private async void AddTopic_Click(object sender, RoutedEventArgs e)
{
if (check() == 1 || check() == 2)
{
return;
}
selectedClass.addTopic(topicBox.Text, mainTextBox.Text);
saveFile();
topicBox.Text = "";
mainTextBox.Text = "";
List <string> topics = selectedClass.Topics;
topicsList.Items.Clear();
foreach (string topic in topics)
{
ComboBoxItem topicDispaly = new ComboBoxItem();
topicDispaly.Content = topic;
topicsList.Items.Add(topicDispaly);
}
}