MSDN Magazine - July 2008 - (Page 18)

I use the first line, AddInStore.Update, to method implementation). I will explain search for available add-ins and pipeline the significance of this later. components. PipelineStoreLocation.ApFigure 4 shows what the host view plicationBase tells it to look in the applilooks like for the ShapeApplication obcation’s folder. For a detailed description ject. The types used in members can eiof the folder structure, see go.microsoft.com/ ther be built-in framework types, such as fwlink/?LinkId=117521. Next, I get the type of EventHandler , or other views, such the add-ins I want to activate. In this case as IDrawing. You can download FxCop it’s the IShapeAddIn type defined in the rules from our CodePlex site at go.micro soft.com/fwlink/?LinkId=117524 to verify that host views assembly. Finally, I call AddInStore.FindAddIns, which returns a Figure 3 The Add-In Manager Form the views are easily adaptable into a comcollection of available add-in tokens that plete pipeline. I can inspect and activate. Once I have selected a token from the Once I have created the views assembly, I modify the host’s classcollection, I can use one line of code to activate it: es to inherit from corresponding views. The changes to the Shape// activate the add-in in full trust mode Application class are shown here in red: ShapeAppHostViews.IShapeAddIn addIn = token.Activate ( AddInSecurityLevel.FullTrust); I can also choose to activate add-ins out of process or under a different trust level. For a list of isolation levels, you can go to go.microsoft.com/fwlink/?LinkId=117522. For a performance comparison of isolation levels, see the blog post on performance, available at go.microsoft.com/fwlink/?LinkId=117523. public class ShapeApplication : System.Windows.Forms.IWin32Window { } public class ShapeApplication : ShapeAppHostViews.IShapeApplication, System.Windows.Forms.IWin32Window { } Exposing the Object Model Once the empty pipeline and add-in manager are in place, I can start exposing functionality from the host to the add-in. To expose the types included in the object model, I need to first create a host view in the HostViews assembly for each type that I want to expose. I can expose properties, methods, and events in the view. The host view can be either an abstract base class or an interface. In the ShapeApp, I have used interfaces for three reasons. First, they are needed for events to work correctly when used from Visual Basic®. Second, C# does not support multiple inheritance, so a class cannot inherit from two base classes. Therefore, the view should be an interface to allow all host classes to implement it (even if they already have a base). Third, interfaces allow EIMI (explicit interface Figure 4 ShapeApplication Object Host View namespace ShapeAppHostViews { public interface IShapeApplication { // the drawing present in the selected tab IDrawing ActiveDrawing { get; } // a collection of available shapes (square, circle, etc) IShapeCollection AvailableShapes { get; } // a collection of drawings currently open in the application IDrawingCollection Drawings { get; } // main window visibility bool Visible { get; set; } // create a new drawing in the application IDrawing NewDrawing(); // completely exit the application void Quit(); // event fired when a drawing is created event EventHandler CreatedDrawing; Next, I need to implement each member from the host view. For members that use built-in types as arguments and return values, there is no special implementation required (other than ensuring the member is public in the host’s class). For example, the Visible property in the ShapeApplication class has the same signature as the Visible interface member: public bool Visible { get { } set { } } This means that the existing implementation of Visible in the host’s ShapeApplication class will be used as the view implementation. However, members that use other types defined in the host views need to be implemented explicitly. For example, the ActiveDrawing property has different signatures in the ShapeApplication class and in the IShapeApplication host view. The original version in the host’s class returns a Drawing object: public Drawing ActiveDrawing { get { } } The version in the host view, IShapeApplication, can only return the corresponding view, IDrawing: IDrawing ActiveDrawing { get; } } } To implement the second version in the host’s class, I need to use EIMI. I do this by adding a new property in the host’s class with the same name, ActiveDrawing. Now the host’s ShapeApplication class has two properties called ActiveDrawing (see Figure 5). The new implementation implicitly casts the Drawing object to the IDrawing type. If you are exposing an object model for a Windows Forms application, it is likely that some of the exposed CLR Inside Out 18 msdn magazine http://go.microsoft.com/fwlink/?LinkId=117521 http://go.microsoft.com/fwlink/?LinkId=117521 http://go.microsoft.com/fwlink/?LinkId=117524 http://go.microsoft.com/fwlink/?LinkId=117524 http://go.microsoft.com/fwlink/?LinkId=117522 http://go.microsoft.com/fwlink/?LinkId=117523

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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