How to update/refresh observable collection? - xamarin

Question

My observable collection is not getting updated. Once user views post and goes back to his home page he needs to go to another page to refresh his home page to reflect his last seen article.
So far example user sees article Coffee, goes back to his HP and there is no article Coffee in the collection. Then he goes to his profile(or any other page) and then goes back to HP and there is updated collection with article coffee. I have I notifyproperty
HomePage
public ArticleBrowser()
{
InitializeComponent();
Load();
}
private async void Load()
{
BindingContext = new MyArticlesBrowserViewModel();
if (BindingContext is MyArticlesBrowserViewModel)
{
var context = new MyArticlesBrowserViewModel();
await context.LoadDataForBestSellers();
lastThreeArticlesCarouselView.ItemsSource = null;
lastThreeArticlesCarouselView.ItemsSource = context.LastThreeArticles;
bestSellersCarouselView.ItemsSource = context.ListOfBestSellers;
}
}
<local:ExtendedCarouselViewControl x:Name="lastThreeArticlesCarouselView"
Grid.Row ="1"
HeightRequest="250"
ShowIndicators="True"
Margin="0"
VerticalOptions="Start"
IndicatorsTintColor="{ DynamicResource TranslucidBlack }"
CurrentPageIndicatorTintColor="{ DynamicResource BaseTextColor }"
ItemsSource="{ Binding LastThreeArticles, Mode=TwoWay }">
<cv:CarouselViewControl.ItemTemplate>
<DataTemplate>
<local:AvatArticlesBrowserHeaderItemTemplate />
</DataTemplate>
</cv:CarouselViewControl.ItemTemplate>
</local:ExtendedCarouselViewControl>
ViewModel
private static List<Article> _lastOpenedArticles;
private static List<DownloadedArticle> _allDownloadedArticles;
private static List<Article> _lastSeenArticles;
public ObservableCollection<ArticleDetailData> LastThreeArticles { get; } = new ObservableCollection<ArticleDetailData>();
void ShowLastListened()
{
var downloadedArticles = LangUpDataSaverLoader.DeserializeAllOptimizationData();
if (_lastOpenedArticles != null && _lastOpenedArticles.Count > 0)
{
foreach (var article in _lastOpenedArticles.Take(3))
{
var filename = string.Format(SharedConstants.ArticleImageUrl, SharedConstants.ApiBaseUri, article.Id);
var newCell = new ArticleDetailData()
{
Author = article.Author,
Description = article.Description,
Body = article.Description,
Section = article.Category,
Id = article.Id,
Subtitle = article.Description,
Title = article.NameCz,
WhenDay = article.DateCreate.Day.ToString() + " / ",
WhenMonth = article.DateCreate.Month.ToString() + " / ",
WhenYear = article.DateCreate.Year.ToString(),
FullDate = article.DateCreate.ToLongDateString(),
NumberOfWords = article.NumberOfWords,
AmountOfGrammarDescription = article.AmountOfGrammarDescription,
ArticleLength = article.ArticleLength,
Price = article.Price,
IsSubmitted = article.IsSubmitted,
BestSellerRating = article.BestSellerRating,
};
if (downloadedArticles.DownloadedArticles.Any(m => m.Id == article.Id))
{
newCell.BackgroundImage = article.Id.ArticleImageFile();
}
newCell.BackgroundImage = filename;
LastThreeArticles.Add(newCell);
}
}
}
public async Task LoadDataForBestSellers()
{
var articlesApiResponse = await AVAT.App.ApiFactory.GetBestSellerArticlesAsync();
var allArticles = articlesApiResponse.Match(articles => articles.ToList(), _ => new List<Article>());
FillArticles(allArticles);
if (LangUpLoggedUser.LoggedIn || LangUpLoggedUser.LoggedOffline)
{
LastThreeArticles.Clear();
var lastOpenedArticle = LangUpDataSaverLoader.DeserializeLastLoadedArticle();
lastOpenedArticle.Reverse();
_lastOpenedArticles = lastOpenedArticle;
ShowLastListened();
}
else
{
var freeArticlesApiResponse = await AVAT.App.ApiFactory.GetAllFreeArticlesAsync();
var allUserArticles = articlesApiResponse.Match(articles => articles.ToList(), _ => new List<Article>());
FillAnonymousArticles(allUserArticles);
}
}
I have tried Refresh Command but i was not getting any data back
public ICommand RefreshCommand { get; }
public MyArticlesBrowserViewModel()
: base()
{
RefreshCommand = new Command(async () => await ExecuteRefreshCommand());
}
async Task ExecuteRefreshCommand()
{
if (IsBusy) return;
IsBusy = true;
try
{
await LoadDataForBestSellers();
}
finally
{
IsBusy = false;
}
}

Answer 1

Solved with
protected override void OnAppearing()
{
base.OnAppearing();
var context = new MyArticlesBrowserViewModel();
lastThreeArticlesCarouselView.ItemsSource = null;
Task.Run(async () => await context.LoadDataForBestSellers()).Wait();
bestSellersCarouselView.ItemsSource = context.ListOfBestSellers;
lastThreeArticlesCarouselView.ItemsSource = context.LastThreeArticles;
}