WPF 4 Plumbing and Internals

1. PDC09-CL10 WPF 4 Plumbing and Internals Blake Stone Architect Microsoft Corporation

2. WPF is Deep • WPF involves lots of interacting concepts • Layout • Animation • Styles • Templates • Binding • Events • Often many ways to accomplish a goal • Not necessarily direct parallels to Win32, WinForms, or other frameworks

3. Teaching You to Fish … • Cookbook-style programming has its place … not in this session! • You can’t reason without knowing why something works • Focus on how WPF is intendedto be used • Design principles • Implementation strategies • When all else fails:workarounds

4. Why Aren’t My Properties Set the Way I Expect? What Went Wrong? Demystifying initialization and binding

5. Evaluating XAML: What Happens When? Window Constructor • Initialized event • Fires during XAML processing • Fires on leaf nodes before their parents • Does not guarantee all properties are set • Called during the constructor that calls InitializeComponent() • Loaded events • Don’t count on the ordering InitializeComponent() Child Constructors Child Initialized Events Window Initialized Event Deferred Binding, Template Expansion, Layout, etc. Loaded Events

6. When Are My Properties Set? • It’s a trick question: property values are often sought, rather than set! • SetValue() sets local value • GetValue() returns effective value • InvalidateProperty()forces effective value update • SetCurrentValue() overrides effective value, only until the next change • Styles and animations don’t call SetValue at all! Rough search order* for effective values: 4.0 * Final value may be modified by coercion, and animated value may depend on deeper effective value

7. Binding Magic • DataContext is inherited • Data template instances given explicit context • Some properties bound two-way by default • Typically user input eg: TextBox.Text • Defined by dependency property metadata • CollectionView • Implicitly created when binding to a collection • Tracks “current” item • ItemsControl’sIsSynchronizedWithCurrentItem enables synchronized tracking* • Binding expressions now work with .NET dynamic type 4.0 * Default of null means no synchronization for default collection views, set to true or false for more control

8. Inheritance: a Tale of Two Trees* • Templates expanded lazily during layout • Inherited properties trace inheritance context • First preference is logical parent • When not present uses visual parent • Freezable subtypes have a special inheritance context • Shared freezables inherit based on where they are declared, non-shared based on where they are used • InputBinding is now Freezable <GridDataContext="Page DataContext"> <Button> <Button.Template> <ControlTemplateTargetType= “{x.TypeButton}"> <StackPanelDataContext= "Template DataContext"><ContentPresenter /> </StackPanel> </ControlTemplate></Button.Template><TextBlock Text="{Binding}" /> </Button> </Grid> Grid DC 4.0 Button StackPanel DC ContentPresenter TextBlock * The so-called “inheritance tree” doesn’t really exist, as we’ll see …

9. My Application isn’t Responsive What Went Wrong? Animations not smooth? Input being ignored?

10. Dispatcher Serializes Everything • Dispatcher runs on UI thread • All DispatcherObjectsassociated with dispatcher, single-threaded* • Processes a prioritized work queue • Long-running operations interfere with everything • Animations, input, layout, etc. • Dispatcher reentrant on Monitor.Enter() to avoid deadlocks • Used by C#’s lock() statement • Disabled via using(Dispatcher.DisableProcessing()) System.Object DispatcherObject DependencyObject Freezable Visual * Except Freezable subtypes, when frozen

11. Break Long Tasks into Bite-Sized Pieces • Use Dispatcher.BeginInvoke() • Processes work in priority order • Priority can be changed after scheduling • DispatcherTimer schedules work as Inactive, uses Win32 timer to update

12. Getting Thread-Savvy with BackgroundWorker • Long-running and blocking operations belong in worker threads • Avoid DispatcherObjectin non-UI threads • INotifyPropertyChanged across threads works • INotifyCollectionChanged does not Worker Thread Pool 100% User Code UI Thread(s) UI construction, Event listeners, Layout, Binding, etc. WPF Render Thread WPF Internal Only

13. BackgroundWorker’sThree Delegates • Once configured, BackgroundWorker coordinates work across two threads RunWorkerAsync() Worker Thread Pool UI Thread ProgressChanged 2 BackgroundWorker DoWork 1 ReportProgress() 2 RunWorkerCompleted 3

14. Why is Everything Still Sluggish? What Went Wrong? I Don’t Have Many Controls – It Must Be WPF’s Fault!

15. With Great Power Comes Great Responsibility • Visuals and framework elements do a lot • Attached properties, layout, bindings, input management, styles, and hit detection all come with a cost • Hundreds of bytes per visual • Closer to 1k for a trivial binding • Scales well to hundreds, even tens of thousands • … but Control adds templates which can generate lots of visuals • Avoid premature optimization • Use Snoop with memory and performance profiling tools to investigate observable issues • Consider OnRender() and other render data techniques • Consider cached composition with CacheMode property 4.0

16. Virtualizing Visual Trees • Why create visuals that won’t be displayed? • Virtualization is sleight-of-hand typical of long,scrolling lists • ListBox virtualizes by default, so does DataGrid • Custom ItemsPanelTemplate for an ItemsControl can use VirtualizingStackPanel • Layout can defeat virtualization when measuring unconstrained sizes • VirtualizingStackPanel.VirtualizationModesupports Recycling and GC modes 4.0

17. Only Some of My Users Have Performance Problems! • VirtualPC and “hardware rendering” can be slower than software rendering • Software rendering can be forced with HwndTarget.RenderMode = RenderMode.Software • Remote desktop • Changed regions are transmitted as bitmaps • Scrolling and animations are most obvious • Deep magic: protected VisualScrollableAreaClip property on Visual 4.0

18. So Little Time, So Many Tips! Great resources for WPF developers

19. WPF Resources

20. WPF Sessions @ PDC09 • PDC09-CL09How Microsoft Visual Studio 2010 Was Built with Windows Presentation Foundation 4 TUE 11/17/2009, 11:00AM - 12:00PM, Room 502A • PDC09-CL11Advanced Windows Presentation Foundation Application Performance Tuning and Analysis TUE 11/17/2009, 4:30PM - 5:30PM, Room Petree Hall D) • CHALK TALK Deep Dive into WPF4 Multi-Touch APIs WED 11/18/2009 11:00PM - 12:00PM, The Big Room • PDC09-CL31 Mastering WPF Graphics and Beyond WED 11/18/2009, 12:30-1:15PM, Room Hall E - 151 • PDC09-CL10Windows Presentation Foundation 4 Plumbing and Internals THUR 11/19/2009, 10:00AM - 11:00AM, Room Hall E – 151 • PDC09-CL27Multi-Touch on Microsoft Surface and Windows 7 for .NET Developers THUR 11/19/2009 , 11:30AM - 12:30PM, Room Petree Hall C • PDC09-CL24XAML Futures in Microsoft .NET Framework, Microsoft Silverlight and Tools, THUR 11/19/2009 , 1:45PM - 2:45PM, Room Hall F - 153 • MORE WPF 4 @ WPF Community sitehttp://connect.microsoft.com/wpf

21. Ask the Experts! Questions & Answers John Gossman, Mike Hillberg Architects Windows Presentation Foundation

22. YOUR FEEDBACK IS IMPORTANT TO US! Please fill out session evaluation forms online at MicrosoftPDC.com

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