IMessaging.RegisterNotification()

Description:

The RegisterNotification method registers the widget to receive notifications of new incoming messages. For each new message, the method returns the header information of that message.

This is an asynchronous method.

Syntax:

result = so.IMessaging.RegisterNotification(criteria, callback);

Arguments:

criteria:

This is an object that specifies the request for notification of new messages. The object must contain the Type property (string), and this property must contain the value "NewMessage":
```
criteria.Type = "NewMessage";
```
callback:

The callback argument is the name of the method that is executed when RegisterNotification has results or status information to return. You must define this method separately. Follow the instructions in section Defining the callback handler for an asynchronous method to define the callback method.

Return value:

The RegisterNotification method returns an object that contains the initial return value for the asynchronous call it started (see the following table). The actual notification information is returned by the callback method in the ReturnValue property of its result object. The returned information is described in section Returned notification information.

**Table:** Return value properties for RegisterNotification
Property	Description	Value
`result.TransactionID`	This is a number used as an identification to match transactions started with a `RegisterNotification` call to one or more calls it generates to `callback`.
`result.ErrorCode`	This is a number that specifies a predefined error code.	See Service API error codes.
`result.ErrorMessage`	This is a text string that describes the error.	See Messaging Service API error messages.

Remarks:

RegisterNotification retrieves new message updates until cancelled with CancelNotification (or Cancel). You can therefore have only one RegisterNotification call (one instance) pending or in use at any given time.

Example code:

For the complete source of a sample widget that demonstrates how to use this Service API, see the full example.