MSDN Magazine - November 2008 - (Page 36)

} } return g.ToString(); The ScriptableMember attribute on public methods of a scriptable class indicates that the method can be invoked from JavaScript. If all public methods of a class are scriptable, you can use the ScriptableType attribute on the class to automatically extend the scriptability attribute to all public methods. An object registered as scriptable is instantiated through managed code and an existing instance is passed down to JavaScript. Not all managed types can be directly instantiated in JavaScript. Before you can create an instance of a managed class from JavaScript, you first need to register the type you want as available for creation from JavaScript code: HtmlPage.RegisterCreateableType("StockPicker", typeof(Samples.Order)); you can only use as the factory a scriptable type that has a scriptable member that requires that type. In other words, if Customer is registered as scriptable and method Add is scriptable, then you can instantiate Order from JavaScript without declaring the type creatable. The following code would work: var customer = $get("Silverlight1").content.Customer; var order = customer.createManagedObject("Order"); order.ID = 1; o.OrderDate = new Date(); customer.Add(order); The first argument indicates the alias for the type to be used from within JavaScript. Here’s how you create an instance of the Samples.StockPicker class: var plugin = $get("Silverlight1"); var type = "Samples.StockPicker"; var inst = plugin.content.services.createObject(type); Managed types are marshaled down to JavaScript wrapped as browser objects. The wrapper browser object contains a table of valid methods to call from JavaScript. The list includes all methods declared as scriptable, plus createManagedObject. Invocations on methods are then resolved by invoking the corresponding method in the managed code. Cross-Domain Access and Silverlight Plug-Ins You retrieve the Silverlight plug-in, access the content.services property and then invoke the method createObject. The argument to createObject is the string with the name of the managed type to instantiate. A scriptable type that has complex and custom types in the signatures of its methods also works as a factory for its types. For example, imagine a managed type Customer with the following method: void Add(Order order); What about the Order type? Should it be declared createable? Not necessarily. If you omit the call to RegisterCreateableType, then Figure 6 A Sample Manifest File for a Silverlight 2 App Figure 7 Exposure to Another Silverlight Plug-In A Silverlight application that exposes a public managed API is subject to cross-domain access. If cross-domain access represents a security hazard, or just an unwanted feature, you should take your countermeasures. When a page with a Silverlight plug-in is hosted in a frame, it is possible that the host page lives in a different domain than the Silverlight application. This means that the JavaScript code in the host page (cross-domain) is able to gain access through the frame to the Silverlight plug-in and script any public-managed object. Cross-domain access to the Silverlight content may be disabled, fully enabled, or limited to scripting. It is disabled by default. You can control cross-domain access, as in Figure 6, by using the ExternalCallersFromCrossDomain attribute in the Deployment node of the Silverlight application manifest file. The manifest file is the file that is generated by Visual Studio 2008 when you compile a Silverlight project. When you load a page in the browser that contains one or more Silverlight plug-ins, you still get one instance of the CLR per browser process. However, each running instance of the Silverlight plug-in gets its own AppDomain. Nothing is being shared between plugins and communication is possible, but only through code—and with the help of a little trick. The trick consists essentially of using the browser interoperability layer as an intermediary. One plug-in exposes a managed interface and the other connects to it and invokes methods. So one plug-in defines a few scriptable members, like so: public partial class Page : UserControl { public Page() { InitializeComponent(); HtmlPage.RegisterScriptableObject( "Action", new ActionPageCommand()); } } The ActionPageCommand class contains all methods that the plugin exposes for external callers. Here’s an example: [ScriptableType] public class ActionPageCommand { public int GetRandomNumber() 36 msdn magazine Cutting Edge

Table of Contents Feed for the Digital Edition of MSDN Magazine - November 2008

Contents MSDN Magazine - November 2008 Toolbox CLR Inside Out Data Points Cutting Edge Security Briefs Test Your Security IQ Agile SDL Access Control Utility Spotlight RIA Test Run Wicked Code Foundations Team System End Bracket

MSDN Magazine - November 2008

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