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Objects in the Outlook PIA

When browsing the Outlook Primary Interop Assembly (PIA) in an object browser, you may notice that many interfaces and classes have names referencing familiar objects in the Outlook object model. Some objects in the object model have a one-to-one mapping to interfaces in the PIA. For example, the AddressEntry is mapped to the AddressEntry interface and the AddressList object is mapped to the AddressList interface in the PIA. However, most other objects have a one-to-many mapping in the PIA. This one-to-many mapping applies to some objects that existed before Microsoft Office Outlook 2007, and all objects added since Outlook 2007. This topic lists the typical .NET interfaces, classes, and delegates that are mapped to a COM object and describes how to access an object in the Outlook PIA. It also describes a few exceptions in the Outlook PIA where the objects are hidden or deprecated in the COM-based object model.

This section illustrates the typical helper classes for an object in the Outlook PIA by using the FormRegion object as an example. The FormRegion object was added to the object model in Outlook 2007. Related to the FormRegion object in the PIA are the interfaces, classes, and delegates, illustrated in Figure 1.

Figure 1. The FormRegion object represented in the Outlook object model and in the Outlook PIA

Diagram of the FormRegion object

The one interface that you most often use to access the FormRegion object and its method, property, and event members is the FormRegion interface. However, you should not consider the FormRegion .NET interface as an exact mirror image of the FormRegion COM object; if you look at the Object Browser in Visual Studio, you will find that the FormRegion interface inherits from another interface, the _FormRegion interface. In fact, the FormRegion interface is just one of the few interfaces and classes that result from creating the Outlook PIA based on the COM type library.

To create the Outlook PIA, Outlook uses the Type Library Importer (TLBIMP) in the .NET Framework to convert type definitions in the COM type library into equivalent definitions in a Common Language Runtime assembly. In COM, the FormRegion object is actually a coclass that consists of the following two interfaces defining the interfaces that the FormRegion object implements:

TLBIMP directly imports _FormRegion and FormRegionEvents from the type library.

Other than importing the primary interface and event interface, TLBIMP creates a .NET interface that has the same name as the COM object, and a .NET class that uses the name of the object and appends it with "Class". In the case of the FormRegion object, TLBIMP creates the following:

Of the .NET interfaces and .NET class mentioned in this topic, you always use the .NET interface that TLBIMP creates to access an object. For example, to access a FormRegion object in VB, you always use the FormRegion interface, as in the following code example:

using Outlook = Microsoft.Office.Interop.Outlook; 
void DemoFormRegion(Outlook.FormRegion region) 
    Outlook.FormRegion myFormRegion = region; 
    // Additional method code here

For information about the purpose of the primary interface and the .NET class that TLBIMP imports and creates respectively, see Methods and Properties in the Outlook PIA. For information about the purpose of the event-related interfaces, delegates, and sink helper classes, see Events in the Outlook PIA.

Objects deprecated in the type library are exposed in the Outlook PIA. For example, the _DDocSiteControl and _DRecipientControl objects are hidden in the type library but are exposed in the PIA.

Another example of a deprecated object is the MAPIFolder object. Starting in Outlook 2007, the Folder object has replaced the MAPIFolder object in the object model. Existing solutions should replace references to MAPIFolder by Folder, and all solutions new for Outlook 2007 and after should use only the Folder object. For unmanaged solutions, the Object Browser of the Visual Basic Editor no longer lists the MAPIFolder object, not even as a hidden object. For managed solutions, even though the Outlook PIA exposes a Folder interface through which you access the Folder object and its members, the Outlook PIA also exposes MAPIFolder as an interface that defines the members of the Folder object.

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