private void AddExam_Button_Click(object sender, RoutedEventArgs e)
        {
            var            examName   = this.ExamName_TextBox.Text;
            var            examDate   = this.ExamDate_Calendar.SelectedDate;
            ExamController controller = new ExamController();

            try
            {
                Exams exam = new Exams()
                {
                    examName = examName, examTime = examDate
                };
                controller.AddExam(exam);

                ToLearnController toLearnController = new ToLearnController(exam.examName, 10);

                toLearnController.AddAndSaveLearnCycle();

                DataGridController dataGridController = new DataGridController(ExamGrid);
                dataGridController.SetDataSourceForExams();

                dataGridController.DataGrid = WhatToLearnToday_DataGrid;
                dataGridController.SetDataSourceForLearningDays();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
        private void DeleteExam_Button_Click(object sender, RoutedEventArgs e)
        {
            Exams examToDelete = new Exams();

            try
            {
                var itemToDelete = (Exams)ExamGrid.SelectedValue;
                examToDelete = itemToDelete;
            }
            catch (Exception)
            {
                MessageBox.Show("Prosze zaznaczyc obiekt");
            }
            try
            {
                ExamController controller = new ExamController();
                controller.DeleteExam(examToDelete.examId);
                try
                {
                    ToLearnController toLearnController = new ToLearnController(examToDelete.examName, 10);
                    toLearnController.DeleteLearningDayIfExamDeleteClicked();
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }

                DataGridController gridController = new DataGridController(ExamGrid);
                gridController.SetDataSourceForExams();
                gridController.DataGrid = WhatToLearnToday_DataGrid;
                gridController.SetDataSourceForLearningDays();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "Wystapil blad.");
            }
        }