MSDN Magazine - July 2008 - (Page 20)

Figure 7 Pipeline Components Required Host-Side Objects Host (object lives here) Host view View-to-contract host adapter Contract Contract-to-view add-in adapter Add-in view Add-in (object is accessed here) Add-In-Side Objects Add-in (object lives here) Add-in view View-to-contract add-in adapter Contract Contract-to-view host adapter Host view Host (object is accessed here) public interface IShapeApplicationContract : IContract { void CreatedDrawingAdd(ICreatedDrawingEventHandlerContract handler); void CreatedDrawingRemove(ICreatedDrawingEventHandlerContract handler); } public interface ICreatedDrawingEventHandlerContract : IContract { void Handler(ICreatedDrawingEventArgsContract args); } You can see that I have created a new contract for the event handler, ICreatedDrawingEventHandlerContract, because delegates the functionality from the host one bit at a time, compile it, and test like System.EventHandler cannot it. This iterative approach helps avoid a seemingly endless string of be used in a contract. compile errors. Of course, once the interfaces have been finalized The add-in-side adapter registers a handler on the host side and the application is released, I can’t add any more methods to through the Add and Remove methods, and it maintains a local the existing interfaces. What adapters I’ll need depends on where event that the add-in can subscribe to. The host-side adapter calls an object lives and where it is accessed. Generally, objects can fall the Handler function when the event is fired. into one of the following three categories: This added complexity is mostly transparent to the add-in deHost-Side Objects These objects live on the host side and are ac- veloper, except for one caveat: the add-in must register and unregcessed from the add-in (for example, the ShapeApplication class). ister itself on the same adapter instance of an object. Otherwise, To expose them to the add-in, I need the unregistering will not work. pipeline components shown in Figure 7. Next, I will describe how a host obSince the object exists on the host side, I ject is able to have two (or more) sets of start from the host view on the top. I use a adapter objects that reference it. When view-to-contract host adapter to convert an object on the host side is returned to it to a contract, and contract-to-view addthe add-in (through a property access or in adapter to convert it to the add-in view. function call), two adapter objects (hostThese two adapters let the add-in access side adapter and add-in-side adapter) are the host-side object. created that allow access to the host obAdd-In-Side Objects These objects live ject. When the same object is returned on the add-in side and are accessed from again to the add-in, two new adapters the host (for example, the ShapeAddIn are created. class). The pipeline components are simFor example, accessing ShapeApilar here, but the direction of the adapt- Figure 8 Collaboration Add-In UI plication.ActiveDrawing twice will ers is reversed to allow the host access to return two different object referencthe add-in-side object. The view-to-contract adapter is now on es to the add-in, and ShapeApplication.ActiveDrawing.Rethe add-in side instead of the host side, and the contract-to-view ferenceEquals(ShapeApplication.ActiveDrawing) will return false. adapter is now on the host side. Note that the rest of the pipeline The presence of two (or more) adapters for the same host object (the views and the contract) is identical. can be a problem when registering/unregistering events and storEither-Side Objects These are objects that can live on either side ing host objects in collections, among other things. and can be accessed from either side. These require four adapters, To help solve these problems, the .Equals and .GetHashCode two for each side, since I need to adapt them either way. Note that if functions can be overridden on the adapters to call the correyou’re using the same assembly for the host and add-in view, you can sponding functions on the real host object. This allows us to put re-use adapters as well. In that case you would need only two. host objects into collections in the add-in, and methods like .ConContracts do not support events natively. However, events can tains work fine. Of course, it’s also true that the add-in developer be simulated in contracts by using the following pattern (example still has to ensure that events are registered and unregistered on shown from the IShapeApplication.CreatedDrawing event): the same object. And you should know that the .Equals function Host views: can help with this. As you may have guessed, another option is to cache adapters. public interface IShapeApplication However, this is difficult in practice, because there is no easy way { to store a weak mapping of objects to adapters (here, weak refers // event fired when a drawing is created to weak object references, which the garbage collector ignores). event EventHandler CreatedDrawing; } Using a regular dictionary will prevent adapters and objects from Corresponding contracts: being garbage collected. 20 msdn magazine CLR Inside Out

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

MSDN Magazine - July 2008 Contents Toolbox CLR Inside Out Flex Your Data Data Points Advanced Basics Office Space Cutting Edge Data Services ADO.NET Data and WPF Transactions WCF P2P Test Run Security Briefs Foundations .NET Matters {End Bracket}

MSDN Magazine - July 2008

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