public SelectLocationViewModel(AppViewModel screen, IConfigurationService configurationService, IGeocodeService geocoder)
{
this.HostScreen = screen;
this.configurationService = configurationService;
this.geocoder = geocoder;
ExecuteSearch = ReactiveCommand.CreateFromTask <string, IEnumerable <Location> >(
async searchTerm => await geocoder.SearchForLocationsAsync(searchTerm)
);
this.SaveSelectedLocation = ReactiveCommand.CreateFromTask(async() =>
{
await configurationService.ChangeSavedLocationAsync(this.SelectedLocation);
//Attempt to re-load app
screen.LoadCommand.Execute().Subscribe();
}, this.WhenAny(vm => vm.SelectedLocation, location => location.GetValue() != null));
this.WhenAnyValue(x => x.SearchTerm)
.Throttle(TimeSpan.FromMilliseconds(500), RxApp.MainThreadScheduler)
.Select(x => x?.Trim())
.DistinctUntilChanged()
.Where(x => !string.IsNullOrWhiteSpace(x))
.InvokeCommand(ExecuteSearch);
this.ExecuteSearch.IsExecuting.ToProperty(this, x => x.IsSearching, out this.isSearching, false);
searchResults = ExecuteSearch.ToProperty(this, x => x.SearchResults, new List <Location>());
}
public MainViewModel()
{
ExecuteSearch = ReactiveCommand.CreateAsyncTask(_ => GetSearchResultsFromFlickr(SearchTerm));
/* Creating our UI declaratively
*
* The Properties in this ViewModel are related to each other in different
* ways - with other frameworks, it is difficult to describe each relation
* succinctly; the code to implement "The UI spinner spins while the search
* is live" usually ends up spread out over several event handlers.
*
* However, with RxUI, we can describe how properties are related in a very
* organized clear way. Let's describe the workflow of what the user does in
* this application, in the order they do it.
*/
// We're going to take a Property and turn it into an Observable here - this
// Observable will yield a value every time the Search term changes (which in
// the XAML, is connected to the TextBox).
//
// We're going to use the Throttle operator to ignore changes that
// happen too quickly, since we don't want to issue a search for each
// key pressed! We then pull the Value of the change, then filter
// out changes that are identical, as well as strings that are empty.
//
// Finally, we use RxUI's InvokeCommand operator, which takes the String
// and calls the Execute method on the ExecuteSearch Command, after
// making sure the Command can be executed via calling CanExecute.
this.WhenAnyValue(x => x.SearchTerm)
.Throttle(TimeSpan.FromMilliseconds(800))
.Select(x => x.Trim())
.DistinctUntilChanged()
.Where(x => !string.IsNullOrWhiteSpace(x))
.InvokeCommand(ExecuteSearch);
// How would we describe when to show the spinner in English? We
// might say something like, "The spinner's visibility is whether
// the search is running". RxUI lets us write these kinds of
// statements in code.
//
// ExecuteSearch has an IObservable<bool> called IsExecuting that
// fires every time the command changes execution state. We Select() that into
// a Visibility then we will use RxUI's
// ToProperty operator, which is a helper to create an
// ObservableAsPropertyHelper object.
_spinnerVisibility = ExecuteSearch.IsExecuting
.ToProperty(this, x => x.SpinnerVisibility, false);
// We subscribe to the "ThrownExceptions" property of our ReactiveCommand,
// where ReactiveUI pipes any exceptions that are thrown in
// "GetSearchResultsFromFlickr" into. See the "Error Handling" section
// for more information about this.
ExecuteSearch.ThrownExceptions.Subscribe(ex =>
{
/* Handle errors here */
});
// Here, we're going to actually describe what happens when the Command
// gets invoked - we're going to run the GetSearchResultsFromFlickr every
// time the Command is executed.
//
// The important bit here is the return value - an Observable. We're going
// to end up here with a Stream of FlickrPhoto Lists: every time someone
// calls Execute, we eventually end up with a new list which we then
// immediately put into the SearchResults property, that will then
// automatically fire INotifyPropertyChanged.
_searchResults = ExecuteSearch.ToProperty(this, x => x.SearchResults, new List <FlickrPhoto>());
}
