Flex Multi-Drag

Have you ever been playing with the DragManager in your flex app and wondered  how to get more than one object dragging at once? DataGrid and List can do it, so why not other custom widgets? On a project I’ve been working on, we have a custom schedule component and want to drag multiple items around at once, so I did a little research and found out how it is done. The Flex SDK, which you can download for free, comes with source code! On my Mac, it was installed in the Flex Builder directory (/Applications/Adobe Flex Builder 3/sdks/3.2.0/frameworks/projects/framework/src/). Within there, I found what I was looking for in mx/controls/listClasses/ListBase.as

It turns out that DataGrid and List extend ListBase, which implements multi-drag for those components. If you look at the documentation for DragSource, it has an addHandler(..) method, that allows you to pass a collection along with the drag. When DragEvent.DRAG_DROP is being handled, you can pull that collection from the DragSource. Adding the objects from that collection is a manual process, but at least it is easy to pass all of the objects you’d like to drag along without much fuss. Here’s a bit of code that demonstrates this;

var dragSource: DragSource = new DragSource();
ds.addHandler(copySelectedItems, "items");
DragManager.doDrag(this, dragSource, event, dragImage, 0, 0, 0.5, dragMoveEnabled);

A really cool thing here is that “addHandler(..)” takes a method that provides the items. That method only gets called when the data is actually needed. So, you can defer data access until a drop is actually being performed. In the case where you have data to be added and just want to provide it up front, you can call “addData(..)” instead, which will take your array. The part of drag and drop that is a little more complicated with multi-drag is having a convincing looking drag proxy. If you don’t know, the drag proxy is what the user sees being moved around the screen during a drag. We’ve been creating bitmaps of the items we move instead of using the ghosted outline that is the default. When dragging multiple objects, we had to create a bunch of bitmaps and translation matricies that are used to create a bigger bitmap (which becomes the drag proxy).

To get the data in the DRAG_DROP handler, you can use some code like this;

if (event.dragSource.hasFormat("items"))
    var items:Array = event.dragSource.dataForFormat("items") as Array;

The default drag proxy is OK, but we have been creating custom bitmaps to give a nicer “drag” appearance. This got more complicated with multi-drag. The solution involves iterating through the separate drag items and creating separate bitmaps with transform matricies. Using those, and some other variables to track the bounding box for all of the items, it is possible to build a larger bitmap and paste the smaller images in (using the positional transforms). If you do this, don’t forget to apply a transform to the final drag proxy image to offset the actual click location within the larger bitmap. If you don’t your drag proxy will render with its upper left corner at the mouse, instead of where it should be.

Flash Socket Code and crossdomain Policy Serving

I’ve just spent the past day trying to get my flash app talking to another device on my network via socket 23. I found some sample telnet code (which operates on port 23) and allowed me to “talk” to the RFID reader. It worked fine as a new project in Flex Builder and being served from a local file. The moment I served the application from a web server (tomcat) on my laptop, I get crossdomain issues. Flash won’t open a socket that is different from the one that served your application unless that socket authorizes it. I will spare you the details that took many hours of my day. If you’re trying to talk to another web server on a different port, no problem.. just put the crossdomain.xml file on that server that authorizes the connection. In this case, I was trying to connect to another host and another port (which runs telnet, not http). The RFID reader can’t be modified to serve up a crossdomain.xml file, so I had to get creative.

My solution was to run a TCP proxy on my web server machine that proxied requests to the RFID reader. I made it listen on port 8023 and forward requests to 23 on the RFID reader. This was the start because I still got errors about that localhost:8023  not being authorized. It turns out that when you try the connection, flash connects to the socket and sends 23 bytes which contain “<policy-file-request/>”. Flash expects whatever is running at that port to respond with the policy string (that would have been in the crossdomain.xml file). So, I modified this little proxy class I got off the internet to recognize the proxy request and respond with a proxy string (null terminated.. that is very important!). Once I had this set up right, I was able to communicate from my flash app to my RFID reader. Not the most elegant solution, but this is something temporary for a demo.


To run the code below, compile with javac and invoke “java -classpath <class.file.location> ProxyThread 8023 23″. Those options are what I used to talk to my RFID reader, but you’ll likely use different values.

import java.net.*;
import java.io.*;
  Java Transparent Proxy
  Copyright (C) 1999 by Didier Frick (http://www.dfr.ch/)
  This software is provided under the GNU general public license (http://www.gnu.org/copyleft/gpl.html).

public class ProxyThread extends Thread {
     protected class StreamCopyThread extends Thread {
	private Socket inSock;
	private Socket outSock;
	private boolean done=false;
	private StreamCopyThread peer;
	private boolean inFromLocal;	// in from local port
	private OutputStream out;
	private String policy = "<cross-domain-policy>\n<allow-access-from domain=\"*\" to-ports=\"8023\"/>\n</cross-domain-policy>";
	public StreamCopyThread(Socket inSock, Socket outSock, boolean in) {
	    this.inFromLocal = in;
	public void sendPolicy() {
		try {
			System.err.println("Sent policy");
		} catch (IOException ex) {
			System.err.println("Error sending policy file");
	public void run() {
	    byte[] buf=new byte[bufSize];
	    int count=-1;
	    try {
		InputStream in=inSock.getInputStream();
		try {
		    while(((count=in.read(buf))>0)&&!isInterrupted()) {
		    	if (inFromLocal && count==23 && new String(buf).startsWith("<policy-file-request/>")) {
				// send policy file back.. don't forward this to other port
				System.err.println("Got policy request");
			else {
				//System.err.println(count+" bytes "+(inFromLocal?"sent":"received"));
		} catch(Exception xc) {
		    if(debug) {
			// FIXME
			// It's very difficult to sort out between "normal"
			// exceptions (occuring when one end closes the connection
			// normally), and "exceptional" exceptions (when something
			// really goes wrong)
			// Therefore we only log exceptions occuring here if the debug flag
			// is true, in order to avoid cluttering up the log.
		} finally {
		    // The input and output streams will be closed when the sockets themselves
		    // are closed.
	    } catch(Exception xc) {
	    synchronized(lock) {
		try {
		    if((peer==null)||peer.isDone()) {
			// Cleanup if there is only one peer OR
			// if _both_ peers are done
			// Signal the peer (if any) that we're done on this side of the connection
		} catch(Exception xc) {
		} finally {
	public boolean isDone() {
	    return done;
	public void setPeer(StreamCopyThread peer) {

    // Holds all the currently active StreamCopyThreads
    private java.util.Vector connections=new java.util.Vector();
    // Used to synchronize the connection-handling threads with this thread
    private Object lock=new Object();
    // The address to forward connections to
    private InetAddress dstAddr;
    // The port to forward connections to
    private int dstPort;
    // Backlog parameter used when creating the ServerSocket
    protected static final int backLog=100;
    // Timeout waiting for a StreamCopyThread to finish
    public static final int threadTimeout=2000; //ms
    // Linger time
    public static final int lingerTime=180; //seconds (?)
    // Size of receive buffer
    public static final int bufSize=2048;
    // Header to prepend to log messages
    private String header;
    // This proxy's server socket
    private ServerSocket srvSock;
    // Debug flag
    private boolean debug=false;
    // Log streams for output and error messages
    private PrintStream out;
    private PrintStream err;
    private static final String 
	argsMessage="Arguments: ( [source_address] source_port dest_address dest_port ) | config_file";
    private static final String 

    public ProxyThread(InetAddress srcAddr,int srcPort,
		       InetAddress dstAddr,int dstPort, PrintStream out, PrintStream err) 
	throws IOException {
	this.srvSock=(srcAddr==null) ? new ServerSocket(srcPort,backLog) :  
	    new ServerSocket(srcPort,backLog,srcAddr);
	this.header=(srcAddr==null ? "" : srcAddr.toString())+":"+srcPort+" <-> "+dstAddr+":"+dstPort;
    public void run() {
	out.println(header+" : starting");
	try {
	    while(!isInterrupted()) {
		Socket serverSocket=srvSock.accept();
		try {
		    Socket clientSocket=new Socket(dstAddr,dstPort);
		    StreamCopyThread sToC=new StreamCopyThread(serverSocket,clientSocket, true);
		    StreamCopyThread cToS=new StreamCopyThread(clientSocket,serverSocket, false);
		    synchronized(lock) {
		} catch(Exception xc) {
	} catch(IOException xc) {
	} finally {
	    out.println(header+" : stopped");
     private void cleanup() {
	synchronized(lock) {
	    try {
		while(connections.size()>0) {
		    StreamCopyThread sct=(StreamCopyThread)connections.elementAt(0);
	    } catch(InterruptedException xc) {
    private static ProxyThread addProxy(String src,String srcPort, String dst, String dstPort,
					PrintStream out, PrintStream err) throws
					UnknownHostException, IOException
	InetAddress srcAddr=(src==null) ? null : InetAddress.getByName(src);
	return new ProxyThread(srcAddr,Integer.parseInt(srcPort),
    private static java.util.Vector parseConfigFile(String fileName,PrintStream out,PrintStream err) throws 
        FileNotFoundException, IOException, UnknownHostException
	java.util.Vector result=new java.util.Vector();
	FileInputStream in=new FileInputStream(fileName);
	java.util.Properties props= new java.util.Properties();
	for(int i=0;;i++) {
	    String srcAddr=props.getProperty(propertyPrefix+"."+i+".sourceAddr");
	    String srcPort=props.getProperty(propertyPrefix+"."+i+".sourcePort");
	    String dstAddr=props.getProperty(propertyPrefix+"."+i+".destAddr");
	    String dstPort=props.getProperty(propertyPrefix+"."+i+".destPort");
	    if(dstAddr==null) {
		throw new IllegalArgumentException("Missing destination address for proxy "+i);
	    if(dstPort==null) {
		throw new IllegalArgumentException("Missing destination port for proxy "+i);
	return result;
    static java.util.Vector parseArguments(String[] argv,PrintStream out,PrintStream err) throws
        FileNotFoundException, IOException, UnknownHostException
	java.util.Vector result=null;
	int argBase=0;
	String src=null;
	if(argv.length>1) {
	    if(argv.length>3) {
	    result=new java.util.Vector();
	} else if(argv.length==1) {
	} else {
	    throw new IllegalArgumentException(argsMessage);
	return result;
    public static void main(String[] argv) throws Exception {
	System.out.println("Java Transparent Proxy");
	System.out.println("Copyright (C) 1999 by Didier Frick (http://www.dfr.ch/)");
	System.out.println("This software is provided under the GNU general public license"+
			   " (http://www.gnu.org/copyleft/gpl.html)");
	try {
	} catch(IllegalArgumentException xc) {
The initial ProxyThread code came from here: http://www.dfr.ch/en/proxy.html