Async and Await

I am working with some DLLs that I cannot change in this case it is the Microsoft Band SDK. I have wrapped all the uwp specific code in compiler directives for NetFX_CORE and I have all the appropriate references/capabilities in both the Assembly_csharp project and the windows holographic project. I have tried 3 different methods all achieving the same results.

1st method: async start with await keywords
2nd method: FunctionAsync().GetAwaiter().GetResult();
3rd method: Start => initialize Tasks, Update check if task is complete and if it is then process result

All three succeed on short running processes and fail on long running processes.

Example:

Code (CSharp):

1. _bands = await BandClientManager.Instance.GetBandsAsync(); //Retrieves list of devices
2. _bands = BandClientManager.Instance.GetBandsAsync().GetAwaiter().GetResult(); //Passes
3.  
4. _client = await BandClientManager.Instance.ConnectAsync(_bands[0]); //Fails with "A Method was called at an unexpected time"
5.  
6. _client = BandClientManager.Instance.ConnectAsync(_bands[0]).GetAwaiter().GetResult(); //Fails with "A Method was called at an unexpected time"

even method 3 which I figured would let the task keep running and just catch it when it is complete also faults.

I am looked and cant seem to find anyone else having this problem. I saw an app in the WS that gets around it but I cant seem to figure out how. Anyone have any suggestions?

 

All 3 methods should work. It is hard to tell without looking at your actual code. Can you share a mininum repro?

 

Here is a Vanilla attempt directly from the Microsoft Band SDK Docs. BTW Thanks I have spent several weeks off and on trying to solve this problem. I stripped out the try catch for simplicity.

Code (CSharp):

1. using UnityEngine;
2.  
3. #if NETFX_CORE
4. using System;
5. using System.Collections;
6. using System.Collections.Generic;
7. using System.Linq;
8. using System.Threading.Tasks;
9.  
10. //Imported from the Microsoft BAND SDK
11. using Microsoft.Band;
12. using System.Diagnostics;
13. #endif
14.  
15. public class BandManager : MonoBehaviour
16. {
17.  
18. #if NETFX_CORE
19.     private IBandInfo[] _bands;
20.     private IBandClient _client;
21. #endif
22.  
23.     #if NETFX_CORE
24.     // Use this for initialization
25.     async void Start ()
26.     {
27.         _bands = await BandClientManager.Instance.GetBandsAsync();
28.  
29.         var band = _bands.First();
30.         //Code Breaks after waiting at this line, Same code works in uwp XAML app.
31.         _client = await BandClientManager.Instance.ConnectAsync(band);
32.     }
33.     #endif
34.  
35.     // Update is called once per frame
36.     void Update ()
37.     {
38.    
39.     }
40. }

 

have you tried to check if band has a correct value?
the await on 27 returns control to the main thread which can do some things that break the execution of line 31
if would generally use _bands.FirstOrDefault() on 29 to make sure it won't crash if bands is empty...and then check for null before you invoke the connect....additionally if would also try to lock the _bands not to generate a race-condition occuring (depending on what you do with Start....)

and have you tried this already?

var bands = await BandClientManager.Instance.GetBandsAsync();
if (!bands.Any())
{
//apply some logic here when there is no band detected....
return;
}
_band = await BandClientManager.Instance.ConnectAsync(bands[0]);