Xamarin Offline Sync with AzureMobileServices: Initial offline load incredibly slow - sqlite

Question

I'm successfully using Azure Mobile Services and Xamarin Forms to perform CRUD operations on an SQL DB hosted with Azure. The offline sync portion stores the data in an SQLite db on the phone. There's been a few bumps along the way to get it working as smoothly as we have it now, but this remains to be the last hurdle.
Problem
When the device has no connection (tested using Airplane mode on a variety of physical and emulated devices) - the first time it goes to access any of the offline data, it takes a very long time to return anything. This is the case if the data exists in the SQLite DB or not.
There is no exception thrown, or anything that I can see printed to the logs that indicates what the delay might be.
To give an idea, a PullAsync() on 20 rows might take 5 seconds while online, and that data is stored to the SQLite DB. After putting the device into offline mode, that same operation may take up to 60 seconds. These numbers are quite arbitrary, but the delay is noticeably much too long.
To add to this, this long load only occurs the very first time any Offline Sync method is called. After that, every method is near instant, as I would expect it to be - but why not the first time?
Expected Result
I would expect that because the data is stored on the device already, and no internet connection can be detected, it should return the data almost instantly.
Code
Sync Class
The GetPolicies() method is where the delay would occur.
This is a sample of one of the components. Every other component is the same format, but different data.
IMobileServiceSyncTable<policy_procedure> policyTable = SyncController.policyTable;
public async Task<List<policy_procedure>> GetPolicies(string companyId)
{
//SemaphoreSlim
await SyncController.dbOperation.WaitAsync();
try
{
await SyncController.Initialize();
await policyTable.PullAsync("policy_procedure", policyTable.Where(p => p.fk_company_id == companyId).Where(p=> p.signature!=null || p.signature!=""));
return await policyTable.ToListAsync();
}
catch (Exception ex)
{
//For some reason, when this method is called and the device is offline, it will fall into this catch block.
//I assume this is standard for offline sync, as it's trying to do a pull with no connection, causing it to fail.
//Through using breakpoints, the delay occurs even before it reaches this catch statement.
Console.WriteLine(ex);
return await policyTable.ToListAsync();
}
finally
{
SyncController.dbOperation.Release();
}
}
Sync Controller
public static SemaphoreSlim dbOperation = new SemaphoreSlim(1, 1);
public static MobileServiceClient client;
public static MobileServiceSQLiteStore store;
public static async Task Initialize()
{
try
{
//This line is not standard for Offline Sync.
//The plugin returns true or false for the devices current connectivity.
//It's my attempt to see if there is a connection, to eliminate the load time.
//This does immediately take it back to the try statement in GetPolicies
if (!CrossConnectivity.Current.IsConnected)
return;
if (client ? .SyncContext ? .IsInitialized ? ? false)
return;
client = new MobileServiceClient(AppSettings.azureUrl);
var path = "local.db"; //Normally uses company ID,
path = Path.Combine(MobileServiceClient.DefaultDatabasePath, path);
store = new MobileServiceSQLiteStore(path);
/************************/
#
region Table Definitions in local SQLite DB
//Define all the tables in the sqlite db
..
store.DefineTable < policy_procedure > ();
..#endregion
await client.SyncContext.InitializeAsync(store);
/************/
#
region Offline Sync Tables
..
policyTable = client.GetSyncTable < policy_procedure > ();
..#endregion
}
catch (Exception ex)
{
Console.WriteLine(ex)
}
}
What I've Tried
Well, I'm not too sure what's even causing this, so most of my attempts have been around forcing an exception before this wait time occurs, so that it can fall out of the GetPolicies try-catch, as the wait time appears to be on the PullAsync.
My most recent attempt at this is commented in the code above (SyncController), where I use James Montemagno's Connectivity Plugin to detect the phones network connectivity. (I've tested this separately, and this works correctly without delay.)

Answer 1

The short story is that you don't want to call PullAsync in your GetPolicies method if your device is offline. For example, you could do
try
{
await SyncController.Initialize();
if (CrossConnectivity.Current.IsConnected)
{
await policyTable.PullAsync("policy_procedure", policyTable.Where(p => p.fk_company_id == companyId).Where(p=> p.signature!=null || p.signature!=""));
}
return await policyTable.ToListAsync();
}
but you will also want to handle the case where this is the first time the app runs and so you don't have any records yet.