[Setup]
AppName=My Program
AppVersion=1.5
DefaultDirName={pf}\My Program
OutputDir=userdocs:Inno Setup Examples Output

[Components]
Name: "file1"; Description: "File 1"
Name: "file2"; Description: "File 2"
Name: "file3"; Description: "File 3"

[Code]
procedure ComponentsClickCheck(Sender: TObject);
var
  ListBox: TNewCheckListBox;
begin
  ListBox := TNewCheckListBox(Sender);
  if (ListBox.ItemIndex >= 0) and (ListBox.ItemIndex <= 1) then
    ListBox.Checked[2] := ListBox.Checked[0] or ListBox.Checked[1];
end;

procedure InitializeWizard;
begin
  WizardForm.ComponentsList.OnClickCheck := @ComponentsClickCheck;
end;