Develop Reference

Why did I have to use Task<T> to acheive Synchronous calls?

Im working on a website that integrates with Dynamics 365 with the Dynamics SDK. We have seen errors in the logs such as “Cannot access a disposed object”. Upon further investigation we found out that the SDK methods are not thread safe so needed to refactor the code to take this into account.
We had a method such as follows that would create or update a Contact entity depending on whether it already exists:
public Guid? SetProfile(IProfile profile)
{
using (var xrm = new XrmServiceContext(_organizationService))
{
//check whether account already exists
var crmProfile = GetContact(xrm, profile.UserId);
if (crmProfile == null)
{
//create new account if required
{
crmProfile = new Contact
{
EMailAddress1 = profile.Username,
//lots of properties hidden to make for easier code example
};
}
xrm.AddObject(crmProfile);
}
else
{
//update existing account
crmProfile.new_Title = profile.Title.HasValue ? new OptionSetValue(profile.Title.Value) : null;
//lots of properties hidden to make for easier code example
xrm.UpdateObject(crmProfile);
}
var response = xrm.SaveChanges();
return crmProfile.Id;
}
}
When this method was executed concurrently by 2 or more users the error "Cannot access a disposed object" would be thrown, referring to the XrmServiceContext object.
I therefore knew that I needed to make this method thread-safe, but also it needs to be Synchronous as our UI depends on having the return value of the method. I played around with different threading methods:
Task.Factory.StartNew(() => delegate
new Thread()
However, with both of these methods I wasn't able to get the method to execute synchronously, so I ended up with:
public Guid? SetProfile(IProfile profile)
{
var task = new Task<Guid?>(() =>
{
using (var xrm = new XrmServiceContext(_organizationService))
{
//check whether account already exists
var crmProfile = GetContact(xrm, profile.UserId);
if (crmProfile == null)
{
//create new account if required
{
crmProfile = new Contact
{
EMailAddress1 = profile.Username,
//lots of properties hidden to make for easier code example
};
}
xrm.AddObject(crmProfile);
}
else
{
//update existing account
crmProfile.new_Title = profile.Title.HasValue ? new OptionSetValue(profile.Title.Value) : null;
//lots of properties hidden to make for easier code example
xrm.UpdateObject(crmProfile);
}
var response = xrm.SaveChanges();
return crmProfile.Id;
}
});
task.RunSynchronously();
return task.Result;
}
Everything I seemed to read online suggested I should use the StartNew method, however this is geared towards Asynchronous calls with I could not allow, and it also seemed that it doesnt guarantee a new thread - from what I've read I understand it is clever enough to know when it needs to create a new thread - however in my instance I have to be certain a new thread is used for the call to Dynamics.
Questions:
Anything wrong with the approach I've taken for a Web application?
If I can't use Asynchronous calls, is there any advantage whatsoever to using the StartNew method?
Many thanks for your time in advance
Kind regards
dotdev

Android Activity destroyed when calling ZXing barcode scanner. How to recover?

First of all, I'm using, Xamarin with MvvmCross.
In my ViewModel, I'm using the ZXing MobileBarcodeScanner class to scan a barcode when the user clicks a button:
var scanner = new MobileBarcodeScanner();
var result = await scanner.Scan();
if (result != null)
{
CodigoProduto = result.Text;
InternalPesquisarProduto();
}
After the scan, I run the InternalPesquisarProduto void, that search for data on a remote server, based of course, on the barcode that was read. This method, also display some loading message while the data is fetched:
Ui.DisplayLoading("Searching...", "Searching data");
// Code that fetches the data
Ui.DismissLoading();
The Ui is a property on my ViewModel defined like this:
protected IUiInteractor Ui { get; set; }
I receive it by dependency injection. Here is the relevant code from the implementation being used in this scenario:
public class AndroidUiInteractor : IUiInteractor
{
private IMvxAndroidCurrentTopActivity _mvxCurrentTopActivity;
public AndroidUiInteractor(IMvxAndroidCurrentTopActivity mvxCurrentTopActivity)
{
_mvxCurrentTopActivity = mvxCurrentTopActivity;
}
public void DisplayLoading(string title, string message)
{
_mvxCurrentTopActivity.Activity.RunOnUiThread(() =>
{
_progressDlg = new ProgressDialog(_mvxCurrentTopActivity.Activity);
// Configuring the title and the message
_progressDlg.Show();
});
}
}
The problem is that when the scanner.Scan is called, my caller activity is destroyed, so when I call the Ui.DisplayLoading, the _mvxCurrentTopActivity.Activity is null.
What is most weird about this case, is that I have two Samsungs with Android 5.0 API 21 that I use in my tests, and this problem only happens in one of them, on the other, the activity is not destroyed when calling the scanner.Scan.
Note: I'm sorry for anything wrong in the code, but because of company policies, I can only access the internet by Terminal Service, and the Ctrl + V is disabled on it.

It turns out the problem was in the device. After reseting it's configurations it worked properly.
This might not be a definitive solution for everyone that faces that problem, but in my scenario it could be done.

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.

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.

Windows Phone Live SDK API - get new session object after restarting the App

so I have succeeded in connecting my Windows Phone 8 Application to the Live API, I also succeeded in reading data from my hotmail account.
I have access to the needed client ID and the live access token.
But when I quit and restart my application, I lose all references to the session and the client objects and I have to start the process anew.
I don't want to annoy the user with the web mask in which he has to agree again that he provides me with the needed permissions every time he is starting the application. But I also haven't found a way to get a reference to a session object without this step.
The login mask is only shown the first time after installing the application, after that, only the screen mentioned above is shown.
But it is still quite annoying for the user to accept this every time.
I already tried serializing the session object, which is not possible, because the class does not have a standard constructor.
Maybe it is possible to create a new session by using the live access token, but I haven't found a way to do so.
Any ideas? What am I doing wrong, I know that there is a way to login again without prompting the user.
I'm thankful for every idea.
Some code I use:
/// <summary>
/// This method is responsible for authenticating an user asyncronesly to Windows Live.
/// </summary>
public void InitAuth()
{
this.authClient.LoginCompleted +=
new EventHandler<LoginCompletedEventArgs>(this.AuthClientLoginCompleted);
this.authClient.LoginAsync(someScopes);
}
/// <summary>
/// This method is called when the Login process has been completed (successfully or with error).
/// </summary>
private void AuthClientLoginCompleted(object sender, LoginCompletedEventArgs e)
{
if (e.Status == LiveConnectSessionStatus.Connected)
{
LiveConnector.ConnectSession = e.Session; // where do I save this session for reuse?
this.connectClient = new LiveConnectClient(LiveConnector.ConnectSession);
// can I use this access token to create a new session later?
LiveConnector.LiveAccessToken = LiveConnector.ConnectSession.AccessToken;
Debug.WriteLine("Logged in.");
}
else if (e.Error != null)
{
Debug.WriteLine("Error signing in: " + e.Error.ToString());
}
}
I have tried to use the LiveAuthClient.InitializeAsync - method to login in background after restarting the application, but the session object stays empty:
// this is called after application is restarted
private void ReLogin()
{
LiveAuthClient client = new LiveAuthClient(LiveConnector.ClientID);
client.InitializeCompleted += OnInitializeCompleted;
client.InitializeAsync(someScopes);
}
private void OnInitializeCompleted(object sender, LoginCompletedEventArgs e)
{
Debug.WriteLine("***************** Inititalisation completed **********");
Debug.WriteLine(e.Status); // is undefined
Debug.WriteLine(e.Session); // is empty
}
Does anyone have an idea how I could get access to a new session after restarting the application?

After two full days searching for the mistake I was making, I finally found out what I was doing wrong: I have to use the wl.offline_access scope to make this work!
Let me quote another user here:
"If your app uses wl.offline_access scope than the live:SignInButton control saves it for you and loads it automatically. Just use the SessionChanged event to capture the session object. This way the user will need to sign in only once."
(see WP7 how to store LiveConnectSession during TombStoning?)
Now everything is fun again. Can't believe that this was the problem. Tested & working. Nice!

Been struggling to get this working on a Windows Live + Azure Mobile Service app myself so thought I would post a complete working code sample here now that I've got it working.
The key parts are the wl.offline_access scope and the call to InitializeAsync.
Note: this sample also connects with Windows Azure Mobile Services. Just remove the stuff related to MobileService if you're not using that.
private static LiveConnectSession _session;
private static readonly string[] scopes = new[] {"wl.signin", "wl.offline_access", "wl.basic"};
private async System.Threading.Tasks.Task Authenticate()
{
try
{
var liveIdClient = new LiveAuthClient("YOUR_CLIENT_ID");
var initResult = await liveIdClient.InitializeAsync(scopes);
_session = initResult.Session;
if (null != _session)
{
await MobileService.LoginWithMicrosoftAccountAsync(_session.AuthenticationToken);
}
if (null == _session)
{
LiveLoginResult result = await liveIdClient.LoginAsync(scopes);
if (result.Status == LiveConnectSessionStatus.Connected)
{
_session = result.Session;
await MobileService.LoginWithMicrosoftAccountAsync(result.Session.AuthenticationToken);
}
else
{
_session = null;
MessageBox.Show("Unable to authenticate with Windows Live.", "Login failed :(", MessageBoxButton.OK);
}
}
}
finally
{
}
}