Programming Flash Communication Server

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Chapter 3: Managing Connections

to them. In both cases, the NetConnection object should be one that has attempted to

make a connection even if the connection is not yet established. For example the pro-

cess of sending data can be started via a NetStream.send( ) or SharedObject.send( )

method call before a connection is established. The data is held in a queue until the

connection is made. Similarly, a NetStream object can start the process of publishing

or playing audio or video before a connection is made. In this case, when the connec-

tion is made, the stream will begin to publish or play.

The important exception to this is shared object data and the shared object onSync( )

handler described in Chapter 8. As an added convenience, if onStatus( ) handlers are

not created for SharedObject and NetStream objects, the onStatus( ) handler of the

NetConnection with which they are associated will be called and passed the

SharedObject and NetStream information objects. In some cases, especially when

data is sent, these conveniences are useful, but for the most part should be avoided.

It is often easier to manage an application and provide better information to the user

if objects that depend on a network connection define their own onStatus( ) event

handlers and do nothing until a connection is successfully made.

Reusing a NetConnection Object

Often a Flash movie must connect to more than one application instance. A familiar

example is when Flash must first connect to a lobby so the user can select a chat

room to visit. In this case, the lobby may be one application and the chat rooms may

be implemented by another application. The lobby connection can be closed and

then a new NetConnection object, with a different onStatus( ) method, can be cre-

ated to connect to the chat application. Instead of creating a new NetConnection

object, the Flash movie can reuse an existing one. In theory, you can disconnect from

one application and connect to another by calling the connect( ) method with a new

target URI. When this happens, the old connection is closed and a new one is

attempted. However, two other things should normally happen. First, before a con-

nection is closed, you should perform any required cleanup, such as closing objects

and components that depend on the connection. Second, you must perform any pre-

paratory work—at minimum you’ll usually put in place a different onStatus( ) han-

dler—before connecting to the next application.

To follow through with the previous example, suppose an additional application,

named testChat, is available and that once the user is in the lobby he can click a but-

ton to visit a testChat instance named

room1. In this case, the main timeline of the

movie would require separate

Login, Lobby, and ChatRoom frames as illustrated in

Figure 3-2.

The Chat button would be placed in the

Lobby frames, and a Lobby button would be

placed within the

ChatRoom frames. Example 3-4 shows the onChat( ) function that

would be called when the Chat button is clicked.

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Reusing a NetConnection Object

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In Example 3-4, event handling of close and connection error messages is turned off

so that the playhead is not sent back to the

Login frame when Flash calls lobbyChat_

nc.close( ). The example assigns a new onStatus( ) handler, named ChatRoom_

onStatus( ), to the

lobbyChat_nc object as follows:

lobbyChat_nc.onStatus = ChatRoom_onStatus;

Finally, when the connection is attempted, two global variables, userName and

password, are used to retrieve the username and password to submit, because the text

fields are no longer on the Stage when the user is in the lobby. Example 3-5 shows

the code for the ChatRoom_onStatus( ) function. It is used as the new onStatus( )

handler for the

lobbyChat_mc object, as indicated in the preceding code.

Figure 3-2. The timeline with Login, Lobby, and ChatRoom states

Example 3-4. Connecting from the lobby to a chat room

function doChat (btn) {

// Don't process the next close message.

lobbyChat_nc.handleCloseEvents = false;

// Close the connection to the lobby.

lobbyChat_nc.close( );

// Set the onStatus( ) handler, defined in Example 3-5.

lobbyChat_nc.onStatus = ChatRoom_onStatus;

// Make sure events are handled by it.

lobbyChat_nc.handleCloseEvents = true;

// Try to connect to a chat room.

if (lobbyChat_nc.connect("rtmp:/testChat/room1", userName, password)) {

writeln("Please wait. Attempting chat room connection...");

}

else {

writeln("Can't attempt connection. Is the URI correct?");

}

}

Example 3-5. The chat room onStatus( ) handler

function ChatRoom_onStatus (info) {

// Always deal with successful connections.

if (info.code == "NetConnection.Connect.Success") {

this.handleCloseEvents = true;

writeln("Success, you are connected to a chat room!");