Developing Windows Phone 7 application

BANGALORE, INDIA: At MIX 10, Microsoft gave a first look at developer platform for new Windows Phone 7. They have designed this new phone operating system ground up starting from approach to hardware to the user experience for the phone and from app platform to tools that let you build new applications.

This article will focus on the developer platform, which is based on Silverlight and XNA, aspect of this new phone. Both Silverlight and XNA platforms expose set of APIs that let developers use C# to build rich applications or games. On top of base Silverlight/ XNA platform, Windows Phone 7 application platform adds functionality that is phone specific. Windows Phone Developer Platform consists of four big components (NETCF: set of base class libraries, Silverlight: Presentations/Media framework, XNA: Game framework, Windows Phone specific APIs).

Developers will be able to use familiar Silverlight tools such as Microsoft VS 2010 and Microsoft Expression Blend. Friction free acquisition was the primary goals for these tools. It means there is one simple setup that gets you everything that you need and you can get started with the Windows Phone at zero cost. For this new express edition of Visual Studio, Microsoft Visual Studio Express for Windows Phone is created. It provides free tooling to get started on Windows Phone 7development.This set of tools has a completely revised device emulator which lets you run your applications in Windows Phone OS without having Windows Phone device. This emulator is not only much faster than the previous version but provides high fidelity environment since it is running Windows Phone 7 OS and supports graphics acceleration.

Navigation Model

Navigation based UX model is one of the core concepts for Windows Phone 7 and one of the three keys a developer will find on every phone that runs Windows Phone 7 is the back key. Just like web, Navigation refers to the ability to link pages with hyperlinks where the user can navigate back and forth.

Namespace: System.Windows.Navigation

Creating a linked page can be as simple as writing a line of XAML or code. Or NavigationService.Navigate(new Uri("/Page1.xaml",

UriKind.Relative));

Developer could also pass query parameters via URIs.

NavigationService.Navigate(new

Uri("/Page1.xaml?username=vivekd", UriKind.Relative));

One the target page (Page1.xaml) in this case, user can get access to this query parameter: string username; if (NavigationContext.QueryString.TryGetValue("username", out username))

textBlock1.Text = username;

Media



MediaElement class can play Media (Play(), Stop()) by either

taking URI or Stream to media source as input.

mediaElement1.Play();

mediaElement1.Stop();

Media on Windows Phone is hardware accelerated which not only makes it fast but also power efficient. On phone, SL applications can also take advantage of sounds APIs from XNA for supporting polyphonic sounds.

Windows Phone Developer Platform Components

WebBrowser

WebBrowser control lets you host HTML inside your application without having to launch a separate browser process for scenarios such as advertisement or RSS feeds or emails.

Namespace: Microsoft.Phone.Control

x:Class="WindowsPhoneApplication1.MainPage"

...

xmlns:browser="clrnamespace:

Microsoft.Phone.Controls;assembly=Microsoft.Phone

.Controls.WebBrowser">

This XAML will host the MSN.com home page within a Windows Phone Application. WebBrowser control could also load html from string using WebBrowser control's Navigate-ToString(string) method.

string html = //get a stream of html from website or local html

and convert it to string

webBrowser1.NavigateToString(html);

WebBrowser control has APIs that let the application developer interact with JavaScript inside the html page that is hosted. This functionality is disabled by default but can be enabled by setting IsScriptEnabled property to true. When this is enabled, C# code in WP7 application can call into Javascript using Invoke- Script method. Javascript uses window.external.Notifty method to push data to managed application. Developer needs to subscribe to ScriptNotify event to receive this data.

function CallFromSilverlight(input)

{

textbox.value = input;

return true;

}

function CallFromScript()

{

window.external.Notify(textbox.value);

}

If we had html that contained above script then following code will call CallFromSilverlight function in Javascript and pass in arguments from managed C# application to that function.Javascript on the page

webBrowser1.InvokeScript("CallFromSilverlight", arg);

In the ScriptNotify event handler, NotifyEventArgs will contain the actual data passed in by Javascript.

private void webBrowser1_ScriptNotify(object sender, NotifyEventArgse)

{

textBox1.Text = e.Value;

}

Accelerometer

Accelerometer sensor lets the developer figure out the orientation of the device in the space, by sending samples of g-forces along X, Y and Z axis with a timestamp. This is particularly useful in games such as car racing where device orientation is used as an input for actions in games.

Namespace: Microsoft.Devices.Sensors

acc = AccelerometerSensor.Default;

acc.ReadingChanged += new EventHandler(

acc_ReadingChanged);

acc.Start();

In the ReadingChanged event handler you would use AccelerometerReadingAsyncEventArgs to get to actual values of gforces along different axis. void acc_ReadingChanged(object sender, Accelerometer- ReadingAsyncEventArgs e)

{ Dispatcher.BeginInvoke(() =>

{

//physics engine code

});

}

Launchers and Choosers

Launchers and Choosers are the way to leverage in built OS experiences for certain tasks such as taking a photo, or selecting a contact.

- Launchers let the developer launch to an OS application. E.g. Developer wants to send email programmatically.

- Choosers are more like functions; they do some task and then come back to application with data. E.g. Twitter application wants to choose a photo from album and post the photo.

Namespace: Microsoft.Phone.Tasks

PhotoChooserTask photopicker = new PhotoChooserTask(); photopicker.Show(); Developer needs to call Show() method on a Task. Chooser returns the data to page (PhoneApplicationPage class) via OnChooserReturn virtual method.public override void OnChooserReturn(object sender, EventArgs e)

{

TaskEventArgs args = e as TaskEventArgs;

if (args != null && args.TaskResult == TaskResult.OK &&

args.Result.ChosenPhoto != null)

{

Stream photoStream = args.Result.ChosenPhoto;

//use the stream to display photo

}

}

Stream for Data returned by chooser is available via TaskEventArgs.Results APIs.

Location

Location: Actual location could be decided via a variety of different methods such as WiFi, GPS or cell phone tower triangulation. Location Service can map geo location to civic address. Mapping is one of the primary applications on today's smartphones. A developer using Location APIs is not aware of actual method used for location is abstracted out. Developer needs to provide desired accuracy (Low or high) while using location APIs and right method is used.

Namespace: System.Device.Location

GeoCoordinateWatcher watcher = new GeoCoordinate- Watcher(GeoPositionAccuracy.Low);

 watcher.PositionChanged += new EventHandler>( watcher_PositionChanged); CivicAddressResolver resolver = new CivicAddressResolver(); resolver.ResolveAddressCompleted += newEventHandler( resolver_ResolveAddressCompleted);

watcher.Start(); Developer will hook into PositionChanged event of GeoCoordinateWatcher class and get access to location data via GeoPositionChangedEventArgs.

void watcher_PositionChanged(object sender, GeoPosition- ChangedEventArgs e)

{

Dispatcher.BeginInvoke(() =>

{

resolver.ResolveAddressAsync(e.Position.Location);

}

);

}

Developer will use CivicAddressResolver. ResolveAddressAsynch where raw geo coordinates are passed to cloud service which will resolve the position in longitude/ latitude and map it to civic address. ResolveAddressCompleted event handler gets called with resolved civic address void resolver_ResolveAddressCompleted(object sender, ResolveAddressCompletedEventArgs

e)

{

Dispatcher.BeginInvoke(() =>

{ //use e.Address.AddressLine1 etc APIs to get the actual address

}

);

}

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Push Notification

Scenarios such as news or stock updates require user to get notification on the phone even when application is not running. Push notification service solves this problem by providing an URI where app service could post data whenever event happens. After this point, Microsoft Push service will take care of delivering this data as a notification to the phone. Sequence of action depicting steps that happen between applications opening channel for push notification to data getting delivered to device.

Namespace: Microsoft.Phone.Notification

HttpNotificationChannel channel = new HttpNotificationChannel("

channelforvivek");

channel.Open();

channel.ChannelUriUpdated += new EventHandler(

channel_ChannelUriUpdated);

Developer will call Open () method on an instance of HttpNotificatioChannel. Once the push services returns an URI to developer via ChannelUriUpdated event, developer will need to pass on the URI to the service. After this point, service will post the new data to the URI and it will get delivered to phone.Sequence of action depicting steps that happen between applications opening channel for push notification to data getting delivered to device.