ListGroups (Delphi)

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Description

This example requires a TListView control already on the form. Also, the GetImagesFromASCII routine together with the DigitsLetters variable, of type TImageList, need to be declared in the private part of the TForm1 class. This example shows how list groups can be customized and displayed in list view controls, using properties that are only available in Vista. Three list groups are created, for the digits, the small letters and the capital letters. The images for each list item are automatically generated and stored inside a TImageList component. The example also uses an additional routine, GetImagesFromASCII, that generates a series of images corresponding to the characters within some ASCII code interval.

Code

procedure TForm1.FormCreate(Sender: TObject);
var
  Group: TListGroup;
  ListItem: TListItem;
  Image: TBitmap;
  c: Char;
begin
  ShowMessage('a' + 'labala');

  { align the list view to the form }
  ListView1.Align := alClient;

  { center and stretch the form to fit the screen }
  Form1.Position := poScreenCenter;
  Form1.Height := 600;
  Form1.Width := 800;

  {
  change the view style of the list view
  such that the icons are displayed
  }
  ListView1.ViewStyle := vsIcon;

  { enable group view }
  ListView1.GroupView := True;

  { create a 32 by 32 image list }
  DigitsLetters := TImageList.CreateSize(32, 32);

  {
  generate the DigitsLetters image list with the digits,
  the small letters and the capital letters
  }
  GetImagesFromASCII('0', '9');
  GetImagesFromASCII('a', 'z');
  GetImagesFromASCII('A', 'Z');

  {
  add an empty image to the list
  used to emphasize the top and bottom descriptions
  of the digits group
  }
  Image := TBitmap.Create;
  Image.Height := 32;
  Image.Width := 32;
  DigitsLetters.Add(Image, nil);
  Image.Destroy;

  { create a title image for the small letters category }
  Image := TBitmap.Create;
  Image.Height := 32;
  Image.Width := 32;
  Image.Canvas.Brush.Color := clYellow;
  Image.Canvas.FloodFill(0, 0, clYellow, fsBorder);
  Image.Canvas.Font.Name := 'Times New Roman';
  Image.Canvas.Font.Size := 14;
  Image.Canvas.Font.Color := clRed;
  Image.Canvas.TextOut(3, 5, 'a..z');
  DigitsLetters.Add(Image, nil);
  Image.Destroy;

  { create a title image for the capital letters category }
  Image := TBitmap.Create;
  Image.Height := 32;
  Image.Width := 32;
  Image.Canvas.Brush.Color := clYellow;
  Image.Canvas.FloodFill(0, 0, clYellow, fsBorder);
  Image.Canvas.Font.Name := 'Times New Roman';
  Image.Canvas.Font.Size := 13;
  Image.Canvas.Font.Color := clRed;
  Image.Canvas.TextOut(2, 5, 'A..Z');
  DigitsLetters.Add(Image, nil);
  Image.Destroy;

  { associate the image list with the list view }
  ListView1.LargeImages := DigitsLetters;
  ListView1.GroupHeaderImages := DigitsLetters;

  { set up the digits group }
  Group := ListView1.Groups.Add;
  Group.State := [lgsNormal, lgsCollapsible];
  Group.Header := 'Digits';
  Group.HeaderAlign := taCenter;
  Group.Footer := 'End of the Digits category';
  Group.FooterAlign := taCenter;
  Group.Subtitle := 'The digits from 0 to 9';

  {
  use the empty image as the title image
  to emphasize the top and bottom descriptions
  }
  Group.TitleImage := DigitsLetters.Count - 3;

  { create the actual items in the digits group }
  for c := '0' to '9' do
  begin
    // add a new item to the list view
    ListItem := ListView1.Items.Add;

    // ...customize it
    ListItem.Caption := c + ' digit';
    ListItem.ImageIndex := Ord(c) - Ord('0');

    // ...and associate it with the digits group
    ListItem.GroupID := Group.GroupID;
  end;

  { set up the small letters group }
  Group := ListView1.Groups.Add;
  Group.State := [lgsNormal, lgsCollapsible];
  Group.Header := 'Small Letters';
  Group.HeaderAlign := taRightJustify;
  Group.Footer := 'End of the Small Letters category';
  Group.FooterAlign := taLeftJustify;
  Group.Subtitle := 'The small letters from ''a'' to ''z''';
  Group.TitleImage := DigitsLetters.Count - 2;

  { create the actual items in the small letters group }
  for c := 'a' to 'z' do
  begin
    // add a new item to the list view
    ListItem := ListView1.Items.Add;

    // ...customize it
    ListItem.Caption := 'letter ' + c;
    ListItem.ImageIndex := Ord(c) - Ord('a') + 10;

    // ...and associate it with the small letters group
    ListItem.GroupID := Group.GroupID;
  end;

  {
  to see how the NextGroupID property can be used,
  the following lines of code show how an item can be associated
  with a group ID, prior to creating the group
  }

  { create the actual items in the capital letters group }
  for c := 'A' to 'Z' do
  begin
    // add a new item to the list view
    ListItem := ListView1.Items.Add;

    // ...customize it
    ListItem.Caption := 'letter ' + c;
    ListItem.ImageIndex := Ord(c) - Ord('A') + 36;

    // ...and associate it with the capital letters group
    ListItem.GroupID := ListView1.Groups.NextGroupID;
  end;

  { set up the capital letters group }
  Group := ListView1.Groups.Add;
  Group.State := [lgsNormal, lgsCollapsible];
  Group.Header := 'Capital Letters';
  Group.HeaderAlign := taRightJustify;
  Group.Footer := 'End of the Capital Letters category';
  Group.FooterAlign := taLeftJustify;
  Group.Subtitle := 'The capital letters from ''A'' to ''Z''';
  Group.TitleImage := DigitsLetters.Count - 1;

end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  { remove the image list from memory }
  DigitsLetters.Destroy;
end;

{
Generates a series of images for the characters
starting with ASCII code First and ending with Last.
All images are added to the DigitsLetters variable.
procedure TForm1.GetImagesFromASCII(First, Last: Char);
var
  Image: TBitmap;
  c: Char;
begin
  for c := First to Last do
  begin
    Image := TBitmap.Create;
    Image.Height := 32;
    Image.Width := 32;
    Image.Canvas.Font.Name := 'Times New Roman';
    Image.Canvas.Font.Size := 22;
    Image.Canvas.TextOut((Image.Width - Image.Canvas.TextWidth(c)) div 2, 0, c);
    DigitsLetters.Add(Image, nil);
    Image.Destroy;
  end;
end;

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