public NewItemViewModel(
INavigationService navigationService,
ISafeMessagingCenter messagingCenter)
{
Item = new Item
{
Text = "Item name",
Description = "This is an item description."
};
SaveCommand = new SafeCommand(SaveAsync);
async Task SaveAsync()
{
messagingCenter.Send(this, "AddItem", Item);
await navigationService.PopAsync();
};
CancelCommand = new SafeCommand(CancelAsync);
async void CancelAsync() =>
await navigationService.PopAsync();
}
//ZM: Built-in dependency injection will resolve these services
public ItemsViewModel(
INavigationService navigationService,
IDataStore <Item> dataStore,
ISafeMessagingCenter messagingCenter)
{
Title = "Browse";
//ZM: Note how we can avoid async-void-lamdas (async () => ) by
// using SafeMessagingCenter and SafeCommand
// Unhandled exceptions are also caught and handled in app.cs
messagingCenter.Subscribe <NewItemViewModel, Item>(this, "AddItem", SaveNewItemAsync);
async Task SaveNewItemAsync(NewItemViewModel vm, Item item)
{
Items.Add(item);
await dataStore.AddItemAsync(item);
};
//ZM: Because we're extending ViewModelBase, the IsBusy property
// will be set to true while LoadItemsCommand is running.
// Alot of code is saved avoiding writing a t-c-f block with
// IsBusy condition
LoadItemsCommand = new SafeCommand(
LoadItemsAsync
, viewModel: this); //NB to use OneWay Binding in RefreshView
async Task LoadItemsAsync()
=> Items.ReplaceRange(await dataStore.GetItemsAsync(true));
//ZM: An example of page navigation
AddItemCommand = new SafeCommand(AddItemAsync);
async Task AddItemAsync() =>
await navigationService.PushAsync <NewItemViewModel>();
//ZM: Passing the data Item to the navigated ViewModel is easy
OnItemSelectedCommand = new SafeCommand <Item>(OnItemSelectedAsync);
async Task OnItemSelectedAsync(Item item) =>
await navigationService.PushAsync <ItemDetailViewModel, Item>(item);
}
public ComponentWithMessagingDependency(ISafeMessagingCenter messagingCenter)
{
_messagingCenter = messagingCenter;
_messagingCenter.Subscribe <ComponentWithMessagingDependency>(this, "test", dependency => Console.WriteLine("test"));
}
