lessons learned from developing a windows 8 metro application in c# frode nilsen nilsen labs ticki

Lessons learned from developing a Windows 8 Metro application in C#

Frode NilsenNilsen Labs

Ticki

Agenda

Async-await done right

Applying the MVVM pattern in Windows 8

Unscientific comparison of MS XAML technologies

The async-await pattern

What it is

What it not is

Pitfalls

Applying it properly

Background

Feb 2012: Introduced in .Net 4.5 Spring 2011: Async CTP

June 2008: Task Parallel Library (TPL, .NET 4.0)

The basics

Two new c# keywords: async and await

Makes asyncronous programming easy

Makes asyncronous code clean

The old way

The new way

The new way

1

2

Defintion: Asynchrony

«Not at the same time»

When method returns to the caller

When the caller gets the return value

Threads

Going deeper

Async part 1, part 2 NDC 2012 presentation Lucian Wischik (Microsoft Senior Program Manager)

The Task Asynchronous Pattern (TAP) paperby Stephen Toub Feb 2012 (Microsoft Async Guru) Progress reporting

Cancellation

Retrying

Interleaving

Throttling

The power of asynchronous programming - example

Option 1 – Serially

Rq 1 Rq 2 Rq 3

Time

Rq 4

Option 2 – In Parallel

Rq 1

Rq 2

Rq 3

Time

Rq 4

Request slot 2

Request slot 1

Option 3 – Throttled parallelism

Rq 1

Rq 2 Rq 3

Rq 4

Time

Google «AsyncSemaphore»

DEMO – the powers of Tasks

Async pitfalls 1 : Blocking threads

• Task.Wait()• Task.Result

Async pitfalls 2 : Deadlocks

Async pitfalls 3 : Exceptions

Async pitfalls 4 : async void

Rule of thumbs for async await

Never return async void from a method, unless it’s a UI event handler

Always await async methods.If you want to run several tasks in parallel, use await Task.WhenAll() or await Task.WhenAny()

Never use Task.Wait() or Task.Result to «synchronify» async methods, except in unit tests.

Never do async calls from constructors

MVVM in Windows 8

Recap of the gist

Applying it to Windows 8

Pitfalls

Tools and tips

MVVM Model

View

ViewModel

Send notificationsData binding

and commands

Send notifications

Updates

From MSDN

MVVM Model

View

ViewModel

Send notificationsData binding

and commands

Send notifications

UpdatesDATABINDING

Things that are impossible to do directly from the ViewModel

Give a visual element focus

Select text in a text box

Scroll an item into view

Show / hide Charms, App-or Navigation-bar

MVVM

“MVVM is targeted at modern UI development platforms which support Event-driven programming”

Quotes from the Wikipedia article

MVVM

“MVVM is targeted at modern UI development platforms which support Event-driven programming”

Quotes from the Wikipedia article

DEMO - events

Controls and DataContext

A B C

A

ViewModels

Controls

B C D E

A ListView

Controls and DataContext

A B C

A

ViewModels

Controls

B C D E

A ListView

Controls and DataContext

A B C

A

ViewModels

Controls

B C D E

A ListView

D E

F

Controls and DataContext

AB C

A

ViewModels

Controls

B C D E

A ListView

D E

F

Solution: Pub/sub-pattern

Messenger

Publisher 1

Publisher 2

Publisher 2

Subscriber 1

Subscriber 2

Subscriber 2

Solution: Pub/sub-pattern

Messenger

Publisher 1

Publisher 2

Publisher 2

Subscriber 1

Subscriber 2

Subscriber 2

User controlsViewModels

Solution: Pub/sub-pattern

Messenger

Publisher 1

Publisher 2

Publisher 2

Subscriber 1

Subscriber 2

Subscriber 2MVVM Light Toolkit

link

DEMO – pub/sub

MVVM

“MVVM was designed to make use of data binding functions in WPF to better facilitate the separation of view layer development from the rest of the pattern by removing virtually all GUI code (“code-behind”) from the view layer”

Quotes from the Wikipedia article

Things that are impossible to do directly from the ViewModel

Give a visual element focus

Select text in a text box

Scroll an item into view

Show / hide Charms, App-or Navigation-bar

Things I thought were impossible, but were not

Trigger animations Achieved through the use of databound visual states and

attached properties

Alter the layout of a grid You can databind Grid.ColumnDefinition.Width

You can databind visibility of sections within the grid

Windows 8 XAML vs «other XAML»

Example 1: Bundled controls

Example 1: Bundled controls

WinForm SL Win8

Button X X X

DatePicker X X

DataGrid X X

TreeView X X

ComboBox X X

TabControl X X

Grid X X

StackPanel X X

MediaElement X X

Making your own controls

Templates

Visual tree vs Logical tree

Custom dependency properties

Custom events

Example 2: Databinding

Binding update on property changed

WinForms

WPF

Silverlight

• No UpdateSourceTrigger

WinRT

• No UpdateSourceTrigger

• No BindingOperations.GetBinding()

WinRT 2 (a slightly better alternative)

link

Microsoft XAML technologies

WPF

Silverlight

Windows Phone 7

Windows 8 (WinRT)

Time

Qu

ality

Thank you

Mail: nilsenlabs@gmail.com

Twitter: @nilzor

Blog: www.nilzorblog.com

Q & A