public MaterialAndContractorsPackage SelectMaterial(IModalDialogService modalDialogService, IServiceFactory serviceFactory)
 {
     var viewModel = new ManageMaterialsViewModel(modalDialogService, serviceFactory);
       viewModel.DialogMode = DialogMode.Chose;
       ModalDialogHelper<ManageMaterials>.ShowDialog(viewModel);
       if (!viewModel.IsCanceled)
       {
     return viewModel.SelectableMaterial.SelectedItem;
       }
       return null;
 }
 public void ManageMaterials(IModalDialogService modalDialogService, IServiceFactory serviceFactory)
 {
     var viewModel = new ManageMaterialsViewModel(modalDialogService, serviceFactory);
       viewModel.DialogMode = DialogMode.Manage;
       ModalDialogHelper<ManageMaterials>.ShowDialog(viewModel);
 }