public Form2() { InitializeComponent(); _testBLL = new TestBLL(); lbStu.DataSource = _testBLL.GetAllStudents().Select(x => x.StuNo).ToList(); lbStu.SelectedIndex = -1; lbRoom.DataSource = _testBLL.GetAllRooms().Select(x => x.Name).ToList(); lbRoom.SelectedIndex = -1; lbStuRoom.SelectedIndex = -1; }