聊天消息发送不成功

聊天过程中偶尔会出现不能发送消息的情况，但是网络正常并且收到别人发来的聊天消息也是正常的。
查看log之后发现，sendMessage方**报：java.lang.IllegalStateException: Not connected to server.的错误。并且答应了如下log
04-09 13:32:54.420 4045-6045/com.dingphone.plato W/**.err﹕ java.lang.IllegalStateException: Not connected to server.
04-09 13:32:54.420 4045-6045/com.dingphone.plato W/**.err﹕ at org.jivesoftware.smack.XMPPConnection.sendPacket(Unknown Source)
04-09 13:32:54.420 4045-6045/com.dingphone.plato W/**.err﹕ at org.jivesoftware.smack.ChatManager.sendMessage(Unknown Source)
04-09 13:32:54.420 4045-6045/com.dingphone.plato W/**.err﹕ at org.jivesoftware.smack.Chat.sendMessage(Unknown Source)
04-09 13:32:54.420 4045-6045/com.dingphone.plato W/**.err﹕ at com.easemob.chat.SendMessageThread.sendMessageXmpp(Unknown Source)
04-09 13:32:54.420 4045-6045/com.dingphone.plato W/**.err﹕ at com.easemob.chat.SendMessageThread.run(Unknown Source)
04-09 13:32:54.420 4045-6045/com.dingphone.plato W/**.err﹕ at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
04-09 13:32:54.420 4045-6045/com.dingphone.plato W/**.err﹕ at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
04-09 13:32:54.420 4045-6045/com.dingphone.plato W/**.err﹕ at java.lang.Thread.run(Thread.java:841)


一旦出现这种情况，只能通过退出应用再重新启动来恢复。请问我能怎么避免这种情况的发生？或者一旦出现这种情况怎么让客户端恢复正常状态？

使用的环信SDK：2.1.5