private void GraterSubmitClick()
        {
            float mark;

            if (Single.TryParse(GetStudentsGraterThanInput, out mark))
            {
                var temp = myWebService.GetStudentsGraterThan(mark);
                GraterStudents.Clear();
                foreach (var item in temp)
                {
                    GraterStudents.Add(item);
                }
            }
        }
        private async void GraterSubmitClick()
        {
            float mark;

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

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