Synchronize 5 ListBoxes together

Question

im working on a little Project right now and i want to synchronize 5 listBoxes scrolling together. The names of the listboxes are:

KidList
PointList
NoteList
CommentList
CommentListKid

How can i do it?

Answer 1

You could try the following technique.

First, add a private field

  private
    SyncBoxes: TArray<TListBox>;

to your form and initialise it when the form is created:

procedure TForm1.FormCreate(Sender: TObject);
begin
  SyncBoxes := [ListBox1, ListBox2, ListBox3, ListBox4];
end;

Then define the following interposer class:

type
  TListBox = class(Vcl.StdCtrls.TListBox)
  strict private
    procedure Sync;
  protected
    procedure WMVScroll(var Message: TWMVScroll); message WM_VSCROLL;
    procedure CNCommand(var Message: TWMCommand); message CN_COMMAND;
    procedure WMMouseWheel(var Message: TWMMouseWheel); message WM_MOUSEWHEEL;
  end;

implemented as

procedure TListBox.CNCommand(var Message: TWMCommand);
begin
  inherited;
  if Message.NotifyCode = LBN_SELCHANGE then
    Sync;
end;

procedure TListBox.Sync;
var
  LB: TListBox;
begin
  for LB in Form1.SyncBoxes do
    if LB <> Self then
      LB.TopIndex := Self.TopIndex;
end;

procedure TListBox.WMMouseWheel(var Message: TWMMouseWheel);
begin
  inherited;
  Sync;
end;

procedure TListBox.WMVScroll(var Message: TWMVScroll);
begin
  inherited;
  Sync;
end;

Of course, in a real app you would refactor this.

The result is possibly good enough:

The list box's scrolling animation makes synchronisation a little bit delayed, however.