private void LowerSubmitClick()
        {
            float mark;

            if (Single.TryParse(GetStudentsLowerThanInput, out mark))
            {
                var temp = myWebService.GetStudentsLowerThan(mark);
                LowerStudents.Clear();
                foreach (var item in temp)
                {
                    LowerStudents.Add(item);
                }
            }
        }
        private async void LowerSubmitClick()
        {
            float mark;

            if (Single.TryParse(GetStudentsLowerThanInput, out mark))
            {
                var temp = await ServiceProvider.GetStudentLowerThan(mark);

                LowerStudents.Clear();
                foreach (var item in temp)
                {
                    LowerStudents.Add(item);
                }
            }
        }