Developing Windows Phone 7 Application

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 ad 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 Plateform 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

}



);


}

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.

Related Articles:

Win Phone 7: Data Binding & Storing Persistent Data Writing code

Develop Apps for Win Phone 7

Managing State in the Application Lifecycle