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Generating events under COM+ When you exit, the wizard creates a project containing a type library that defines your event object and its interface. Use the Type Library editor to define the methods of that interface. These methods are the event handlers that clients implement to respond to events. The Event object project includes the project file, _ATL unit to import the ATL template classes, and the _TLB unit to define the type library information. It does not include an implementation unit, however, because COM+ event objects have no implementation. The implementation of the interface is the responsibility of the client. When your server object calls a COM+ event object, COM+ intercepts the call and dispatches it to registered clients. Because COM+ event objects require no implementation object, all you need to do after defining the object’s interface in the Type Library editor is compile the project and install it with COM+ COM+ places certain restrictions on the interfaces of event objects. The interface you define in the Type Library editor for your event object must obey the following rules: • • • • The event object’s interface must derive from IDispatch. All method names must be unique across all interfaces of the event object. All methods on the event object’s interface must return an HRESULT value. The modifier for all parameters of methods must be blank. Using the COM+ Event Subscription object wizard You can create the subscriber component using Delphi’s COM+ Subscription Object wizard. To bring up the wizard, 1 Choose File|New|Other. 2 Select the tab labeled ActiveX. 3 Double-click the COM+ Subscription Object icon. In the wizard dialog, enter the name of the class that will implement the event interface. Choose the threading model from the combo box. In the Interface field, you can type the name of your event interface, or click on the Browse button to bring up a list of all event classes currently installed in the COM+ Catalog. The COM+ Event Interface Selection dialog also contains a browse button. You can use this button to search for and select a type library containing the event interface. When you select an existing event class (or type library), the wizard will give you the option of automatically implementing the interface supported by that event class. If you check the Implement Existing Interface checkbox, the wizard will automatically stub out each method in the interface for you. To complete the wizard, enter a brief description of your event subscriber component, and click on OK. 46-22 Developer’s Guide
