getRoster -> PacketListener doesn't work.

hi All.i use aSmack.

Roster roster = tcpConnection.getRoster(); 
tcpConnection.addPacketListener(new PacketListener() {                                            
tcpConnection.addPacketListener(new PacketListener() {
@Override     publicvoid processPacket(Packet packet) {          System.out.println("processPacket->" + packet.toXML());     }}, new PacketFilter() {     @Override     publicboolean accept(Packet packet) {          System.out.println("accept->" + packet.toXML());          returnfalse;}});   

but packet listener doesn't work before&after getRoster.it's blocked packet listener.

please help me