Flex 3 tracking users (their presence) in the flash app

i have a simple chat application in flex 3 and i want to开发者_StackOverflow社区 make the list of users present on the right, how track this, how do you know when a user left if he just closed the browser window or typed in an other url ?

You could maintain a presence list on the server, and have each client periodically let the server know that they are still online when they are logged in. Then each client could query the server periodically to obtain a list of all the online users. The polling rates could be adjusted to suit your individual application needs.