XamarinDevDays/Demos/app-tasks/DevDaysTasks.Shared/Services/TodoItemManager.cs

using System;
using System.IO;
using System.Collections.ObjectModel;
using System.Diagnostics;
using System.Threading.Tasks;
using Microsoft.WindowsAzure.MobileServices;

using Microsoft.WindowsAzure.MobileServices.SQLiteStore;
using Microsoft.WindowsAzure.MobileServices.Sync;

namespace DevDaysTasks
{
    public partial class TodoItemManager
    {
        static TodoItemManager defaultInstance = new TodoItemManager();
        MobileServiceClient client;

        IMobileServiceSyncTable<TodoItem> todoTable;


        public async Task Initialize()
        {
            if (client?.SyncContext?.IsInitialized ?? false)
                return;


            client = new MobileServiceClient(Constants.ApplicationURL);

            var path = InitializeDatabase();
            var store = new MobileServiceSQLiteStore(path);
            store.DefineTable<TodoItem>();

            //Initializes the SyncContext using the default IMobileServiceSyncHandler.
            await client.SyncContext.InitializeAsync(store);

            todoTable = client.GetSyncTable<TodoItem>();

        }

        private string InitializeDatabase()
        {
#if __ANDROID__ || __IOS__
            CurrentPlatform.Init();
#endif
            SQLitePCL.Batteries.Init();

            var path = "localstore.db";

#if __ANDROID__
            path = Path.Combine(System.Environment.GetFolderPath(System.Environment.SpecialFolder.Personal), path);

            if (!File.Exists(path))
            {
                File.Create(path).Dispose();
            }
#endif

            return path;
        }

        public static TodoItemManager DefaultManager
        {
            get
            {
                return defaultInstance;
            }
            private set
            {
                defaultInstance = value;
            }
        }

        public MobileServiceClient CurrentClient
        {
            get { return client; }
        }

        public async Task<ObservableCollection<TodoItem>> GetTodoItemsAsync(bool syncItems = false)
        {
            try
            {
                await Initialize();

                if (syncItems)
                {
                    await SyncAsync();
                }

                var items = await todoTable
                    .Where(todoItem => !todoItem.Done)
                    .OrderBy(todoItem => todoItem.Name)
                    .ToEnumerableAsync();

                return new ObservableCollection<TodoItem>(items);
            }
            catch (MobileServiceInvalidOperationException msioe)
            {
                Debug.WriteLine(@"Invalid sync operation: {0}", msioe.Message);
                throw;
            }
            catch (Exception e)
            {
                Debug.WriteLine(@"Sync error: {0}", e.Message);
                throw;
            }
            return null;
        }

        public async Task SaveTaskAsync(TodoItem item)
        {
            await Initialize();

            if (item.Id == null)
            {
                await todoTable.InsertAsync(item);
            }
            else
            {
                await todoTable.UpdateAsync(item);
            }
            
        }


        public async Task SyncAsync()
        {
            await Initialize();

            ReadOnlyCollection<MobileServiceTableOperationError> syncErrors = null;

            try
            {
                await client.SyncContext.PushAsync();

                await todoTable.PullAsync(
                    //The first parameter is a query name that is used internally by the client SDK to implement incremental sync.
                    //Use a different query name for each unique query in your program
                    "allTodoItems",
                    todoTable.CreateQuery());
            }
            catch (MobileServicePushFailedException exc)
            {
                if (exc.PushResult != null)
                {
                    syncErrors = exc.PushResult.Errors;
                }
            }

            // Simple error/conflict handling. A real application would handle the various errors like network conditions,
            // server conflicts and others via the IMobileServiceSyncHandler.
            if (syncErrors != null)
            {
                foreach (var error in syncErrors)
                {
                    if (error.OperationKind == MobileServiceTableOperationKind.Update && error.Result != null)
                    {
                        //Update failed, reverting to server's copy.
                        await error.CancelAndUpdateItemAsync(error.Result);
                    }
                    else if(error.OperationKind != MobileServiceTableOperationKind.Update)
                    {
                        // Discard local change.
                        await error.CancelAndDiscardItemAsync();
                    }

                    Debug.WriteLine(@"Error executing sync operation. Item: {0} ({1}). Operation discarded.", error.TableName, error.Item["id"]);
                }
            }
        }
    }
}