaleDown');
      if Assigned(LoadIconWithScaleDown) then
        FormData.LIWSD := Succeeded(LoadIconWithScaleDown(0, FormData.IconKind,
          Scale(32), Scale(32), FormData.Icon));
    finally
      FreeLibrary(ComCtl);
    end;
  end;
  if not FormData.LIWSD then
    FormData.Icon := LoadIcon(0, FormData.IconKind);
end;

class procedure TTableDialog.FormDestroy(Sender: TObject);
var
  FormData: TFormData;
begin
  if not (Sender is TForm) then
    Exit;
  if not (TObject(TForm(Sender).Tag) is TFormData) then
    Exit;
  FormData := TFormData(TForm(Sender).Tag);
  if (FormData.Icon <> 0) and FormData.LIWSD then
    DestroyIcon(FormData.Icon);
end;

class procedure TTableDialog.FormKeyPress(Sender: TObject; var Key: Char);
var
  FormData: TFormData;
begin
  if not (Sender is TForm) then
    Exit;
  if not (TObject(TForm(Sender).Tag) is TFormData) then
    Exit;
  FormData := TFormData(TForm(Sender).Tag);
  case Key of
    ^C:
      LVToClipboard(FormData.ListView);
  end;
end;

class procedure TTableDialog.FormPaint(Sender: TObject);
var
  FormData: TFormData;
  Frm: TForm;
  Y: Integer;
begin

  if not (Sender is TForm) then
    Exit;

  if not (TObject(TForm(Sender).Tag) is TFormData) then
    Exit;

  Frm := TForm(Sender);
  FormData := TFormData(TForm(Sender).Tag);

  Y := Frm.ClientHeight - Scale(25 + 8 + 8);

  Frm.Canvas.Brush.Color := clWhite;
  Frm.Canvas.FillRect(Rect(0, 0, Frm.ClientWidth, Y));

  Frm.Canvas.Pen.Color := $00DFDFDF;
  Frm.Canvas.MoveTo(0, Y);
  Frm.Canvas.LineTo(Frm.ClientWidth, Y);

  if FormData.Icon <> 0 then
    DrawIconEx(Frm.Canvas.Handle, Scale(8), Scale(8), FormData.Icon,
      Scale(32), Scale(32), 0, 0, DI_NORMAL);

end;

class procedure TTableDialog.LVToClipboard(AListView: TListView);

  function GetRow(AIndex: Integer): string;
  begin
    if InRange(AIndex, 0, AListView.Items.Count - 1) and (AListView.Items[AIndex].SubItems.Count = 1) then
      Result := AListView.Items[AIndex].Caption + #9 + AListView.Items[AIndex].SubItems[0]
    else
      Result := '';
  end;

var
  S: string;
  i: Integer;
begin
  if AListView = nil then
    Exit;
  S := GetRow(0);
  for i := 1 to AListView.Items.Count - 1 do
    S := S + sLineBreak + GetRow(i);
  Clipboard.AsText := S;
end;

class function TTableDialog.Scale(X: Integer): Integer;
begin
  Result := MulDiv(X, Screen.PixelsPerInch, 96);
end;

class procedure TTableDialog.ShowTable(AOwner: TCustomForm; const ACaption: string;
  const ANames, AValues: array of string;
  ADialogType: TMsgDlgType = mtInformation;
  const AWidth: Integer = 360; const AHeight: Integer = 200);
const
  Sounds: array[TMsgDlgType] of Integer =
    (MB_ICONWARNING, MB_ICONERROR, MB_ICONINFORMATION, MB_ICONQUESTION, 0);
  Icons: array[TMsgDlgType] of MakeIntResource =
    (IDI_WARNING, IDI_ERROR, IDI_INFORMATION, IDI_QUESTION, nil);
var
  dlg: TForm;
  lv: TListView;
  btn: TButton;
  i: Integer;
  snd: Integer;
begin

  if Length(ANames) <> Length(AValues) then
    raise Exception.Create('The lengths of the columns don''t match.');

  dlg := TForm.Create(AOwner);
  try

    dlg.BorderStyle := bsDialog;
    dlg.Caption := ACaption;
    dlg.Width := Scale(AWidth);
    dlg.Height := Scale(AHeight);
    dlg.Position := poOwnerFormCenter;
    dlg.Scaled := False;
    dlg.Font.Name := 'Segoe UI';
    dlg.Font.Size := 9;
    dlg.Tag := NativeInt(TFormData.Create(dlg));
    TFormData(dlg.Tag).IconKind := Icons[ADialogType];
    dlg.OnShow := FormShow;
    dlg.OnDestroy := FormDestroy;
    dlg.OnPaint := FormPaint;
    dlg.OnKeyPress := FormKeyPress;
    dlg.KeyPreview := True;

    btn := TButton.Create(dlg);
    btn.Parent := dlg;
    btn.Caption := 'OK';
    btn.Default := True;
    btn.Cancel := True;
    btn.ModalResult := mrOk;
    btn.Width:= Scale(75);
    btn.Height := Scale(25);
    btn.Left := dlg.ClientWidth - btn.Width - Scale(8);
    btn.Top := dlg.ClientHeight - btn.Height - Scale(8);

    lv := TListView.Create(dlg);
    TFormData(dlg.Tag).ListView := lv;
    lv.Parent := dlg;
    lv.DoubleBuffered := True;
    lv.ReadOnly := True;
    lv.BorderStyle := bsNone;
    lv.Left := Scale(8) + IfThen(Icons[ADialogType] <> nil, Scale(32 + 8));
    lv.Top := Scale(8);
    lv.Width := dlg.ClientWidth - Scale(16) - IfThen(Icons[ADialogType] <> nil, Scale(32 + 8));
    lv.Height := dlg.ClientHeight - Scale(16 + 8 + 4) - btn.Height;
    lv.ViewStyle := vsReport;
    lv.RowSelect := True;
    lv.ShowColumnHeaders := False;

    with lv.Columns.Add do
    begin
      Caption := 'Name';
      Width := Scale(150);
    end;
    with lv.Columns.Add do
    begin
      Caption := 'Value';
      Width := lv.ClientWidth - lv.Columns[0].Width -
        GetSystemMetricsForWindow(SM_CXVSCROLL, dlg.Handle) - scale(2);
    end;

    for i := 0 to High(ANames) do
      with lv.Items.Add do
      begin
        Caption := ANames[i];
        SubItems.Add(AValues[i]);
      end;

    snd := Sounds[ADialogType];
    if snd <> 0 then
      MessageBeep(snd);

    dlg.ShowModal;

  finally
    dlg.Free;
  end;

end;

Update: A new version supports custom text and buttons: