1. Background Service in UWP and on iOS and Android with Xamarin
NET433
Alec Tucker

2. Agenda Background Tasks vs Threading
4/20/2018 1:11 AM
Agenda
Background Tasks vs Threading
What’s Supported on Each Platform?
UWP
iOS (Xamarin)
Android (Xamarin)
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3. Background Tasks vs Threading
4/20/2018 1:11 AM
Background Tasks vs Threading
Threading to avoid blocking the UI
Critical for any “heavy” processing, comms, etc
Users expect a consistently responsive UI
Async..await provided by .Net and fully supported by Xamarin across all platforms
Running to completion when the app is closed
Exact mechanics and level of support vary by platform.
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4. What’s Supported on Each Platform
4/20/2018 1:11 AM
What’s Supported on Each Platform
Common Concepts
First, some definitions
“Tasks” in this talk refer to defined processes, rather than System.Threading.Tasks
Foreground App
The app currently on display and taking the user’s attention
By design, this gets the lion’s share of resources
Suspended App
Apps are suspended when another app demands the user’s attention (e.g. an incoming phone call)
Typically remain in memory, but get little love
Time to perform some housekeeping – usually saving state
Background App
An app that’s running in the background
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5. UWP Background Tasks Microsoft Ignite 2016 4/20/2018 1:11 AM
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6. 4/20/2018 1:11 AM
Windows Phone 8 gave us:
private void Application_Launching(object sender, LaunchingEventArgs e) {
// Called when the application is launching. Executed once }
private void Application_Activated(object sender, ActivatedEventArgs e)
// Called when the application is activated. Not called on first launch.
private void Application_Deactivated(object sender, DeactivatedEventArgs e)
// Called when the application is send to the background
private void Application_Closing(object sender, ClosingEventArgs e)
// Called when the application is closing. (Not called when deactivating)
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7. Windows 10 uses: this.Suspending += (s, e) => {
4/20/2018 1:11 AM
Windows 10 uses:
this.Suspending += (s, e) => {
// Execute code, e.g. to save state };
this.Resuming += (s, e) =>
// Execute code, e.g. to load state
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8. Extended Execution vs Background Task
4/20/2018 1:11 AM
Extended Execution vs Background Task
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9. Extended Execution Request permission Two types:
4/20/2018 1:11 AM
Extended Execution
Request permission
Two types:
One allows a little extra time to do something during app suspension (if permission granted)
The other lets the OS know this is a special kind of app which needs to run indefinitely
Neither type has any UI
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10. private async void OnSuspending(object sender, SuspendingEventArgs e)
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private async void OnSuspending(object sender, SuspendingEventArgs e) {
var deferral = e.SuspendingOperation.GetDeferral();
using (ExtendedExecutionSession session = new ExtendedExecutionSession()
Reason = ExtendedExecutionReason.SavingData,
Description = "Saving data" })
session.Revoked += (s, e) =>
// Tidy up };
switch(await session.RequestExtensionAsync())
case ExtendedExecutionResult.Allowed:
// Permission for extended execution has been granted. Save all data.
await SendAllData();
break;
case ExtendedExecutionResult.Denied:
// Permission for extended execution has been denied. Save summary
// data only as we have limited time.
await SendSummaryData(); }
deferral.Complete();
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11. ExtendedExecutionSession session = null;
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ExtendedExecutionSession session = null;
public async Task RunBackgroundTask() {
if (session == null)
session = new ExtendedExecutionSession()
Reason = ExtendedExecutionReason.SavingData,
Description = "Saving data" };
session.Revoked += (s, e) =>
// Tidy up
switch (await session.RequestExtensionAsync())
case ExtendedExecutionResult.Allowed:
// Permission for extended execution has been granted. Save all data.
await SendAllData();
break;
case ExtendedExecutionResult.Denied:
// Permission for extended execution has been denied. Save summary
// data only as we have limited time.
await SendSummaryData(); }
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12. Extended Execution vs Background Task
4/20/2018 1:11 AM
Extended Execution vs Background Task
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13. Background Tasks Background tasks can be initiated by system events
4/20/2018 1:11 AM
Invalid
SmsReceived
UserPresent
UserAway
NetworkStateChange
ControlChannelReset
InternetAvailable
SessionConnected
ServicingComplete
LockScreenApplicationAdded
LockScreenApplicationRemoved
TimeZoneChange
OnlineIdConnectedStateChange
BackgroundWorkCostChange
PowerStateChange
Background Tasks
Background tasks can be initiated by system events
Code needs to be registered with system events, or triggers
Available triggers are defined in the SystemTriggerType enum
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14. 4/20/2018 1:11 AM
public class BackgroundTask : IBackgroundTask {
private BackgroundTaskCancellationReason cancelReason =
BackgroundTaskCancellationReason.Abort;
private bool isCancelRequested = false;
private BackgroundTaskDeferral deferral = null;
public async void Run(IBackgroundTaskInstance taskInstance)
try
// Get the deferral object from the task instance
deferral = taskInstance.GetDeferral();
// Wire up a task cancellation handler
taskInstance.Canceled +=
(IBackgroundTaskInstance sender,
BackgroundTaskCancellationReason reason) =>
isCancelRequested = true;
cancelReason = reason; };
  // Check BackgroundWorkCost
// If High, then do as little work as possible and return,
// otherwise proceed as planned
switch (BackgroundWorkCost.CurrentBackgroundWorkCost) {
case BackgroundWorkCostValue.High:
// Perform only critical operations
await PerformOnlyHighPriorityOperations();
break;
case BackgroundWorkCostValue.Medium:
// Perform critical and medium priority operations
await PerformHighAndMediumPriorityOperations();
case BackgroundWorkCostValue.Low:
// Proceed with ALL desired processing
await PerformAllOperations(); }
catch (Exception ex)
// Handle the exception
finally
if (deferral != null)
deferral.Complete();
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15. InternetNotAvailable SessionConnected SessionDisconnected
4/20/2018 1:11 AM
KeyValuePair<Guid, IBackgroundTaskRegistration>? task =
(from t in BackgroundTaskRegistration.AllTasks
where t.Value.Name == taskName
select t).FirstOrDefault<KeyValuePair<Guid, IBackgroundTaskRegistration>>();
if (!task.HasValue) {
// Task is not already registered
BackgroundTaskBuilder builder = new BackgroundTaskBuilder()
Name = taskName,
TaskEntryPoint = ”Ignite2017.BackgroundTask" };
builder.SetTrigger(new SystemTrigger(SystemTriggerType.InternetAvailable, false));
builder.AddCondition(new SystemCondition(SystemConditionType.FreeNetworkAvailable));
builder.AddCondition(new SystemCondition(SystemConditionType.UserPresent));
BackgroundTaskRegistration backgroundTask = builder.Register(); }
Invalid
UserPresent
UserNotPresent
InternetAvailable
InternetNotAvailable
SessionConnected
SessionDisconnected
FreeNetworkAvailable
BackgroundWorkCostNotHigh
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16. backgroundTask.Completed +=
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backgroundTask.Completed +=
(BackgroundTaskRegistration sender, BackgroundTaskCompletedEventArgs e) => {
string taskId = sender.TaskId.ToString();
// Do what you need to with the results };
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17. iOS with Xamarin Background Tasks Microsoft Ignite 2016
© 2016 Microsoft Corporation. All rights reserved. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

18. iOS Supports Five App States
4/20/2018 1:11 AM
iOS Supports Five App States
Not running
This is as it sounds – the app is not running. It’s not been launched, or it’s been completely terminated.
Inactive
An inactive app is currently running, but is not receiving events. Apps transition through this state quickly.
Active
The app can be considered the current foreground app as per the earlier definitions. It currently has the user’s attention, and has as much access to the hardware resources of the device as is possible.
Background
The app is currently running as a registered background app, which means it’s running within the constraints described shortly. Multiple apps can be in this state.
Suspended
A suspend app resides in memory, but is not currently running.
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19. 4/20/2018 1:11 AM
iOS Lifecycle
iOS will call the following methods in your AppDelegate.cs. Override these if you want to perform specific tasks as the state changes / is about to change.
iOS Delegate
Xamarin.iOS
Description
willFinishLaunchingWithOptions
WillFinishLaunching
First method to be called. First opportunity for you to execute code at launch time
didFinishLaunchingWithOptions
FinshedLaunching
Typically where initialisation stuff goes (e.g. Xamarin.Forms). You have 17 seconds.
applicationDidBecomeInactive
OnActivated
App is about to transaction to Active and become the Foreground App
applicationWillResignActive
OnResignActivation
App is transitioning out of the Active state
applicationDidEnterBackground
DidEnterBackground
App has entered the Background state
applicationWillEnterForeground
WillEnterForeground
App is transitioning from Background into the foreground, but it’s not yet Active
applicationWillTerminate
WillTerminate
That’s all folks. If your app was already suspended it can be terminated without warning / calling this
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20. iOS Provides Three Options
4/20/2018 1:11 AM
iOS Provides Three Options
Finite Length Tasks
Have a fixed amount of time in which to complete, but do not impose restrictions on the code you can run. If it finishes in time, great. If not, it will be shut down anyway.
Long Running Tasks
Can continue without time limitations, but support only a finite set of operations, specifically:
Playing or recording audible content, location tracking VoIP, regular comms with accessories, incl Bluetooth LE, background fetch operations and remote notifications
Downloading Content
Designed for data transfer. Not time restricted. Can continue while your app is suspended or terminated. Will wake your app up and notify it on completion.
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21. iOS – Finite Length Tasks
4/20/2018 1:11 AM
iOS – Finite Length Tasks
Time constrained, NOT resource constrained
Start with:
var taskId = UIApplication.BeginBackgroundTask( OnExpiry );
Query time remaining with:
UIApplication.SharedApplication.BackgroundTimeRemaining
Critical step – end the task:
UIApplication.SharedApplication.EndBackgroundTask( taskId );
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22. iOS – Finite Length Tasks
4/20/2018 1:11 AM
iOS – Finite Length Tasks
Call EndBackgroundTask when:
The task completes successfully
The task is cancelled
The task expires
The app comes back into the foreground
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23. 4/20/2018 1:11 AM public async Task LaunchBackgroundTask() {
nint taskId = -1;
CancellationTokenSource token = new CancellationTokenSource();
// 1. Begin the background task
taskId = UIApplication.SharedApplication.BeginBackgroundTask(() =>
// Handle task expiry here
});
// 2. Perform background processing
await Task.Run(() =>
try
// Perform processing on background thread
if (token.IsCancellationRequested)
// Handle the cancellation request and clean up resources
// ...
// Alternatively (or additionally), throw and catch a
// specific type of exception
token.Token.ThrowIfCancellationRequested(); }
catch (OperationCanceledException ocEx)
// Handle task cancellation here
, token.Token );
// 3. End the background task
UIApplication.SharedApplication.EndBackgroundTask(taskId);
public override void WillEnterForeground(UIApplication uiApplication) {
if (taskId != -1)
UIApplication.SharedApplication.EndBackgroundTask(taskId); }
base.WillEnterForeground(uiApplication);
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24. iOS – Long Running Tasks
4/20/2018 1:11 AM
iOS – Long Running Tasks
Resource / operation constrained, NOT time constrained
Info.plist entries:
<key>UIBackgroundModes</key>
<array>
<string>audio</string>
<string>location</string>
<string>voip</string>
<string>newsstand-content</string>
<string>external-accessory</string>
<string>bluetooth-central</string>
<string>bluetooth-peripheral</string>
<string>fetch</string>
<string>remote-notification</string>
</array>
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25. iOS – Long Running Tasks
4/20/2018 1:11 AM
iOS – Long Running Tasks
Audio
Media framework prevents app suspension while media content is being played or recorded. When this stops, iOS proceeds with suspension.
VoIP
Suspension not prevented. iOS monitors sockets for these apps and brings them out of suspension when inbound comms are detected.
Fetch
iOS can check for new content. It will determine when this happens, and it might never happen.
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26. iOS – Long Running Tasks - Fetch
4/20/2018 1:11 AM
iOS – Long Running Tasks - Fetch
public override async void PerformFetch(
UIApplication application,
Action<UIBackgroundFetchResult> completionHandler) {
// Declare fetch result, and set default value...
UIBackgroundFetchResult fetchResult = UIBackgroundFetchResult.NoData;
try
// Fetch your data. If successful then set...
fetchResult = UIBackgroundFetchResult.NewData; }
catch
// Handle the error, and set...
fetchResult = UIBackgroundFetchResult.Failed;
finally
// Be sure to call the completion handler when we've finished
completionHandler(fetchResult);
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27. iOS – Long Running Tasks - Fetch
4/20/2018 1:11 AM
iOS – Long Running Tasks - Fetch
You can exert some control over the frequency of fetch attempts:
UIApplication.SharedApplication.SetMinimumBackgroundFetchInterval(1800);
Two constants you can make use of:
UIKit.UIApplication.BackgroundFetchIntervalMinimum
UIKit.UIApplication.BackgroundFetchIntervalNever
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28. Android with Xamarin Background Tasks Microsoft Ignite 2016
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29. Android Supports Four App States
4/20/2018 1:11 AM
Android Supports Four App States
Running
When an activity is opened by a user
Paused
When the activity view is completely or partially obscured.
Backgrounded
When the home button is pressed, or when the app switcher button is pressed.
The app remains in memory in this state.
Stopped
When the back button is pressed, or when memory is low.
The app is removed from memory in this state.
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30. Android Lifecycle We’re able to override the following: OnCreate()
4/20/2018 1:11 AM
Android Lifecycle
We’re able to override the following:
OnCreate()
OnStart()
OnPause()
OnResume()
OnStop()
OnRestart()
OnDestroy()
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31. Android Lifecycle Action Calls Launch app OnCreate() OnStart()
4/20/2018 1:11 AM
Android Lifecycle
Action
Calls
Launch app
OnCreate()
OnStart()
OnResume()
Pause app
OnPause()
Resume paused app
Background the app
OnStop()
Restart backgrounded app
OnRestart()
Stop backgrounded app
OnDestroy()
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32. 4/20/2018 1:11 AM
Android Services
An application component that can perform long running tasks without a UI
[Android.App.Service]
public class MyAndroidService : Android.App.Service {
public override Android.OS.IBinder OnBind(Android.Content.Intent intent)
throw new System.NotImplementedException(); }
As resources dwindle, Android will go on the hunt for things to kill, starting with activities and moving on to services.
If the OS does kill your service, you can configure it to restart once sufficient resources become available
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33. Android Services Services should not be started like this:
4/20/2018 1:11 AM
Android Services
Services should not be started like this:
MyAndroidService service = new MyAndroidService();
Rather they should be started via an Intent.
[Android.App.Service]
public class MyAndroidService : Android.App.Service {
public override Android.App.StartCommandResult OnStartCommand(
Android.Content.Intent intent,
Android.App.StartCommandFlags flags,
int startId)
return base.OnStartCommand(intent, flags, startId); }
public override Android.OS.IBinder OnBind(Android.Content.Intent intent)
throw new System.NotImplementedException();
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34. Android Services Value Action NotSticky
4/20/2018 1:11 AM
Android Services
StartCommandResult will contain one of the following values:
Value
Action
NotSticky
Service will not be restarted if killed. Typical for processes that can be retried without adverse impact, e.g. periodic checking a web service for data updates
RedeliverIntent
If killed, this service will be scheduled to be restarted, and the last delivered intent will be redelivered
Sticky
Restart if killed. No intent will be passed in
StickyCompatibility
A compatibility version of Sticky for older versions (older than API15). Does not guarantee that OnStartCommand will be called
It’s important that OnStartCommand returns one of these values as quickly as possible. This means that you’ll need to start a separate thread within your service.
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35. Android Services So to start and stop your services, use: For example:
context.StartService()
contect.StopService()
For example:
StartService(new Android.Content.Intent(this, typeof(MyAndroidService)));
StopService(new Android.Content.Intent(this, typeof(myAndroidService)));
Services can also stop themselves using:
this.StopSelf()
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36. Android Services - Binding
4/20/2018 1:11 AM
Android Services - Binding
What about background services that interact with the UI of your app?
Android lets us bind to a service
It will shut down the service when all clients have unbound
Hybrid – common use. Example:
An app that tracks location and shows location info in the UI
Start the service when the app is launched
Communicate with it
Leave it running when the app is terminated
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37. 4/20/2018 1:11 AM public class TimeTrackingServiceBinder : Binder {
public TimeTrackingService Service { get; private set; }
public TimeTrackingServiceBinder(TimeTrackingService pService)
this.Service = pService; }
public class TimeTrackingService : Service {
// Declare a timer which will fire every minute
private Timer TimeTracker = new Timer(60000);
public EventHandler<ElapsedEventArgs> TimerElapsed;
public override Android.OS.IBinder OnBind(Android.Content.Intent intent)
return new TimeTrackingServiceBinder(this); }
public override StartCommandResult OnStartCommand(
Android.Content.Intent intent, StartCommandFlags flags, int startId)
TimeTracker.Elapsed += TimeTracker_Elapsed;
TimeTracker.Start();
return StartCommandResult.Sticky;
public override void OnDestroy()
TimeTracker.Elapsed -= TimeTracker_Elapsed;
base.OnDestroy();
private void TimeTracker_Elapsed(object sender, ElapsedEventArgs e)
this.TimerElapsed(this, e);
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38. 4/20/2018 1:11 AM
public class TimeTrackingServiceConnection : IServiceConnection {
public void OnServiceConnected(ComponentName name, Android.OS.IBinder service)
throw new System.NotImplementedException(); }
public void OnServiceDisconnected(ComponentName name)
public System.IntPtr Handle
get { throw new System.NotImplementedException(); }
public void Dispose()
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39. 4/20/2018 1:11 AM
public class TimeTrackingServiceConnection : Java.Lang.Object, IServiceConnection {
private IBinder binder;
public event EventHandler<ServiceEventArgs> ConnectionChanged = delegate { };
public TimeTrackingService Service
get
TimeTrackingServiceBinder serviceBinder
= binder as TimeTrackingServiceBinder;
return serviceBinder != null ? serviceBinder.Service : null; }
public void OnServiceConnected(ComponentName name, Android.OS.IBinder service)
= service as TimeTrackingServiceBinder;
if (serviceBinder != null)
this.binder = serviceBinder;
ConnectionChanged(this, new ServiceEventArgs(true));
public void OnServiceDisconnected(ComponentName name)
ConnectionChanged(this, new ServiceEventArgs(false));
this.binder = null;
public class ServiceEventArgs : EventArgs {
public bool IsConnected { get; private set; }
public ServiceEventArgs(bool pIsConnected)
IsConnected = pIsConnected; }
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40. 4/20/2018 1:11 AM public class ServiceManager {
private static Lazy<ServiceManager> serviceManager
= new Lazy<ServiceManager>(() => new ServiceManager());
public static ServiceManager Current
get { return serviceManager.Value; } }
private TimeTrackingServiceConnection serviceConnection;
public TimeTrackingService TimeTrackingService
get
return serviceConnection.Service;
public event EventHandler<ServiceEventArgs> ConnectionChanged = delegate { };
private ServiceManager()
Task.Run(() =>
Intent intent = new Intent(
Application.Context, typeof (TimeTrackingService));
// Start the service...
Application.Context.StartService(intent);
// ...and bind to it
serviceConnection = new TimeTrackingServiceConnection();
serviceConnection.ConnectionChanged += (s, e) =>
ConnectionChanged(this, e);
Application.Context.BindService(
intent, serviceConnection, Bind.AutoCreate);
});
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41. ServiceManager.Current.ConnectionChanged += (s, e) => {
4/20/2018 1:11 AM
ServiceManager.Current.ConnectionChanged += (s, e) => {
if (e.IsConnected)
ServiceManager.Current.TimeTrackingService.TimerElapsed += OnTimerElapsed; }
else
ServiceManager.Current.TimeTrackingService.TimerElapsed -= OnTimerElapsed; };
private void OnTimerElapsed(object sender, System.Timers.ElapsedEventArgs e)
// Do something here with e
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42. Android Services Lifecycle Event Action OnCreate
4/20/2018 1:11 AM
Android Services
Finally, we should also be doing the following:
Lifecycle Event
Action
OnCreate
Wire up the ConnectionChanged event on the previous slide
OnPause
Unwire the TimerElapsed event to prevent it from firing
OnRestart
Wire the TimerElapsed event up again
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43. Summary UWP iOS (Xamarin) Android (Xamarin)
Extended Processing vs Background Tasks
iOS (Xamarin)
Finite Length Tasks vs Long Running Tasks
Android (Xamarin)
Android Services and Binding
© 2014 Microsoft Corporation. All rights reserved. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

44. Continue your Ignite learning path
4/20/2018 1:11 AM
Continue your Ignite learning path
Visit Channel 9 to access a wide range of Microsoft training and event recordings
Head to the TechNet Eval Centre to download trials of the latest Microsoft products
Visit Microsoft Virtual Academy for free online training visit
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45. Thank you Chat with me in the Speaker Lounge Find me @alecdtucker
4/20/2018 1:11 AM
Thank you Chat with me in the Speaker Lounge Find
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