public void InitializeCollections() { customersComboBox.DisplayMember = "dni"; customersComboBox.ValueMember = "dni"; customersComboBox.DataSource = businesscontrol.findAllCustomers(); customersComboBox.SelectedIndex = -1; pickUpOfficeComboBox.DisplayMember = "address"; pickUpOfficeComboBox.ValueMember = "Id"; pickUpOfficeComboBox.DataSource = businesscontrol.findAllBranchOffices(); pickUpOfficeComboBox.SelectedIndex = -1; returnOfficeComboBox.DisplayMember = "address"; returnOfficeComboBox.ValueMember = "Id"; returnOfficeComboBox.DataSource = businesscontrol.findAllBranchOffices(); returnOfficeComboBox.SelectedIndex = -1; categoryComboBox.DisplayMember = "name"; categoryComboBox.ValueMember = "Id"; categoryComboBox.DataSource = businesscontrol.findAllCategories(); categoryComboBox.SelectedIndex = -1; driversListCheckBox.Items.Clear(); ICollection <Person> persons = businesscontrol.findAllPersons(); if (persons != null) { foreach (Person p in persons) { driversListCheckBox.Items.Add(p.dni); } } }