private void AddProject() { if (_repository.IsEmployeeHeadOfDepartment(_employee)) { CustomMessageBox.ShowError("The employee is a Head of Department. A Head of Department can't have projects assigned."); return; } var viewModel = new NewEmployeeProjectViewModel(_employee); if (_dialogService.ShowDialog(viewModel) == true) { _employee.AddProject(viewModel.ProjectInvolement); Notify(() => Projects); } }