System.MissingFieldException using Dropbox.Api 4.3.1 on Xamarin.iOS

[robertmiles3]

I'm attempting a test file upload using...

using (var client = new DropboxClient("MY_GENERATED_ACCESS_TOKEN"))
using (var stream = new MemoryStream(Encoding.UTF8.GetBytes("some text")))
{
    var updated = await client.Files.UploadAsync(
        path: $"/Backup-{DateTime.Now.ToString("yyyy-MM-dd-HH.mm.ss.fff")}.json",
        mode: WriteMode.Overwrite.Instance,
        autorename: false,
        clientModified: null,
        mute: false,
        body: stream);
}

But, I'm getting a System.MissingFieldException...

System.MissingFieldException: Field 'Dropbox.Api.DropboxRequestHandler/<Dropbox.Api.Stone.ITransport.SendUploadRequestAsync>d__d`3<TRequest_REF, TResponse_REF, TError_REF>.<>4__this' not found.
  at Dropbox.Api.Files.Routes.FilesUserRoutes.UploadAsync (Dropbox.Api.Files.CommitInfo commitInfo, System.IO.Stream body) [0x00006] in <4ef505fca4004e3fa64095111cf70e73>:0 
  at Dropbox.Api.Files.Routes.FilesUserRoutes.UploadAsync (System.String path, Dropbox.Api.Files.WriteMode mode, System.Boolean autorename, System.Nullable`1[T] clientModified, System.Boolean mute, System.IO.Stream body) [0x0000d] in <4ef505fca4004e3fa64095111cf70e73>:0 
  at yomomma.Services.DataService+<BackupAsync>d__3.MoveNext () [0x0005a] in /Users/yomomma/Dropbox/dev/yomomma/yomomma.Shared/Services/DataService.cs:111 

I'm using a "Generated Access Token" that I've created on my developer portal. Any ideas as to what is going on here? It's not a helpful error message at all.

[Greg-DB]

Did you install the Dropbox.Api package? That's not built for Xamarin, but there is a third party version meant for Xamarin: Xamarin.Dropbox.Api. That's made by a third party, so we can't officially support or endorse it, but it may work for you.

[robertmiles3]

Tried both, same error on both.

[Greg-DB]

Thanks for confirming that. I just tried this code using v4.3.1 of the SDK in Visual Studio (not Xamarin), and it worked there. That being the case it seems the issue is specific to Xamarin, so I'm afraid I can't offer a solution. I'll send this along as a request for official support for the SDK on Xamarin.

[robertmiles3 · Accepted solution]

I actually just got it working. I had to add the "Microsoft.Bcl.Async" package as well. I noticed some errors in the console saying that "Microsoft.Threading.Tasks" wasn't found. After I added this package, all is well.