Hi,
I had some trouble with a piece of code which was not working (my bad), and I restored it successfully. This code uses Preferences from Xamarin Essentials, and as I thought the problem was with it, I updated it with NuGet in the whole solution.
But now my problem is fixed, and I still face an issue that I can't resolve... The code works because I made tests, but I am not able to retrieve preferences at startup. Yet, preferences are correctly set at runtime, I checked its value in the app !
So, is it a known issue with Preferences ? It does not work in debug mode, neither release mode...
Precision : as I changed this piece of code to make it smarter and to preserve MVVM, I already tested Preferences and it worked very well even in debug mode... But as I updated it before being able to build again, I can't compare...
Thanks,
Galactose
(In case it's not a known issue, here is my code:
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.Linq;
using Xamarin.Essentials;
using CardioCALC.Models;
namespace CardioCALC.ViewModels
{
public sealed class FavoritesViewModel : ViewModelBase
{
/*
* SINGLETON :
* - Instance
* - Constructors to avoir other instance and be thread-safe
*/
public static FavoritesViewModel Instance { get; } = new FavoritesViewModel();
static FavoritesViewModel()
{ }
private FavoritesViewModel()
{
this.Favorites.CollectionChanged += OnFavoritesSaveChanges; // Autosave
}
/*
* CLASS : classic properties and methodes to be used in the singleton instance
* - separator : constant char for serialization/deserialization
* - favoritePreferenceKey : constant string to be used as Key in Xamarin.Essentials.Preferences
* - Methods to Add/Remove/Toggle favorites (update list AND the score instance)
*/
private const char separator = ',';
private const string favoritePreferenceKey = "favorites";
public ObservableCollection<Score> Favorites { get; private set; } = new ObservableCollection<Score>();
public ObservableCollection<Score> Scores { get => ScoreListViewModel.Instance.Scores; }
public void ToggleFavorite(Score score)
{
if (score.IsFavorite) this.RemoveFavoriteAndUpdate(score);
else this.AddFavoriteAndUpdate(score);
}
public void AddFavoriteAndUpdate(Score score)
{
score.IsFavorite = true;
if (!this.Favorites.Contains(score)) this.Favorites.AddSorted(score);
}
public void RemoveFavoriteAndUpdate(Score favorite)
{
favorite.IsFavorite = false;
this.Favorites.Remove(favorite);
}
// Auto-save favorites list with event
private void OnFavoritesSaveChanges(object sender, NotifyCollectionChangedEventArgs e)
{
this.SaveFavorites();
}
/*
* Methods to Save/Load favorites from database/preferences(with serialization/deserialization)
*/
public void LoadSavedFavorites()
{
this.Favorites.Clear(); // Clear favorites (ie. to reload favorites after locale change in ScoreListViewModel)
string favorites = Preferences.Get(favoritePreferenceKey, "");
if (favorites == "") return;
foreach (Score favorite in this.Deserialize(favorites))
{
this.AddFavoriteAndUpdate(favorite);
}
}
public void SaveFavorites()
{
if (this.Favorites.Count > 0)
Preferences.Set(favoritePreferenceKey, this.Serialize());
else Preferences.Remove(favoritePreferenceKey);
}
// Serialize favorites list into string format
public string Serialize()
{
if (this.Favorites.Count < 1) return "";
string favorites = "";
foreach (Score favorite in this.Favorites)
{
favorites += $"{favorite.PageName}{separator}";
}
return favorites.TrimEnd(separator);
}
// Deserialize favorites list from string to restore Collection
public ObservableCollection<Score> Deserialize(string favorites)
{
ObservableCollection<Score> favoritesList = new ObservableCollection<Score>();
foreach(string favorite in favorites.Split(separator))
{
favoritesList.Add(this.Scores.FirstOrDefault(s => s.PageName == favorite)); // this.Scores contains all scores
}
return favoritesList;
}
}
}
