Creating the ViewModel

Add a new ViewModel file into the ViewModel folder and name it as PostListViewModel.cs. It should inherit from the MvxViewModel class. Inject the implementation for the IPostService in the constructor method, like this:

private readonly IPostService _postService;
public PostListViewModel(IPostService postService)
{
_postService = postService;
}

The constructor method is the right way to use the IoC container to inject all its dependencies.

Then add a new property for Data-Binding. You can type mvxpropdp and press Tab to complete the input, as shown as below:

#region PostList;
private MvxObservableCollection<Post> _postList;
public MvxObservableCollection<Post> PostList
{
get => _postList;
set => SetProperty(ref _postList, value);
}
#endregion

Now we need to find a place to get the data when the page is loading. Find more details about the lifecycle of the ViewModel here: https://www.mvvmcross.com/documentation/fundamentals/viewmodel-lifecycle.

Let us focus on the Initialize method in the ViewModel, which is used to do some heavy loading operations, such as loading data from the APIs. It returns a Task, which can be marked as async. Add an override to this method, like this:

public override async Task Initialize()
{
// Async initialization, YEY!
await base.Initialize();
var response = await _postService.GetPostList();
if (response.IsSuccess)
{
PostList = new MvxObservableCollection<Post>(response.Result);
}
else
{
// TODO; Show some error messages.
}
}

That is why I use a ResponseMessage class to encapsulate the result from the APIs. If there are any problems about the HTTP request, this encapsulation is able to make sure the UI layer can deal with the response result correctly because all exceptions and the unexpected values have been handled in the Service layer. If you got a result, which has a False value to the IsSuccess property, show a friendly message to users, rather than throwing an exception.

Then we need to navigate to the PostListViewModel from the FirstViewModel. Update the constructor of the FirstViewModel to inject the IMvxNavigationService, as shown below:

private readonly IGreetingService _greetingService;
private readonly IMvxNavigationService _navigationService;
public FirstViewModel(IGreetingService greetingService, IMvxNavigationService navigationService)
{
_greetingService = greetingService;
_navigationService = navigationService;
}

IMvxNavigationService is used to implement the navigation between views. I will describe more about it in the next section. Use the code snippet mvxcmda to create an async command in the FirstViewModel.cs to navigate to the PostListViewModel, like this:

#region NavToPostListAsyncCommand;
private IMvxAsyncCommand _navToPostListAsyncCommand;
public IMvxAsyncCommand NavToPostListAsyncCommand
{
get
{
_navToPostListAsyncCommand = _navToPostListAsyncCommand ?? new MvxAsyncCommand(NavToPostListAsync);
return _navToPostListAsyncCommand;
}
}
private async Task NavToPostListAsync()
{
// Implement your logic here.
await _navigationService.Navigate<PostListViewModel>();
}
#endregion