WPF 4 Plumbing and Internals

Blake StoneArchitectMicrosoft Corporation

PDC09-CL10

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

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 intended

to be used> Design principles> Implementation strategies

> When all else fails:workarounds

Why Aren’t My Properties Set the Way I Expect?

Demystifying initialization and binding

What Went Wrong?

Window Constructor

Evaluating XAML: What Happens When?> 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

Loaded Events

Deferred Binding, Template Expansion,

Layout, etc.

Window Initialized Event

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

Animated value

Local value

“Setter” in style trigger

Setter in style

Inherited value

* Final value may be modified by coercion, and animated value may depend on deeper effective value

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’s IsSynchronizedWithCurrentItem enables synchronized tracking*

> Binding expressions now work with .NET dynamic type4.0

* Default of null means no synchronization for default collection views, set to true or false for more control

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

* The so-called “inheritance tree” doesn’t really exist, as we’ll see …

Grid

Button

TextBlock

StackPanel

ContentPresenter

<Grid DataContext="Page DataContext"> <Button> <Button.Template> <ControlTemplate TargetType= “{x.Type Button}"> <StackPanel DataContext= "Template DataContext"> <ContentPresenter /> </StackPanel> </ControlTemplate> </Button.Template> <TextBlock Text="{Binding}" /> </Button></Grid>

DC

DC

4.0

My Application isn’t Responsive

Animations not smooth? Input being ignored?

What Went Wrong?

Dispatcher Serializes Everything

> Dispatcher runs on UI thread> All DispatcherObjects associated

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

Visual

* Except Freezable subtypes, when frozen

Freezable

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

Send Normal

DataBind Render

Loaded Input

Background

ContextIdle

ApplicationIdle

SystemIdle

Inactive

Worker Thread Pool

100% User Code

Getting Thread-Savvy with BackgroundWorker

> Long-running and blocking operations belong in worker threads

> Avoid DispatcherObject in non-UI threads> INotifyPropertyChanged across threads

works> INotifyCollectionChanged does not

WPF Render Thread

WPF Internal Only

UI Thread(s)

UI construction,Event listeners,Layout, Binding,

etc.

UI Thread Worker Thread Pool

DoWork

BackgroundWorker’s Three Delegates> Once configured, BackgroundWorker

coordinates work across two threads

RunWorkerCompleted

ProgressChanged

BackgroundWorker

ReportProgress()

1

2

2

3

RunWorkerAsync()

Why is Everything Still Sluggish?

I Don’t Have Many Controls – It Must Be WPF’s Fault!

What Went Wrong?

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

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.VirtualizationMode

supports Recycling and GC modes

4.0

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

So Little Time, So Many Tips!

Great resources for WPF developers

WPF ResourcesInformation Sources

Portal for WPF and WinForms

http://windowsclient.net/wpf

WPF Forum http://social.msdn.microsoft.com/forums/en-US/wpf/threads

WPF SDK Portal http://msdn.microsoft.com/en-us/library/ms754130.aspx

Lester Lobo on new WPF 4 features

http://blogs.msdn.com/llobo/archive/tags/New+WPF+4+features/default.aspx

WPF 4 text features http://blogs.msdn.com/text/archive/tags/WPF+4.0/default.aspx

Mike Hillberg’s Blog http://blogs.msdn.com/mikehillbergTools

Snoop http://www.blois.us/Snoop

Mole for Visual Studio http://www.codeproject.com/KB/WPF/MoleForWPF.aspx

WPF Performance Suite http://windowsclient.net/wpf/perf/wpf-perf-tool.aspx

WPF Toolkit http://wpf.codeplex.com/Release/ProjectReleases.aspx?ReleaseId=29117

WPF Sessions @ PDC09> PDC09-CL09 How Microsoft Visual Studio 2010 Was Built with Windows

Presentation Foundation 4 TUE 11/17/2009, 11:00AM - 12:00PM, Room 502A

> PDC09-CL11 Advanced 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-CL10 Windows Presentation Foundation 4 Plumbing and Internals THUR 11/19/2009, 10:00AM - 11:00AM, Room Hall E – 151

> PDC09-CL27 Multi-Touch on Microsoft Surface and Windows 7 for .NET Developers THUR 11/19/2009 , 11:30AM - 12:30PM, Room Petree Hall C

> PDC09-CL24 XAML 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 site http://connect.microsoft.com/wpf

Ask the Experts!

John Gossman, Mike HillbergArchitectsWindows Presentation Foundation

Questions & Answers

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