In this example I will demonstrate a very simple call to the FlickR REST APIs from a Silverlight client. At the end we will end up with an app that looks like this:

image

Part 1. Define some Silverlight UI

Part 2. Show the local open file dialog support

Part 3. Call the FlickR Service to find a picture

Part 4. Use IsolatedStorage to preserve some local settings across runs

Part 5. Skinning the UI

You are welcome to also get the completed sample, and demo files

Part 1. Define some Silverlight UI

You can go back and look at the post on my End to End Silverlight Application post for the getting started.  In Blend add a TextBox, and Button to the window and layout as shown. 

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Be sure to give them some meaningful name in the properties window so we can refer to them pragmatically later.   Mine are called searchTermTextBox, and button. 

Drag an example image on to the window so we can have something to work with.  (You can use cow.jpg from the SilverlightFlickRDemoFiles zip)

image

Make sure you name this one as well... I used searchResultsImage

Part 2. Local Open File Dialog

Just to test out our layout, add support for popping open the open file dialog and work with the image client side.  This is something that you can't readily do in Ajax\HTML today.

In page.xaml Add a Click event handler

<Button x:Name="button" Width="100" Height="50" 
        Content="Go"
        Click="button_Click"

In page.xaml.cs implement the button click to call open file dialog.

    private void button_Click(object sender, RoutedEventArgs e)
    {
        OpenFileDialog ofd = new OpenFileDialog();
        ofd.Filter = "JPEG Files (*.jpg;*.jpeg)|*.jpg;*.jpeg | All Files (*.*)|*.*";
        ofd.FilterIndex = 1;

        if (ofd.ShowDialog() == DialogResult.OK) {
            Stream stream = ofd.SelectedFile.OpenRead();
            BitmapImage bi = new BitmapImage();
            bi.SetSource(stream);
            searchResultsImage.Source = bi;
            stream.Close();
        }
    }

This code will open the system open file dialog allowing the user to select a file on disk.  Then the developer is given only save access to the file (that is just the bits, not hte path to the file).  Notice how we are able to work with the image client slide. 

image

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At this point you could upload the file to a server or store it locally in Isolated Storage.   But this is a little off from where we were going with searching flickr for an image..

Part 3. Call the FlickR Service to find a picture

Now we get into the meat of it.   We need to pass our search term into FlickRs REST API and set the image to be the results.  As the user clicks on the image, we can show the next one in the results set. 

First we need to call FlickRs REST API.  To do this you need a key, which you can get for free from FlickR...

Next we need to actually call the REST API from the Silverlight client.  To do that, let's define a helper method

void LoadPhotos(string topic)
{
    string apiKey = "<<get your own >>";
    string secret = "<<get your own >>";
    string url = String.Format("http://api.flickr.com/services/rest/?method=flickr.photos.search&api_key={1}&text={0}",
       topic, apiKey, secret);
    WebClient flickRService = new WebClient();
    flickRService.DownloadStringCompleted += new DownloadStringCompletedEventHandler(flickRService_DownloadStringCompleted);
    flickRService.DownloadStringAsync(new Uri(url));
searchTermTextBox.Text = "Calling FlickR...";
}

 

Next we need to parse the results.  You can see the format of the results by looking at http://flickr.com/services/api/explore/ .  Basically, the results look like this:

<?xml version="1.0" encoding="utf-8" ?>
<rsp stat="ok">
  <photos page="1" pages="32769" perpage="100" total="3276843">
    <photo id="2436622217" owner="22956152@N04" secret="6c8293bb5c" server="2070" farm="3" title="IMG_3492_resize" ispublic="1" isfriend="0" isfamily="0" />
    <photo id="2437437876" owner="41848473@N00" secret="97a7e1a066" server="2303" farm="3" title="Eric & Dog" ispublic="1" isfriend="0" isfamily="0" />
  </photos>
</rsp>
  

So, we need to do a little Xml parsing.  Luckily this is very easy to do in Silverlight with LinqToXml support.   Just add a reference to the System.Xml.linq.dll  assembly.

image

Now let's implement flickRService_DownloadStringCompleted.  The first thing we need to do is a little error checking... This will help a lot making sure everything is right calling FlickR.

XDocument xmlPhotos = XDocument.Parse(e.Result);
if (e.Error != null ||
    xmlPhotos.Element("rsp").Attribute("stat").Value == "fail"){
    string results = e.Result;
    searchTermTextBox.Text= "Error! (" + results + ")";
    return;
}
else {
    searchTermTextBox.Text = "It worked!";
}

Now we just need to wire up the call to LoadPhotos.

private void button_Click(object sender, RoutedEventArgs e)
{
    LoadPhotos(searchTermTextBox.Text);
}

Run it.  If you see this, go back and check your API key.

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When you see this, you are golden and ready for the next step!

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Now, we need to parse the Xml results and pull out the URLs to the image.  We are going to use the magic of Linq to handle all the ugly Xml parsing.  All we need to do is to define a .NET class we want the XML elements mapped into.

public class FlickRPhoto
{
    public string Id { get; set; }
    public string Owner { get; set; }
    public string Secret { get; set; }
    public string Server { get; set; }
    public string Farm { get; set; }
    public string Title { get; set; }
}

And, let's just add another property that class which follows the FlickR URL conventions for form up a Url to the image

public string ImageUrl
{
    get
    {
        return string.Format("http://farm{0}.static.flickr.com/{1}/{2}_{3}.jpg",
            Farm,Server,Id,Secret);
    }
}

Now, we need the Linq code that maps the Xml elements into this class.

Photos = from photo in xmlPhotos.Element("rsp").Element("photos").Descendants().ToList()
         select new FlickRPhoto
         {
             Id = (string)photo.Attribute("id"),
             Owner = (string)photo.Attribute("owner"),
             Secret = (string)photo.Attribute("secret"),
             Server = (string)photo.Attribute("server"),
             Farm = (string)photo.Attribute("farm"),
             Title = (string)photo.Attribute("title"),
         };

Let's define Photos as a field on this class, so we can access it later.

IEnumerable<FlickRPhoto> Photos;

Now we just need to display the image. To do that, we just grab the first record from the result set and display it! 

FlickRPhoto p = Photos.First();
this.searchResultsImage.SetValue(Image.SourceProperty, p.ImageUrl);
searchTermTextBox.Text = p.Title;

Now that is cool, but I want to see the other photos.. A quick a dirty way to do this is to change the photo when the photo is clicked.  To do this sign up for the event handler

 

<Image MouseLeftButtonDown="searchResultsImage_MouseLeftButtonDown" 
             x:Name="searchResultsImage" 

And implement it.  I  do a little error checking up front, and use a new class field called ImageNumber to keep up with here I am.

private void searchResultsImage_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
    if (Photos == null) return;
    if (ImageNumber >= Photos.Count()) ImageNumber = 0;

    FlickRPhoto p = Photos.Skip(ImageNumber).First();
    this.searchResultsImage.SetValue(Image.SourceProperty, p.ImageUrl);

    ImageNumber++;

}

Now as you click on the picture, it cycles you through the result set

image

Part 4: Use IsolatedStorage to preserve some local settings across runs

Now, let's see about preserving some of this state across runs. 

First, let's save off the results of the textbox when the "Go" button is pressed. 

private void button_Click(object sender, RoutedEventArgs e)
{
    LoadPhotos(searchTermTextBox.Text);
    ApplicationSettings.Default["searchTerm"] = txtBox.Text;
    ApplicationSettings.Default.Save();

}

and the same idea when the image changes

private void searchResultsImage_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
    if (Photos == null) return;
    if (ImageNumber >= Photos.Count()) ImageNumber = 0;

    FlickRPhoto p = Photos.Skip(ImageNumber).First();
    this.searchResultsImage.SetValue(Image.SourceProperty, p.ImageUrl);
    searchTermTextBox.Text = p.Title;

    ApplicationSettings.Default["imageNumber"] = ImageNumber;
    ApplicationSettings.Default.Save();

    ImageNumber++;

}

Then when the application starts up we can pull the latest set and initialize with it. 

public Page() {
    InitializeComponent();
    if (ApplicationSettings.Default.Contains("searchTerm")){
        this.txtBox.Text = (string)ApplicationSettings.Default["searchTerm"];
        button_Click(null, null);
    }
    if (ApplicationSettings.Default.Contains("imageNumber")){
        ImageNumber = (int)ApplicationSettings.Default["imageNumber"];
    }
}

When you run it the first time, it has not saved state so it uses the default.  But run it again and notice it picks up where you left off! 

Part 5: Skin it

Now, let's give it a nice skin.  Again, I will use Corrina's Rough Skin

Just cut and paste the <ApplicationResources> section from Corrina's example into your App.Xaml

Then add the styles

<Button Style="{StaticResource buttonStyle}"
<TextBox Style="{StaticResource textBoxStyle}" 

Done!

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You are welcome to also get the completed sample, and demo files

Update (6/19/08):  I updated this sample for Silveright Beta2...