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Silverlight + PageMethods

Having attending this year's MVP Summit, I have to say I am even more interested in writing some Silverlight applications.  One of the questions I am trying to answer is just how to get Silverlight to talk to the server, especially when it comes to DotNetNuke integration.  Some quick searching yielded this excellent blog on how Silverlight and javascript can interact.  I thought it may be helpful to some people to see how to allow Silverlight to call into a PageMethod and pass and return a rich object.  I admit this may not be the best option, as I still need to do some research, but at a bare minimum this approach should allow a Silverlight developer to easily invoke a DotNetNuke Control Method

Here are the simple steps to get things working using Silverlight Beta 1 code.

1)  Create your Page Method (C# default.aspx.cs)

public static Dictionary<string, string> TestDict(Dictionary<string, string> dict)
  if (dict.Count > 0)
    dict.Add("Server", "cool!");
  return dict;

2)  Create a simple button on your page .xaml and hook it up to a Click handler. (Page.xaml)

<Button Width="100" Content="Dictionary" Click="Dictionary_Click" />

3)  Since PageMethods are asynchronous calls, when they are invoked, we need to give a callback function pointer (delegate) for it to notify us when it is complete or failed.  So we need to define a new delegate with the following signature (C# - Page.xaml.cs)

delegate void PageMethodDelegate(object result, object context);

4)  Our click handler is where most of the "magic" is done. (C# - Page.xaml.cs)

private void Dictionary_Click(object sender, RoutedEventArgs e)
  //Create a dictionary we wish to pass
  Dictionary<string, string> dict = new Dictionary<string, string>();
  dict.Add("test", "1");

  //get reference to PageMethods client-side object
  var pageMethods = (ScriptObject)HtmlPage.Window.GetProperty("PageMethods");

  //call PageMethod, giving delegate callbacks
  pageMethods.Invoke("TestDict", dict.ToJSDictionary<string>(), new PMDelegate(Success), new PMDelegate(Fail), "Context");

Remember that calling a page method is done in javascript by simply calling the following method signature (javascript)

PageMethods.FunctionName(arguments paramArray, successDelegate, failDelegate, context)

To clarify further, lets say we have our method on the server called Add(int x, int y).  To invoke this from the client we would use the following code (javascript)

PageMethods.Add(1, 2, successFunc, failFunc, someContext);

Note:  You do not need to write any javascript for this sample to work.  I just included the previous lines of code to give you a better understanding of what the javascript we wish to invoke looks like.

Another thing to note here is that we are creating a managed Generic Collection and adding some test data.  Since our javascript will not understand the dictionary, we need to translate it into something it will understand.  In my sample an extension method has been created and imported (ToJSDictionary).  This method has the following logic.

public static class MyExtensions
  public static object ToJSDictionary<T>(this Dictionary<string, T> dict)
    var jsdict = HtmlPage.Window.CreateInstance("Object");
    foreach (string key in dict.Keys)
      jsdict.SetProperty(key, dict[key].ToString());

    return jsdict;

Notice how we are creating a javascript object and setting each key/value pair from our generic Dictionary.

5)  The final step is to declare our callback function handlers (Success and Fail)

public void Success(object result, object context)
  ScriptObject so = result as ScriptObject;
  txt.Text = so.GetProperty("Server").ToString();

public void Fail(object result, object context)
  txt.Text = "FAIL";

Since calling out to javascript needed a conversion, it stands to reason that the translation coming in will also need to be obtained a little different.  I am not sure that it is possible to enumerate the javascript object collection, so for now, my code doesn't use another extension method to convert it to a generic dictionay, instead I go after the values directly via the GetProperty.

As I mentioned earlier, I am not certain if this is the best approach to do new development on, instead I am thinking that calling into the PageMethod directly via the Http stack that Silverlight offers will be better.  My concern here though is whether or not I can pass cookies in the same manner as calling from javascript.  Regardless, this should prove useful to those of you trying to figure out how to retrofit existing functionality into Silverlight.

This concludes the overview of how to invoke and return complex object to and from the server.  The sample provided also demonstrates the passing of simple data types (strings and integers).

Download sample application here


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