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W8 Unwrapping the not- so-obvious Kevin Dockx | 05/03/2013

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2012 Microsoft Corporation. All rights reserved.

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Agenda Navigation, Suspension Manager & complex types Manipulating the navigation stack Handling exceptions in awaitable methods that arent awaited Implementing a Variable Sized Grid Incrementally loading data Debugging background tasks

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Agenda Can you get local host access? Async & Await: theres more to it Performance tips & tricks The most important tip of this session Q&A

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Suspension manager? Implementation included in Store Apps Allows you to save & restore state of a View Makes it easy to support PLM for simple apps, but for larger apps, youll probably want your own way to handle PLM

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Suspension manager? Saves and restores the navigation state of the Frame Crashes when you pass in a complex object private static void SaveFrameNavigationState(Frame frame) { var frameState = SessionStateForFrame(frame); frameState["Navigation"] = frame.GetNavigationState(); }

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Support complex objects? Simple approach: pass in simple types If you must: (de)serialize yourself JsonHelper class JsonHelper.ToJson when navigating JsonHelper.FromJson in LoadState

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Rgis Laurent Director of Operations, Global Knowledge Competencies include: Gold Learning Silver System Management Demo

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Manipulating the Navigation Stack Why would you want to do this? Typically: showing a disclaimer, an initial wizard, Check for value in Application Settings to see if page has to be shown Use Frame.SetNavigationState(1,0,0) to remove all pages from the stack

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Rgis Laurent Director of Operations, Global Knowledge Competencies include: Gold Learning Silver System Management Demo

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Exceptions in Async methods Awaitable methods arent always awaited In such a case, when Exception happens => NOT caught by App_UnhandledException What if you still want to know about it? Handle the TaskScheduler.UnobservedTaskException event

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Rgis Laurent Director of Operations, Global Knowledge Competencies include: Gold Learning Silver System Management Demo

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Implementing a VariableSizedWrapGrid Create your own GridView class, inherit from GridView Override PrepareContainerForItemOverride Set RowSpan & ColumnSpan VariableSizedWrapGrid.SetRowSpan VariableSizedWrapGrid.SetColumnSpan

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Implementing a VariableSizedWrapGrid In XAML, use the newly created GridView Set the ItemPanelTemplate to a VariableSizedWrapGrid Optionally define the orientation Optionally define the maximum number of rows/columns Typically, define ItemHeight & ItemWidth

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Rgis Laurent Director of Operations, Global Knowledge Competencies include: Gold Learning Silver System Management Demo

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Incrementally loading data An old trick Create a style for your ListViewBase (ListView, GridView) Handle the ScrollViewers ViewChanged event, check the offset value a better implementation Bind to a collection that supports incremental loading Create a collection, inherit from ObservableCollection Implement ISupportIncrementalLoading

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Rgis Laurent Director of Operations, Global Knowledge Competencies include: Gold Learning Silver System Management Demo

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Debugging a Background Task Look for the Debug Location Toolbar Its hidden by default!

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Rgis Laurent Director of Operations, Global Knowledge Competencies include: Gold Learning Silver System Management Demo

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Localhost access? No. And theres a good reason for that. Did I say no? I meant yes. Due to a loopback rule, access to localhost is restricted When youre in Visual Studio, your app is exempted from this loopback rule => Allow Local Network loopback You can manually exempt your app, using CheckNetIsolation.exe: CheckNetIsolation.exe LoopbackExempt a p=AppID

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Async & Await Support Cancellation Accept a Cancellation Token in your method signature Check for cancellation in that method Handle OperationCancelledException

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Async & Await UI thread marshalling is what you get for free Do you always want this? How can you avoid this? await YourAsyncMethod().ConfigureAwait(false);

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Async & Await Waiting for Any or All Tasks to complete var firstCompleted = await Task.WhenAny( SomeAwaitableMethod1(), SomeAwaitableMethod2(), SomeAwaitableMethod3()); => returns the first completed task result var allCompleted = await Task.WhenAll( SomeAwaitableMethod1(), SomeAwaitableMethod2(), SomeAwaitableMethod3()); => returns a list of all results of all tasks

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Performance tip #1 Obvious, but maybe not so much: check performance in Release Builds Writing to the output window slows down your app tremendously Use the Performance Profiler

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Peformance tip #2 Use the Async & Await tips Cancel running operations when not needed Execute Tasks in Parallel when possible Do not marshal to the UI thread when its not necessary

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Performance tip #3 Reduce memory consumption Obvious? Yes, but for an additional reason The less memory your app uses, the more likely it is to stay in memory instead of being terminated, ensuring a faster restart after being suspended

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Performance tip #4 Learn about XAML parsing Do not load resources that arent necessary Resource Dictionaries are fully parsed, even though your page might only use one resource of it Your start page shouldnt use application-wide dictionaries If you use a resource throughout your app, put it in Application If you dont, only reference that dictionary on the pages it is used, or even in the page-specific resource dictionary

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Performance tip #4 Optimize element count Dont write this: But write this:

Slide 39 "> "> " title="Performance tip #4 Reuse brushes Dont write this: Write this:

Performance tip #4 Reuse brushes Dont write this: Write this: