Develop Reference

Unable to return a value from SignalR Client from a different method

I'm working on a Winforms app that executes SQL Procedures through a SignalR client. I'm relatively new to using SignalR and am still wrapping my head around it.
I start off by running my connection method to establish a connection with my SignalR service. I have two addresses configured ready for when I puslish but the DEV configuration leads to the SignalR service I am hosting locally.
Connection to SignalR (ConnectHub)
private async Task ConnectHub()
{
string hubAddress = "";
#if DEBUG
HubAddress = ConfigurationManager.AppSettings["HubAddress_DEV"];
#else
HubAddress = ConfigurationManager.AppSettings["HubAddress_PROD"];
#endif
if (string.IsNullOrEmpty(hubAddress))
{
MessageBox.Show("Hub Address is missing from configuration.");
}
ConnectionHandler.Client = new HubClient(hubAddress, "MyHub");
ConnectionHandler.Client.MyAlert += ConnectionHandler.ClientOnMyAlert;
ConnectionHandler.Client.ServerErrorEvent += ConnectionHandler.ClientOnServerErrorEvent;
await ConnectionHandler.Client.Connect(new List<string>() {
VehicleInfo.ThisVehicle.WarehouseCode,
VehicleInfo.ThisVehicle.VehicleName
});
}
My client is stored globally in my ConnectionHandler class where my event handlers are also kept. (I have breakpoints on these as I have not implemented them yet)
ConnectionHandler Class
public static class ConnectionHandler
{
public static HubClient Client { get; set; }
public static void ClientOnServerErrorEvent(string error)
{
throw new NotImplementedException(); //Currently not implemented
}
public static async Task ClientOnMyAlert(EnumMyAlertType alerttype, string message, Exception exception)
{
await Task.Yield(); //Currently not implemented
}
}
When I call the code to Invoke the procedure in my SignalR client, it returns a DataTable to me which is the intended result.
Call to SignalR
await ConnectHub();
DataTable dt = await ConnectionHandler.Client.Connection.InvokeCoreAsync<DataTable>(
"FetchStatuses",
new object[0]); //This call works as intended and returns a populated DataTable
StatusInfo = new CStatuses();
All the above code is currently done on the main form, however I wanted to move this call to SignalR into a constructor to try and tidy things up.
The problem comes when I try to move this call into another method, the program hangs as I don't think it has received the return value from SignalR, I have placed a breakpoint beneath it and it is not reached. A TryCatch reveals nothing as it hangs within the "Try" with no exception.
Calling from contructor
public CStatuses()
{
Statuses = new List<CStatus>();
var dataTable = ConnectionHandler.Client.Connection.InvokeCoreAsync<DataTable>("FetchStatuses",
new object[0])
.Result; //My program hangs on this line and proceeds no further
I am at a loss as to why it is doing this when I can get a value from the client from the form and when other members of my team have tried to do the same thing they can make a call to SignalR also from a different method.
Does anyone have any ideas as to how I can make this work?
I realize this has gotten quite long but if I can elaborate on things please let me know
FIXED CODE THANKS TO SOLUTION:
I have moved the code from my CStatuses constructor into a new async method within the same class and called it after initialization. This removes the need for .Result and appears to solve the problem for me.
public async Task PopulateStatuses()
{
var dataTable = await ConnectionHandler.Client.Connection.InvokeCoreAsync<DataTable>("FetchStatuses",
new object[0]);
Statuses = new List<CStatus>();
foreach (DataRow row in dataTable.Rows)
{
var status = new CStatus
{
StatusId = Common.Utility.GetInt16Value(row["StatusID"]),
StatusCode = Common.Utility.GetStringValue(row["StatusCode"]),
Description = Common.Utility.GetStringValue(row["Description"])
};
Statuses.Add(status);
}
}

You are running into a deadlock with the .Result call, I would suggest creating an async method in the CStatuses class and after you initialize your CStatuses class call the websocket for data.

Different response from bot emulator and chatbot in web

I have created a chatbot in web channel and direct line.
When i tested in bot emulator i get the right response and when i try to test the same intent in localhost ( webchat) i got different response.
I will show you and example :
call an agent
give me your customer number
( after custemer number was sended ) are you sure ?
if you click Yes ...the data are stored in database ( sql server )
If you do the save in localhost you get : You cancelled the form ( in fact i havent cancell any form
Here is the luisdialog here i call the form :
[LuisIntent("human")]
public async Task human(IDialogContext context, LuisResult result)
{
var form = new FormDialog<Human>(
new Human(),
Human.BuildForm,
FormOptions.PromptInStart,
result.Entities);
context.Call<Human>(form, LossFormCompleted)
}
private async Task LossFormCompleted(IDialogContext context,
IAwaitable<Human> result)
{
HumanCall form = null;
try
{
form = await result;
}
catch (OperationCanceledException)
{
}
if (form == null)
{
await context.PostAsync("You cancelled the form.");
}
else
{
//call the LossForm service to complete the form fill
var message = $"Your data are stored in database";
await context.PostAsync(message);
}
context.Wait(this.MessageReceived);
}
The form model is :
[Serializable]
public class Human
{
[Prompt("What is your contract number?")]
public string contract;
public static IForm<Human> BuildForm()
{
OnCompletionAsyncDelegate<HumanCall> wrapUpRequest = async (context, state) =>
{
using (BotModelDataContext BotDb = new BotModelDataContext())
{
tblBot bot = new tblBot();
bot = BotDb.tblBots.SingleOrDefault(q => q.Reference == state.contract);
if (bot != null)
{
using (bbbserviceSoapClient cws = new bbbserviceSoapClient())
{
viewc a= new viewc();
a.Lastname = bot.Lastname;
}
}
}
};
return new FormBuilder<Human>().Message
("can you send us some info ?")
.Field(nameof(contract))
.OnCompletion(wrapUpRequest)
.Confirm("Are you sure: Yes or No. ")
.Build();
}
}
}
Can someone help me where i'm wrong ? What can i do to retrieve the same response ? It's about timeout problem or what do you thing ?

I do a test based on the code that you provided and make slight modifications, and I find that if some exceptions occur in wrapUpRequest method, it would show "You cancelled the form" instead of the message "Your data are stored in database".
So I suspect that exceptions occurring in wrapUpRequest method (perhaps database query issue or request sent by bbbserviceSoapClient is timeout etc) when you do test via web chat, which causes the issue.
To troubleshoot the issue, you can try to implement/write custom log to detect if any exception occurs within wrapUpRequest method when you test via web chat.

uwp c# async method waiting data not completely loaded exception

I will try to tell my problem in as simple words as possible.
In my UWP app, I am loading the data async wise on my Mainpage.xaml.cs`
public MainPage()
{
this.InitializeComponent();
LoadVideoLibrary();
}
private async void LoadVideoLibrary()
{
FoldersData = new List<FolderData>();
var folders = (await Windows.Storage.StorageLibrary.GetLibraryAsync
(Windows.Storage.KnownLibraryId.Videos)).Folders;
foreach (var folder in folders)
{
var files = (await folder.GetFilesAsync(Windows.Storage.Search.CommonFileQuery.OrderByDate)).ToList();
FoldersData.Add(new FolderData { files = files, foldername = folder.DisplayName, folderid = folder.FolderRelativeId });
}
}
so this is the code where I am loading up a List of FolderData objects.
There in my other page Library.xaml.cs I am using that data to load up my gridview with binding data.
protected override void OnNavigatedTo(NavigationEventArgs e)
{
try
{
LoadLibraryMenuGrid();
}
catch { }
}
private async void LoadLibraryMenuGrid()
{
MenuGridItems = new ObservableCollection<MenuItemModel>();
var data = MainPage.FoldersData;
foreach (var folder in data)
{
var image = new BitmapImage();
if (folder.files.Count == 0)
{
image.UriSource = new Uri("ms-appx:///Assets/StoreLogo.png");
}
else
{
for (int i = 0; i < folder.files.Count; i++)
{
var thumb = (await folder.files[i].GetThumbnailAsync(Windows.Storage.FileProperties.ThumbnailMode.VideosView));
if (thumb != null) { await image.SetSourceAsync(thumb); break; }
}
}
MenuGridItems.Add(new MenuItemModel
{
numberofvideos = folder.files.Count.ToString(),
folder = folder.foldername,
folderid = folder.folderid,
image = image
});
}
GridHeader = "Library";
}
the problem I am facing is that when i launch my application, wait for a few seconds and then i navigate to my library page, all data loads up properly.
but when i try to navigate to library page instantly after launching the app, it gives an exception that
"collection was modified so it cannot be iterated"
I used the breakpoint and i came to know that if i give it a few seconds the List Folder Data is already loaded properly asyncornously, but when i dnt give it a few seconds, that async method is on half way of loading the data so it causes exception, how can i handle this async situation? thanks

What you need is a way to wait for data to arrive. How you fit that in with the rest of the application (e.g. MVVM or not) is a different story, and not important right now. Don't overcomplicate things. For example, you only need an ObservableCollection if you expect the data to change while the user it looking at it.
Anyway, you need to wait. So how do you wait for that data to arrive?
Use a static class that can be reached from everywhere. In there put a method to get your data. Make sure it returns a task that you cache for future calls. For example:
internal class Data { /* whatever */ }
internal static class DataLoader
{
private static Task<Data> loaderTask;
public static Task<Data> LoadDataAsync(bool refresh = false)
{
if (refresh || loaderTask == null)
{
loaderTask = LoadDataCoreAsync();
}
return loaderTask;
}
private static async Task<Data> LoadDataCoreAsync()
{
// your actual logic goes here
}
}
With this, you can start the download as soon as you start the application.
await DataLoader.LoadDataAsync();
When you need the data in that other screen, just call that method again. It will not download the data again (unless you set refresh is true), but will simply wait for the work that you started earlier to finish, if it is not finished yet.

I get that you don't have enough experience.There are multiple issues and no solution the way you are loading the data.
What you need is a Service that can give you ObservableCollection of FolderData. I think MVVM might be out of bounds at this instance unless you are willing to spend a few hours on it. Though MVVM will make things lot easier in this instance.
The main issue at hand is this
You are using foreach to iterate the folders and the FolderData list. Foreach cannot continue if the underlying collection changes.
Firstly you need to start using a for loop as opposed to foreach. 2ndly add a state which denotes whether loading has finished or not. Finally use observable data source. In my early days I used to create static properties in App.xaml.cs and I used to use them to share / observe other data.

Xamarin.Android using async method on background thread causes screen flash

So I'm trying to create a loading/splash screen for an app that I'm creating. Basically, if the user isn't authenticated, then they shouldn't be able to access the other parts of the app. Additionally, I'd like the app to attempt to sync the necessary database objects before it loads up the main activity.
The problem is that when I call the Authenticate() method and the InitLocalStoreAsync() methods, the screen flashes (almost like an activity reload, or like the app is doing something that I don't understand that's hiding the activity) while the methods are executing. I'd like that not to happen.
I'm very new to Android App Dev and even newer to Xamarin.
I'm using modified code that comes from the Azure Mobile Services tutorial on authentication etc.
Should I be somehow executing these methods using RunOnUiThread? If so, how do I await in conjunction with RunOnUiThread? Or should I be doing this in a completely different way?
I'm very lost. I've tried to search and find tutorials to follow, but I can't seem to find the answer. Here's the code so far:
protected override async void OnCreate (Bundle bundle)
{
base.OnCreate (bundle);
SetContentView (Resource.Layout.Activity_Splash);
// Create your application here
try{
CurrentPlatform.Init ();
// Create the Mobile Service Client instance, using the provided
// Mobile Service URL and key
client = new MobileServiceClient (applicationURL, applicationKey);
statusText = FindViewById<TextView> (Resource.Id.SplashStatusText);
ThreadPool.QueueUserWorkItem(x => Initialize());
}catch(Java.Net.MalformedURLException){
CreateAndShowDialog (new Exception ("There was an error creating the Mobile Service. Verify the URL"), "Error");
}catch(Exception e) {
CreateAndShowDialog (e, "Error");
}
}
private async void Initialize()
{
RunOnUiThread(() => statusText.Text = "Authenticating...");
await Authenticate();
RunOnUiThread (() => statusText.Text = "Syncing...");
await InitLocalStoreAsync();
MoveToMainActivity();
}
private async Task Authenticate()
{
try
{
user = await client.LoginAsync(this, MobileServiceAuthenticationProvider.Google);
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
}
}
private async Task InitLocalStoreAsync()
{
// new code to initialize the SQLite store
string path = Path.Combine(System.Environment.GetFolderPath(System.Environment.SpecialFolder.Personal), localDbFilename);
if (!File.Exists(path))
{
File.Create(path).Dispose();
}
var store = new MobileServiceSQLiteStore(path);
store.DefineTable<ToDoItem>();
// Uses the default conflict handler, which fails on conflict
// To use a different conflict handler, pass a parameter to InitializeAsync. For more details, see http://go.microsoft.com/fwlink/?LinkId=521416
await client.SyncContext.InitializeAsync(store);
}
How do I restructure this so that I don't get any screen flashes?

If you want to run an asynchronous method you have to use the Task Factory:
RunOnUiThread(() => statusText.Text = "Loading.");
Task.Run(() => AsyncWork()).ContinueWith(result => RunOnUiThread(() => statusText.Text = "Done!"));
The screen flashes i think it could be 2 things, the app crashed and is trying to recover the last activity or your are trying to update elements on the UI thread and doing processing/work too, so it might be "stutter".

using EWS Managed API with ASP.NET MVC

I'm trying to create a web app which does many things but the one that I'm currently focused in is the inbox count. I want to use EWS StreamSubscription so that I can get notification for each event and returns the total count of items in the inbox. How can I use this in terms of MVC? I did find some code from Microsoft tutorial that I was gonna test, but I just couldn't figure how I could use it in MVC world i.e. What's the model going to be, if model is the count then how does it get notified every time an event occurs in Exchange Server, etc.
Here's the code I downloaded from Microsoft, but just couldn't understand how I can convert the count to json and push it to client as soon as a new change event occurs. NOTE: This code is unchanged, so it doesn't return count, yet.
using System;
using System.Linq;
using System.Net;
using System.Threading;
using Microsoft.Exchange.WebServices.Data;
namespace StreamingNotificationsSample
{
internal class Program
{
private static AutoResetEvent _Signal;
private static ExchangeService _ExchangeService;
private static string _SynchronizationState;
private static Thread _BackroundSyncThread;
private static StreamingSubscriptionConnection CreateStreamingSubscription(ExchangeService service,
StreamingSubscription subscription)
{
var connection = new StreamingSubscriptionConnection(service, 30);
connection.AddSubscription(subscription);
connection.OnNotificationEvent += OnNotificationEvent;
connection.OnSubscriptionError += OnSubscriptionError;
connection.OnDisconnect += OnDisconnect;
connection.Open();
return connection;
}
private static void SynchronizeChangesPeriodically()
{
while (true)
{
try
{
// Get all changes from the server and process them according to the business
// rules.
SynchronizeChanges(new FolderId(WellKnownFolderName.Inbox));
}
catch (Exception ex)
{
Console.WriteLine("Failed to synchronize items. Error: {0}", ex);
}
// Since the SyncFolderItems operation is a
// rather expensive operation, only do this every 10 minutes
Thread.Sleep(TimeSpan.FromMinutes(10));
}
}
public static void SynchronizeChanges(FolderId folderId)
{
bool moreChangesAvailable;
do
{
Console.WriteLine("Synchronizing changes...");
// Get all changes since the last call. The synchronization cookie is stored in the _SynchronizationState field.
// Only the the ids are requested. Additional properties should be fetched via GetItem calls.
var changes = _ExchangeService.SyncFolderItems(folderId, PropertySet.IdOnly, null, 512,
SyncFolderItemsScope.NormalItems, _SynchronizationState);
// Update the synchronization cookie
_SynchronizationState = changes.SyncState;
// Process all changes
foreach (var itemChange in changes)
{
// This example just prints the ChangeType and ItemId to the console
// LOB application would apply business rules to each item.
Console.Out.WriteLine("ChangeType = {0}", itemChange.ChangeType);
Console.Out.WriteLine("ChangeType = {0}", itemChange.ItemId);
}
// If more changes are available, issue additional SyncFolderItems requests.
moreChangesAvailable = changes.MoreChangesAvailable;
} while (moreChangesAvailable);
}
public static void Main(string[] args)
{
// Create new exchange service binding
// Important point: Specify Exchange 2010 with SP1 as the requested version.
_ExchangeService = new ExchangeService(ExchangeVersion.Exchange2010_SP1)
{
Credentials = new NetworkCredential("user", "password"),
Url = new Uri("URL to the Exchange Web Services")
};
// Process all items in the folder on a background-thread.
// A real-world LOB application would retrieve the last synchronization state first
// and write it to the _SynchronizationState field.
_BackroundSyncThread = new Thread(SynchronizeChangesPeriodically);
_BackroundSyncThread.Start();
// Create a new subscription
var subscription = _ExchangeService.SubscribeToStreamingNotifications(new FolderId[] {WellKnownFolderName.Inbox},
EventType.NewMail);
// Create new streaming notification conection
var connection = CreateStreamingSubscription(_ExchangeService, subscription);
Console.Out.WriteLine("Subscription created.");
_Signal = new AutoResetEvent(false);
// Wait for the application to exit
_Signal.WaitOne();
// Finally, unsubscribe from the Exchange server
subscription.Unsubscribe();
// Close the connection
connection.Close();
}
private static void OnDisconnect(object sender, SubscriptionErrorEventArgs args)
{
// Cast the sender as a StreamingSubscriptionConnection object.
var connection = (StreamingSubscriptionConnection) sender;
// Ask the user if they want to reconnect or close the subscription.
Console.WriteLine("The connection has been aborted; probably because it timed out.");
Console.WriteLine("Do you want to reconnect to the subscription? Y/N");
while (true)
{
var keyInfo = Console.ReadKey(true);
{
switch (keyInfo.Key)
{
case ConsoleKey.Y:
// Reconnect the connection
connection.Open();
Console.WriteLine("Connection has been reopened.");
break;
case ConsoleKey.N:
// Signal the main thread to exit.
Console.WriteLine("Terminating.");
_Signal.Set();
break;
}
}
}
}
private static void OnNotificationEvent(object sender, NotificationEventArgs args)
{
// Extract the item ids for all NewMail Events in the list.
var newMails = from e in args.Events.OfType<ItemEvent>()
where e.EventType == EventType.NewMail
select e.ItemId;
// Note: For the sake of simplicity, error handling is ommited here.
// Just assume everything went fine
var response = _ExchangeService.BindToItems(newMails,
new PropertySet(BasePropertySet.IdOnly, ItemSchema.DateTimeReceived,
ItemSchema.Subject));
var items = response.Select(itemResponse => itemResponse.Item);
foreach (var item in items)
{
Console.Out.WriteLine("A new mail has been created. Received on {0}", item.DateTimeReceived);
Console.Out.WriteLine("Subject: {0}", item.Subject);
}
}
private static void OnSubscriptionError(object sender, SubscriptionErrorEventArgs args)
{
// Handle error conditions.
var e = args.Exception;
Console.Out.WriteLine("The following error occured:");
Console.Out.WriteLine(e.ToString());
Console.Out.WriteLine();
}
}
}
I just want to understand the basic concept as in what can be model, and where can I use other functions.

Your problem is that you are confusing a service (EWS) with your applications model. They are two different things. Your model is entirely in your control, and you can do whatever you want with it. EWS is outside of your control, and is merely a service you call to get data.
In your controller, you call the EWS service and get the count. Then you populate your model with that count, then in your view, you render that model property. It's really that simple.
A web page has no state. It doesn't get notified when things change. You just reload the page and get whatever the current state is (ie, whatever the current count is).
In more advanced applications, like Single Page Apps, with Ajax, you might periodically query the service in the background. Or, you might have a special notification service that uses something like SignalR to notify your SPA of a change, but these concepts are far more advanced than you currently are. You should probably develop your app as a simple stateless app first, then improve it to add ajax functionality or what not once you have a better grasp of things.

That's a very broad question without a clear-cut answer. Your model could certainly have a "Count" property that you could update. The sample code you found would likely be used by your controller.