How to Use Realm Effectively in a Xamarin.Forms App

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public class UserInfoDTO
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{
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    public Guid Id { get; set; }
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    public string Name { get; set; }
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    public UserInfo ToModel()
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    {
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        return new UserInfo
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        {
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            Id = Id,
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            Name = Name,
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        };
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    }
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    public static UserInfoDTO FromModel(UserInfo user)
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    {
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        return new UserInfoDTO
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        {
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            Id = user.Id,
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            Name = user.Name,
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        };
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    }
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}

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public static class RealmService
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{
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    public static Realm GetRealm() => Realm.GetInstance();
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}

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public static async Task RetrieveUsers()
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{
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    try
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    {
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        //Retrieve data from the API
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        var users = await RestAPIClient.GetAllUsers();
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        //Persist data in Realm
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        using var realm = RealmService.GetRealm();
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        realm.Write(() =>
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        {
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            realm.Add(users.Select(u => u.ToModel()), update: true);
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        });
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    }
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    catch (HttpRequestException) //Offline/Service is not reachable
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    {
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    }
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}

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public class UserInfo : RealmObject
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{
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    [PrimaryKey]
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    public Guid Id { get; set; }
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    public string Name { get; set; }
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}
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public class GroceryItem : EmbeddedObject
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{
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    public string Name { get; set; }
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    public bool Purchased { get; set; }
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}
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public class ShoppingList : RealmObject
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{
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    [PrimaryKey]
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    public Guid Id { get; set; } = Guid.NewGuid();
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    public string Name { get; set; }
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    public ISet<UserInfo> Owners { get; }
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    public IList<GroceryItem> Items { get; }
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}

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public class ShoppingListsCollectionViewModel : BaseViewModel
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{
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    private readonly Realm realm;
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    private bool loaded;
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    public ICommand AddListCommand { get; }
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    public ICommand OpenListCommand { get; }
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    public IEnumerable<ShoppingList> Lists { get; }
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    public ShoppingList SelectedList
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    {
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        get => null;
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        set
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        {
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            OpenListCommand.Execute(value);
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            OnPropertyChanged();
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        }
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    }
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    public ShoppingListsCollectionViewModel()
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    {
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        //1
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        realm = RealmService.GetRealm();
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        Lists = realm.All<ShoppingList>();
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        AddListCommand = new AsyncCommand(AddList);
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        OpenListCommand = new AsyncCommand<ShoppingList>(OpenList);
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    }
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    internal override async void OnAppearing()
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    {
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        base.OnAppearing();
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        IDisposable loadingIndicator = null;
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        try
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        {
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            //2
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            if (!loaded)
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            {
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                //Page is appearing for the first time, sync with service
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                //and retrieve users and shopping lists
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                loaded = true;
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                loadingIndicator = DialogService.ShowLoading();
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                await DataService.TrySync();
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                await DataService.RetrieveUsers();
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                await DataService.RetrieveShoppingLists();
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            }
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            else
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            {
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                DataService.FinishEditing();
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            }
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        }
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        catch
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        {
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            await DialogService.ShowAlert("Error", "Error while loading the page");
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        }
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        finally
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        {
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            loadingIndicator?.Dispose();
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        }
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    }
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    //3
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    private async Task AddList()
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    {
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        var newList = new ShoppingList();
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        newList.Owners.Add(DataService.CurrentUser);
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        realm.Write(() =>
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        {
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            return realm.Add(newList, true);
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        });
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        await OpenList(newList);
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    }
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    private async Task OpenList(ShoppingList list)
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    {
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        DataService.StartEditing(list.Id);
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        await NavigationService.NavigateTo(new ShoppingListViewModel(list));
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    }
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}

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<ContentPage.Content>
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    <!--A-->
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    <ListView ItemsSource="{Binding Lists}"
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                    SelectionMode="Single"
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                    SelectedItem="{Binding SelectedList, Mode=TwoWay}">
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        <ListView.ItemTemplate>
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            <DataTemplate>
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                <!--B-->
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                <TextCell Text="{Binding Name}" />
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            </DataTemplate>
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        </ListView.ItemTemplate>
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    </ListView>
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</ContentPage.Content>

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public class ShoppingListViewModel : BaseViewModel
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{
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    private readonly Realm realm;
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    public ShoppingList ShoppingList { get; }
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    public IEnumerable<GroceryItem> CheckedItems { get; }
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    public IEnumerable<GroceryItem> UncheckedItems { get; }
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    public ICommand DeleteItemCommand { get; }
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    public ICommand AddItemCommand { get; }
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    public ICommand DeleteCommand { get; }
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    public ShoppingListViewModel(ShoppingList list)
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    {
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        realm = RealmService.GetRealm();
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        ShoppingList = list;
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        //1
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        CheckedItems = ShoppingList.Items.AsRealmQueryable().Where(i => i.Purchased);
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        UncheckedItems = ShoppingList.Items.AsRealmQueryable().Where(i => !i.Purchased);
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        DeleteItemCommand = new Command<GroceryItem>(DeleteItem);
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        AddItemCommand = new Command(AddItem);
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        DeleteCommand = new AsyncCommand(Delete);
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    }
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    //2
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    private void AddItem()
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    {
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        realm.Write(() =>
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        {
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            ShoppingList.Items.Add(new GroceryItem());
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        });
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    }
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    private void DeleteItem(GroceryItem item)
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    {
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        realm.Write(() =>
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        {
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            ShoppingList.Items.Remove(item);
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        });
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    }
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    private async Task Delete()
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    {
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        var confirmDelete = await DialogService.ShowConfirm("Deletion",
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            "Are you sure you want to delete the shopping list?");
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        if (!confirmDelete)
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        {
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            return;
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        }
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        var listId = ShoppingList.Id;
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        realm.Write(() =>
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        {
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            realm.Remove(ShoppingList);
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        });
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        await NavigationService.GoBack();
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    }
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}

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<ContentPage.Content>
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    <ScrollView>
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        <!--A-->
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        <StackLayout Orientation="Vertical" Margin="20" Spacing="10">
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            <!--B-->
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            <Editor Text="{Binding ShoppingList.Name}" HorizontalOptions="Fill"
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                    Placeholder="Shopping List Name"/>
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            <!--C-->
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            <StackLayout BindableLayout.ItemsSource="{Binding UncheckedItems}">
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                <BindableLayout.ItemTemplate>
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                    <DataTemplate>
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                        <!--G-->
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                        <StackLayout Orientation="Horizontal">
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                            <!--H-->
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                            <CheckBox IsChecked="{Binding Purchased}" VerticalOptions="Center"  />
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                            <!--I-->
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                            <Entry Text="{Binding Name}"
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                                    Keyboard="Email"
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                                    HorizontalOptions="FillAndExpand"
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                                    VerticalOptions="Center"/>
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                            <!--J-->
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                            <Button Text="X" FontSize="Title"
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                                Command="{Binding Path=BindingContext.DeleteItemCommand, Source={x:Reference page}}"
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                                CommandParameter="{Binding .}"/>
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                        </StackLayout>
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                    </DataTemplate>
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                </BindableLayout.ItemTemplate>
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            </StackLayout>
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             <!--D-->
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            <Button Text="+ Add Item" Command="{Binding AddItemCommand}"/>
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             <!--E-->
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            <BoxView Color="Gray" HeightRequest="1"/>
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            <Label Text="{Binding CheckedItems.Count, StringFormat='{0} ticked'}"/>
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            <!--F-->
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            <StackLayout BindableLayout.ItemsSource="{Binding CheckedItems}">
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                <BindableLayout.ItemTemplate>
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                    <DataTemplate>
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                        <StackLayout Orientation="Horizontal">
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                            <CheckBox IsChecked="{Binding Purchased}" VerticalOptions="Center"  />
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                            <Label Text="{Binding Name}" TextDecorations="Strikethrough"
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                                    HorizontalOptions="FillAndExpand"
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                                    VerticalOptions="Center"/>
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                            <Button Text="X" FontSize="Title"
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                                Command="{Binding Path=BindingContext.DeleteItemCommand, Source={x:Reference page}}"
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                                CommandParameter="{Binding .}"/>
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                        </StackLayout>
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                    </DataTemplate>
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                </BindableLayout.ItemTemplate>
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            </StackLayout>
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        </StackLayout>
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    </ScrollView>
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</ContentPage.Content>

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public static void StartEditing(Guid listId)
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{
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    PreferencesManager.SetEditingListId(listId);
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}
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public static void FinishEditing()
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{
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    var editingListId = PreferencesManager.GetEditingListId();
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    if (editingListId == null)
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    {
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        return;
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    }
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    //1
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    PreferencesManager.RemoveEditingListId();
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    //2
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    PreferencesManager.AddReadyForSyncListId(editingListId.Value);
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    //3
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    Task.Run(TrySync);
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}
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public static async Task TrySync()
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{
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    //4
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    var readyForSyncListsId = PreferencesManager.GetReadyForSyncListsId();
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    //5
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    var editingListId = PreferencesManager.GetEditingListId();
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    foreach (var readyForSyncListId in readyForSyncListsId)
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    {
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        //6
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        if (readyForSyncListId == editingListId)  //The list is still being edited
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        {
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            continue;
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        }
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        //7
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        var updateSuccessful = await UpdateShoppingList(readyForSyncListId);
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        if (updateSuccessful)
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        {
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            //8
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            PreferencesManager.RemoveReadyForSyncListId(readyForSyncListId);
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        }
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    }
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}

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private async Task OpenList(ShoppingList list)
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{
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    DataService.StartEditing(list.Id);
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    await NavigationService.NavigateTo(new ShoppingListViewModel(list));
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}

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internal override async void OnAppearing()
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{
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    base.OnAppearing();
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        if (!loaded)
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        {
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            ....
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            await DataService.TrySync();
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            ....
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        }
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        else
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        {
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            DataService.FinishEditing();
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        }
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    }
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}