The game itself is from another sample, the Windows Phone 7 Platformer Starter Kit from David Rousset's blog.

The changes are to add code to run UDP Multicast sockets and to enable multiplayer. 

The source code for the full project is attached in the zip file below.

PlatformerGame.cs:  This contains the game code and is where the sockets are initialized, and where the sends and receives are handled. 

UdpAnySourceMulticastChannel.cs: This contains the UDP multicast sockets code for joining the group, sending and receiving data.

OtherPlayer.cs:  This is a modification of Player.cs to add other players to the game.

Sockets Initialization in PlatformerGame.cs:

private void InitializeSockets() { this.Channel = new UdpAnySourceMulticastChannel(IPAddress.Parse("224.109.108.107"), 3007); this.Channel.PacketReceived += new EventHandler<UdpPacketReceivedEventArgs>(Channel_PacketReceived); this.Channel.Open(); } 

This joins the UdpAnySourceMulticastClient group and sets it up to receive data: 

 public void Open() { if (!IsJoined) { this.Client.BeginJoinGroup( result => { try { this.Client.EndJoinGroup(result); IsJoined = true; this.OnAfterOpen(); this.Receive(); } catch { } }, null); } } private void Receive() { if (IsJoined) { Array.Clear(this.ReceiveBuffer, 0, this.ReceiveBuffer.Length); this.Client.BeginReceiveFromGroup(this.ReceiveBuffer, 0, this.ReceiveBuffer.Length, result => { if (!IsDisposed) { IPEndPoint source; try { this.Client.EndReceiveFromGroup(result, out source); this.OnReceive(source, this.ReceiveBuffer); this.Receive(); } catch { IsJoined = false; this.Open(); } } }, null); } }

Each time a player moves, it sends its new position and velocity to the multicast group.

 private void SendPosition(string position) { if (level.Player.Position.X != oldPosition.X || level.Player.Position.Y != oldPosition.Y) { oldPosition = level.Player.Position; this.Channel.Send(position); } }

This sends the packet to the multicast group.

 public void Send(string format, params object[] args) { if (IsJoined) { byte[] data = Encoding.UTF8.GetBytes(string.Format(format, args)); this.Client.BeginSendToGroup(data, 0, data.Length, result => { this.Client.EndSendToGroup(result); }, null); } }

When a packet gets received, the receive handler updates the other player so that it looks like the other player is moving. Each phone in the multicast group receives this and updates accordingly.

 void Channel_PacketReceived(object sender, UdpPacketReceivedEventArgs e) { string data = e.Message; Console.WriteLine(data); string[] pos = data.Split(','); //Discard packets that do not match if (pos.Length != 5) { return; } try { if (pos[0] != identifier.ToString()) //if not originated from this phone { if (pos[1].Contains("ReachedExit")) { level.TimeRemaining = TimeSpan.Zero; } else { Vector2 position = new Vector2(float.Parse(pos[1]), float.Parse(pos[2])); Vector2 velocity = new Vector2(float.Parse(pos[3]), float.Parse(pos[4])); level.UpdateOtherPlayer(int.Parse(pos[0]), position, velocity); } } } catch (Exception ex) { System.Diagnostics.Debug.WriteLine("Caught unexpected exception: " + ex.Message); } }

To play, use the accelerometer to move left or right. Tap on the screen to jump. Multiplayer requires WiFi network.

To get the Windows Phone Mango Developer Tools Beta: https://www.microsoft.com/downloads/en/details.aspx?FamilyID=77586864-ab15-40e1-bc38-713a95a56a05&displaylang=en

Hope this helps show a simple way to communicate from phone to phone and demonstrate the power of sockets.  Happy developing!

Ricky

WindowsPhonePlatformer.zip

More and more training materials are becoming available.  There was a training course called the Windows Phone 7 Jump Start that was released last week.  It is for all developers interested in developing applications or games for the Windows Phone 7 platform, and includes 12 hours of classroom training and supporting exercises.

 There is also the Windows Phone 7 Developer Training Kit which provides a step-by-step explanation of all the tools to use and some key concepts for programming Windows Phones.

The application bar icons used can be downloaded for free at: https://www.microsoft.com/downloads/details.aspx?FamilyID=369b20f7-9d30-4cff-8a1b-f80901b2da93 

First, create a new Windows Phone Application project.  Add the files for the ApplicationBar icons to the project for play and pause, and change their Build Action to "Content".

Then update the xaml MainPage.xaml to add a MediaElement and the ApplicationBar:

    <Grid x:Name="LayoutRoot" Background="Transparent">

        <Grid.RowDefinitions>

            <RowDefinition Height="*"/>

        </Grid.RowDefinitions>

        <MediaElement Source="https://www.rickytan.net/media/Butterfly.wmv" AutoPlay="True" x:Name="mediaElement1" />

    </Grid>

    <phone:PhoneApplicationPage.ApplicationBar>

        <shell:ApplicationBar IsVisible="True" IsMenuEnabled="True">

            <shell:ApplicationBarIconButton x:Name="appbar_button1" IconUri="appbar.transport.play.rest.png" Text="Play" Click="appbar_button1_Click"/>

            <shell:ApplicationBarIconButton x:Name="appbar_button2" IconUri="appbar.transport.pause.rest.png" Text="Pause" Click="appbar_button2_Click"/>

            <shell:ApplicationBar.MenuItems>

                <shell:ApplicationBarMenuItem x:Name="menuItem1" Text="Media Player Launcher" Click="menuItem1_Click" />

            </shell:ApplicationBar.MenuItems>

        </shell:ApplicationBar>

    </phone:PhoneApplicationPage.ApplicationBar>

Finaly, update the code in MainPage.xaml.cs to hook up the Play, Pause and MediaPlayerLauncher events:

        MediaPlayerLauncher mediaPlayerLauncher;

        public MainPage()

        {

            InitializeComponent();

            mediaPlayerLauncher = new MediaPlayerLauncher();

        }

        private void appbar_button1_Click(object sender, EventArgs e)

        {

            mediaElement1.Play();

        }

        private void appbar_button2_Click(object sender, EventArgs e)

        {

            mediaElement1.Pause();

        }

        private void menuItem1_Click(object sender, EventArgs e)

        {

            mediaPlayerLauncher.Media = new Uri("https://www.rickytan.net/media/Butterfly.wmv", UriKind.Absolute);

            mediaPlayerLauncher.Show();

        }

 To enable the app to run in landscape mode, change the SupportedOrientations in MainPage.xaml to PortraitOrLandscape: 

SupportedOrientations="PortraitOrLandscape"

Below is the list of Launchers:

EmailComposeTask launches the Email application which displays a new email message.

MarketplaceDetailTask launches the Windows Phone Marketplace client application which then shows the details page for a product specified by the unique identifier you provide.

MarketplaceHubTask launches the Windows Phone Marketplace client application.

MarketplaceDetailTask launches the Windows Phone Marketplace client application which then displays the review page for your application.

MarketplaceSearchTask launches the Windows Phone Marketplace client application which then shows the search results based on search terms you provide.

MediaPlayerLauncher launches the Media Player application and plays the media file you specify.

PhoneCallTask launches the Phone application and displays the specified phone number and display name. The phone call is not placed until it is initiated by the user.

SearchTask launches the Search application and performs search query you provide.

SmsComposeTask launches the Messaging application which displays a new SMS message.

WebBrowserTask launches the Web browser and displays the URL you provide.

And below is the list of Choosers:

CameraCaptureTask launches the Camera application for the user to take a photo.

EmailAddressChooserTask launches the Contacts application and allows the user to select a contact's email address.

PhoneNumberChooserTask launches the Contacts application and allows the user to select a contact's phone number.

PhotoChooserTask launches the Photo Picker application for the user to choose a photo.

SaveEmailAddressTask saves the provided email address to the Contacts list.

SavePhoneNumberTask saves the provided phone number to the Contacts list.

For an example of how they work, I'll use a modification of my previous slideshow sample to add images to the slideshow from the photos stored on the phone and from the camera capture. 

First, add the namespace:

using Microsoft.Phone.Tasks; 

Then add the following code:

        PhotoChooserTask photoChooserTask;

        CameraCaptureTask cameraCaptureTask;

        //CameraCaptureTask completed event handler. Set the image source to the captured photo and add it to the list of images.

        void cameraCaptureTask_Completed(object sender, PhotoResult e)

        {

            if (e.TaskResult == TaskResult.OK)

            {

                BitmapImage bmp = new BitmapImage();

                bmp.SetSource(e.ChosenPhoto);

                Image1.Source = bmp;

                images.Add(bmp);

            }

        }

        //PhotoChooserTask completed event handler. Set the image source to the chosen photo and add it to the list of images.

        void photoChooserTask_Completed(object sender, PhotoResult e)

        {

            if (e.TaskResult == TaskResult.OK)

            {

                BitmapImage bmp = new BitmapImage();

                bmp.SetSource(e.ChosenPhoto);

                Image1.Source = bmp;

                images.Add(bmp);

            }

        }

        private void CameraCaptureButton_Click(object sender, RoutedEventArgs e)

        {

            cameraCaptureTask.Show();

        }

        private void PhotoChooserButton_Click(object sender, RoutedEventArgs e)

        {

            photoChooserTask.Show();

        }

Then add the following initialization code to the constructor public MainPage() after InitializeComponent();

            photoChooserTask = new PhotoChooserTask();

            photoChooserTask.Completed += new EventHandler<PhotoResult>(photoChooserTask_Completed);

            cameraCaptureTask = new CameraCaptureTask();

            cameraCaptureTask.Completed += new EventHandler<PhotoResult>(cameraCaptureTask_Completed);

Finally, add a button for CameraCaptureButton_Click and a button for PhotoChooserButton_Click.  Then run the app and click on those buttons to see CameraCaptureTask and PhotoChooserTask.  The image returned by either task will get added to the slideshow and be displayed as the current image.

The CTP version of the emulator doesn't come with any photos to import, but you can add some pictures using Internet Explorer.  Launch Internet Explorer, find an image you want to use, then click and hold on the image.  You'll get the option to "save picture".

Fortunately there is a workaround.  Jeff Wilcox has written about this in his blog, so if you have an Indeterminate ProgressBar, you can add this workaround: https://www.jeff.wilcox.name/2010/08/performanceprogressbar/

To update the previous slideshow sample to download images from an online site, set the URI to the http link of the image:

    string source = "https://..."; //add link to your image

    BitmapImage bitmapImage = new BitmapImage(new Uri(source, UriKind.Absolute));

    bitmapImage.DownloadProgress += new EventHandler<DownloadProgressEventArgs>(bitmapImage_DownloadProgress);

    image1.Source = bitmapImage;

To show download progress to the user, handle the DownloadProgress to update a ProgressBar with the download progress.

    void bitmapImage_DownloadProgress(object sender, DownloadProgressEventArgs e)

    {

        progressBar1.Value = e.Progress;

    }

 Xaml (this uses the PerformanceProgressBar workaround from Jeff's blog post, and the ManipulationDelta and ManipulationCompleted events handlers from my previous blog post to add gestures handling to the image):

        <StackPanel x:Name="stackPanel1" HorizontalAlignment="Center" VerticalAlignment="Center">

            <TextBlock Text="Downloading image. Please wait." HorizontalAlignment="Center" VerticalAlignment="Center" />

            <ProgressBar x:Name="progressBar1" Width="300" Height="30" Minimum="0" Maximum="100" />

            <ProgressBar x:Name="progressBar2" IsIndeterminate="True" Width="300" Height="30" Style="{StaticResource PerformanceProgressBar}" />

        </StackPanel>

        <Border BorderThickness="3" BorderBrush="Silver">

            <Image x:Name="image1" ManipulationDelta="image1_ManipulationDelta" ManipulationCompleted="image1_ManipulationCompleted">

                <Image.RenderTransform>

                    <TransformGroup>

                        <ScaleTransform x:Name="scale" />

                        <TranslateTransform x:Name="translate" />

                    </TransformGroup>

                </Image.RenderTransform>

            </Image>

        </Border>

The Silverlight Bing Map control allows you to integrate an immersive mapping solution with gestures-enabled zooming and panning in your Windows Phone applications.

The Pivot and Panorama are the navigation controls that are used extensively on Windows Phone 7.  The difference is that the Pivot is a lot like the TabControl designed for the phone, while the Panorama offers a unique way to view content by using a long horizontal canvas that extends beyond the confines of the screen.

A Map control:

A Pivot containing a WebBrowser and a TextBox:

And a Panorama containing a couple of TextBox controls: 

To use these controls, right-click on References in the Solution Explorer and add reference to Microsoft.Phone.Controls and Microsoft.Phone.Controls.Maps.  Then add the following xmlns declaration to your xaml:

xmlns:controls="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone.Controls"

xmlns:map="clr-namespace:Microsoft.Phone.Controls.Maps;assembly=Microsoft.Phone.Controls.Maps"

 Xaml for the Map control:

    <Grid x:Name="LayoutRoot" Background="Transparent">

        <map:Map ZoomBarVisibility="Visible" ZoomLevel="12" Center="47.63641255621237, -122.13312149047851" />

    </Grid>

Xaml for the Pivot containing a WebBrowser and a TextBox:

         <controls:Pivot>

            <controls:Pivot.Background>

                <ImageBrush ImageSource="Lighthouse.jpg" />

            </controls:Pivot.Background>

            <controls:PivotItem Header="WebBrowser">

                <phone:WebBrowser Name="webBrowser1" Source="https://www.bing.com" />

            </controls:PivotItem>

            <controls:PivotItem Header="TextBox">

                <TextBox />

            </controls:PivotItem>

        </controls:Pivot>

Xaml for the Panorama containing a couple of TextBox controls:

        <controls:Panorama>

            <controls:Panorama.Background>

                <ImageBrush ImageSource="Lighthouse.jpg" />

            </controls:Panorama.Background>

            <controls:PanoramaItem Header="TextBox">

                <TextBox />

            </controls:PanoramaItem>

            <controls:PanoramaItem Header="More Text" >

                <TextBox />

            </controls:PanoramaItem>

        </controls:Panorama>

Note: I've omitted the CredentialsProvider property setting on the Map control, so if you run this xaml, you'll see some text on the map to sign up for a Bing Maps developer account.  You can sign up for free at https://www.bingmapsportal.com/.

Edit:  I've separated the Map, Pivot and Panorama controls.  Also added that these new controls will be in the next release of the free developer tools as they didn't make the beta.

To briefly explain what these gestures are:

• The Pan gesture is where the user touches the screen with a finger and moves the finger on the touch screen.  In today's sample, the Pan gesture is used to change the Translate transform value to move the image on the screen, and is implemented in image1_ManipulationDelta.
• The Flick gesture is similar to the Pan gesture, but is inertial, where the user moves the finger quickly and lifts the finger.  The Flick gesture will be used to change the image source to the next or previous image, depending on the direction of the Flick.  This is implemented in image1_ManipulationCompleted.
• The Pinch gesture uses two fingers to pinch the screen, this will be used to change the Scale transform value to resize the image smaller.  This is implemented in image1_ManipulationDelta.
• The Stretch gesture, which is the opposite of the Pinch gesture, uses two fingers to stretch the screen - this will be used to resize the image larger.  Since Pinch is just the opposite of Stretch, they share the same code.

Since it is possible in this sample to move the image off the screen, or pinch it into a size that is too small to resize back, I've added a button to revert to default.  Below is what it looks like after a couple of Flicks to get to the Penguins, a Stretch to resize the image larger, and a Pan to move the image down and centered on the penguins:

Xaml:

    <Grid x:Name="LayoutRoot" Background="Transparent">

        <Grid.RowDefinitions>

            <RowDefinition Height="*"/>

            <RowDefinition Height="Auto"/>

        </Grid.RowDefinitions>

        <Canvas x:Name="ContentGrid">

            <Image x:Name="Image1" Source="Koala.jpg" ManipulationDelta="Image1_ManipulationDelta"  ManipulationCompleted="image1_ManipulationCompleted">

                <Image.RenderTransform>

                    <TransformGroup>

                        <ScaleTransform x:Name="scale" ScaleX="0.47" ScaleY="0.47" />

                        <TranslateTransform x:Name="translate" />

                    </TransformGroup>

                </Image.RenderTransform>

            </Image>

        </Canvas>

        <Button Content="Revert to Default" Grid.Row="1" Click="Button_Click" />

    </Grid>

Code:

    public partial class MainPage : PhoneApplicationPage

    {

        List<string> files = new List<string>() { "Koala.jpg", "Jellyfish.jpg", "Penguins.jpg" };

        List<BitmapImage> images = new List<BitmapImage>();

        int current = 0;

        // Constructor

        public MainPage()

        {

            InitializeComponent();

            foreach (string file in files)

            {

                BitmapImage image = new BitmapImage(new Uri(file, UriKind.Relative));

                images.Add(image);

            }

        }

        private void image1_ManipulationCompleted(object sender, ManipulationCompletedEventArgs e)

        {

            //if a pan or flick gesture, scale is 0

            if (e.TotalManipulation.Scale.X == 0 && e.TotalManipulation.Scale.Y == 0)

            {

                //if event occurs during inertia, it is a flick, so go to the previous or next image

                if (e.IsInertial)

                {

                    //use the X translation to determine whether to go to previous or next

                    double translation = e.TotalManipulation.Translation.X;

                    if (translation > 0)

                    {

                        Previous();

                    }

                    else

                    {

                        Next();

                    }

                    //revert the translate from the ManipulationDelta event so that only the image source changes

                    translate.X -= e.TotalManipulation.Translation.X;

                    translate.Y -= e.TotalManipulation.Translation.Y;

                }

            }

        }

        private void Image1_ManipulationDelta(object sender, ManipulationDeltaEventArgs e)

        {

            //handle stretch or pinch gestures by changing the scale

            if (e.DeltaManipulation.Scale.X != 0 && e.DeltaManipulation.Scale.Y != 0)

            {

                scale.ScaleX *= e.DeltaManipulation.Scale.X;

                scale.ScaleY *= e.DeltaManipulation.Scale.Y;

            }

            //handle pan gesture

            translate.X += e.DeltaManipulation.Translation.X;

            translate.Y += e.DeltaManipulation.Translation.Y;

        }

        private void Button_Click(object sender, RoutedEventArgs e)

        {

            scale.ScaleX = 0.45;

            scale.ScaleY = 0.45;

            translate.X = 0;

            translate.Y = 0;

        }

        private void Previous()

        {

            current--;

            if (current < 0)

                current = files.Count - 1;

            Image1.Source = images[current];

        }

        private void Next()

        {

            current++;

            if (current >= files.Count)

                current = 0;

            Image1.Source = images[current];

        }

    }

1. CheckBox - to toggle slideshow on/off

2. TextBox - to display the file name

3. Image - to display the image

4. ProgressBar - to display progress

For this sample slideshow application, drag and drop some images from your Sample Pictures folder to your project.  I used Koala.jpg, Jellyfish.jpg and Penguins.jpg.

This is the xaml:

    <Grid x:Name="LayoutRoot" Background="Transparent">

        <Grid.RowDefinitions>

            <RowDefinition Height="Auto"/>

            <RowDefinition Height="Auto"/>

            <RowDefinition Height="*"/>

            <RowDefinition Height="Auto"/>

        </Grid.RowDefinitions>

        <CheckBox Content="Slideshow Mode" Checked="CheckBox_Checked" Unchecked="CheckBox_Unchecked" IsChecked="True"  />

        <Grid x:Name="TitlePanel" Grid.Row="1">

            <Grid.ColumnDefinitions>

                <ColumnDefinition Width="Auto"/>

                <ColumnDefinition Width="*"/>

                <ColumnDefinition Width="Auto"/>

            </Grid.ColumnDefinitions>

            <TextBlock VerticalAlignment="Center" Text="File name: " />

            <TextBox Grid.Column="1" x:Name="textBox1" />

        </Grid>

        <Grid x:Name="ContentGrid" Grid.Row="2">

            <Image x:Name="Image1" />

        </Grid>

        <ProgressBar x:Name="ProgressBar1" Grid.Row="3" />

    </Grid>

And this is the code:

    public partial class MainPage : PhoneApplicationPage

    {

        DispatcherTimer timer = new DispatcherTimer();

        List<string> files = new List<string>() { "Koala.jpg", "Jellyfish.jpg", "Penguins.jpg" };

        List<BitmapImage> images = new List<BitmapImage>();

        int current = 0;

        // Constructor

        public MainPage()

        {

            InitializeComponent();

            ProgressBar1.Maximum = files.Count;

            foreach (string file in files)

            {

                BitmapImage image = new BitmapImage(new Uri(file, UriKind.Relative));

                images.Add(image);

            }

            timer = new DispatcherTimer();

            timer.Interval = TimeSpan.FromSeconds(2);

            timer.Tick += new EventHandler(timer_Tick);

            timer.Start();

        }

        void timer_Tick(object sender, EventArgs e)

        {

            Image1.Source = images[current];

            textBox1.Text = files[current];

            ProgressBar1.Value = current;

            current++;

            if (current >= files.Count)

                current = 0;

        }

        private void CheckBox_Checked(object sender, RoutedEventArgs e)

        {

            timer.Start();

        }

        private void CheckBox_Unchecked(object sender, RoutedEventArgs e)

        {

            timer.Stop();

        }

    }

Navigation

In desktop Silverlight, the application's RootVisual is the startup page, and setting the RootVisual changes the page.  In Silverlight for Windows Phone 7, the application's RootVisual is a PhoneApplicationFrame, which has navigation events for page navigation.  To navigate to a page:

NavigationService.Navigate(new Uri("/Page1.xaml", UriKind.RelativeOrAbsolute));

Try this out by adding a new Windows Phone Page named "Page1.xaml", and add the code above to a button click event handler.  Run the application and click on the button to navigate to Page1.  To go back to the previous page, press the hardware Back button.

Saving State

One main difference on the phone is that user responsiveness and battery life are high priorities.  So applications will not be left running all the time like on the desktop.  This makes saving application state important, so that next time the application starts, the user can continue where he/she left off.

To save application state, you can use IsolatedStorageSettings.ApplicationSettings in the System.IO.IsolatedStorage namespace.  In this example, we’ll have a simple application that contains:

1.       The Navigate button described above

2.       TextBox for entering a URL

3.       WebBrowser control

4.       Go button to navigate to the URL. The URL in the TextBox will be saved when the Go button is pressed.

This is the design surface:

This is the xaml in MainPage.xaml:

    <Grid x:Name="LayoutRoot" Background="Transparent">

        <Grid.RowDefinitions>

            <RowDefinition Height="Auto"/>

            <RowDefinition Height="Auto"/>

            <RowDefinition Height="*"/>

        </Grid.RowDefinitions>

        <Button Content="Navigate to Page1" Click="Button_Click" />

        <Grid x:Name="TitlePanel" Grid.Row="1">

            <Grid.ColumnDefinitions>

                <ColumnDefinition Width="Auto"/>

                <ColumnDefinition Width="*"/>

                <ColumnDefinition Width="Auto"/>

            </Grid.ColumnDefinitions>

            <TextBlock Grid.Column="0" x:Name="ApplicationTitle" VerticalAlignment="Center" Text="URL: " />

            <TextBox Grid.Column="1" x:Name="textBox1" />

            <Button Grid.Column="2" Content="Go" Click="Button_Click_1" />

        </Grid>

        <Grid x:Name="ContentGrid" Grid.Row="2">

            <phone:WebBrowser Name="webBrowser1" Source="https://www.bing.com" />

        </Grid>

    </Grid>

And this is the code in MainPage.xaml.cs:

    public partial class MainPage : PhoneApplicationPage

    {

        public MainPage()

        {

            InitializeComponent();

            this.Loaded += new RoutedEventHandler(WebBrowserPage_Loaded);

        }

        void WebBrowserPage_Loaded(object sender, RoutedEventArgs e)

        {

            string url = null;

            if (IsolatedStorageSettings.ApplicationSettings.Contains("textbox"))

            {

                url = IsolatedStorageSettings.ApplicationSettings["textbox"].ToString();

            }

            if (url != null)

            {

                textBox1.Text = IsolatedStorageSettings.ApplicationSettings["textbox"].ToString();

                webBrowser1.Source = new Uri(textBox1.Text, UriKind.Absolute);

            }

            else

            {

                textBox1.Text = "https://www.bing.com";

            }

        }

        private void Button_Click(object sender, RoutedEventArgs e)

        {

            NavigationService.Navigate(new Uri("/Page1.xaml", UriKind.RelativeOrAbsolute));

        }

        private void Button_Click_1(object sender, RoutedEventArgs e)

        {

            webBrowser1.Source = new Uri(textBox1.Text, UriKind.Absolute);

            IsolatedStorageSettings.ApplicationSettings["textbox"] = textBox1.Text;

            IsolatedStorageSettings.ApplicationSettings.Save();

        }

    }

So in this sample application, the URL is persisted in IsolatedStorageSettings.ApplicationSettings["textbox"], so that the application remembers the last URL that the user browsed to.