private void AddProduct_Load(object sender, EventArgs e) { Task.Run(() => { Rest.GetCategoriesAsync().Wait(); if (InvokeRequired) { Invoke((Action)( () => { foreach (var s in Rest.categories) { CategoryListBox.Items.Add(s.name); } })); } else { foreach (var s in Rest.categories) { CategoryListBox.Items.Add(s.name); } } }); }