Universal Messaging Developer Guide : Web Client APIs : Web Developer's Guide for Adobe Flex : Publish / Subscribe using Datastreams and Datagroups : Managing DataGroup Membership
Managing DataGroup Membership
DataGroups are extremely lightweight from both client and server perspectives; a back-end process, such as a Complex Event Processing engine, can simply create DataGroups and then add or remove users (or even entire nested DataGroups) based on bespoke business logic. A user who is removed from one DataGroup and added to another will continue to receive events without any interruption to service, or indeed explicit awareness that any DataGroup change has occurred.
This page details some of the typical operations that DataGroup management process would carry out. Please see our Flex sample apps for more detailed examples of DataGroup management.
Tracking Changes to DataGroup Membership (DataGroupListener)
The nDataGroupListener interface is used to provide asynchronous notifications when nDataGroup membership changes occur. Each time a user (nDataStream ) or nDataGroup is added or removed from a nDataGroup, a callback will be received.

public class DataGroupListener implements nDataGroupListener
var nSession:mySession;

public function DataGroupListener(session:nSession)
mySession = session;
//add this class as a listener for all nDataGroups
//on this Universal Messaging realm
mySession.getDataGroups(this, dataGroupCallback);

//DataGroupListener Implementation
function addedGroup (to:nDataGroup, group:nDataGroup, count:int):void
//Called when a group has been added to the 'to' data group.
//count is the number of nDataStreams that will receive any events
//published to this nDataGroup

function addedStream(group:nDataGroup, stream:nDataStream, count:int):void
//Called when a new stream has been added to the data group.

function createdGroup(group:nDataGroup):void
//Called when a group has been created.

function deletedGroup(group:nDataGroup):void
//Called when a group has been deleted.

function deletedStream(group:nDataGroup, stream:nDataStream,
count:int, serverRemoved:Boolean):void
//Called when a stream has been deleted from the data group.
//serverRemoved is true if the nDataStream was removed because
//of flow control

function removedGroup(from:nDataGroup, group:nDataGroup, count:int):void
//Called when a group has been removed from the 'from' data group.

There are three ways in which the nDataGroupListener can be used:
Listening to an individual DataGroup
Listeners can be added to individual DataGroups when they are created or at any time after creation. The code snippets illustrate both approaches:

mySession.createDataGroup(dataGroupName, dataGroupCallback, dataGroupListener);

Listening to the Default DataGroup
The Default nDataGroup is a DataGroup to which all nDataStreams are added by default. If you add a DataGroupListener to the default DataGroup then callbacks will be received when:
*a nDataStream is connected / disconnected
*a nDataGroup is created or deleted
Listening to all DataGroups on a Universal Messaging Realm
The code snippet below will listen on all nDataGroups (including the default DataGroup).

mySession.getDataGroups(dataGroupsCallback, dataGroupListener);
Adding and Removing DataGroup Members
The nDataGroup class provides various methods for adding and removing nDataStreams and nDataGroups. Please see the nDataGroup API documentation for a full list of methods. Examples of some of these are provided below:

//Add a nDataStream (user) to a nDataGroup
public function addStreamToDataGroup(group:nDataGroup, user:nDataStream):void

//Remove a nDataStream (user) from a nDataGroup
public function removeStreamFromDataGroup(group:nDataGroup, user:nDataStream):void

//Add a nDataGroup to a nDataGroup
public function addNestedDataGroup(parent:nDataGroup, child:nDataGroup):void

//Remove a nDataGroup from a nDataGroup
public function removeNestedDataGroup(parent:nDataGroup, child:nDataGroup):void
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