我正在按照这里http://dalelane.co.uk/blog/?p=1599的Dale Lane MQTT Android样例实现项目，这个样例对于我的特定目的工作得很好，但我面临一个无法解决的问题。
经过广泛测试，我发现当手机完全失去连接后，该服务不会重新连接。例如，如果将手机放入飞行模式，然后退出飞行模式，该服务将继续尝试connectToBroker()，但永远不会连接。
如果我在主屏幕上按下“connect”按钮并使用给定的主机/主题参数启动服务，则应用程序可以正确连接。
我该如何解决这个问题？应用程序在WIFI网络与手机数据之间切换时没有问题。
经过广泛测试，我发现当手机完全失去连接后，该服务不会重新连接。例如，如果将手机放入飞行模式，然后退出飞行模式，该服务将继续尝试connectToBroker()，但永远不会连接。
如果我在主屏幕上按下“connect”按钮并使用给定的主机/主题参数启动服务，则应用程序可以正确连接。
我该如何解决这个问题？应用程序在WIFI网络与手机数据之间切换时没有问题。
02-16 12:19:39.348: E/mqtt(23628): ping failed - MQTT exception
02-16 12:19:39.348: E/mqtt(23628): com.ibm.mqtt.MqttNotConnectedException
02-16 12:19:39.348: E/mqtt(23628): at com.ibm.mqtt.Mqtt.writePacket(Unknown Source)
02-16 12:19:39.348: E/mqtt(23628): at com.ibm.mqtt.Mqtt.pingOut(Unknown Source)
02-16 12:19:39.348: E/mqtt(23628): at com.ibm.mqtt.MqttClient.ping(Unknown Source)
02-16 12:19:39.348: E/mqtt(23628): at com.limosys.limosystestmqtt.MQTTService$PingSender.onReceive(MQTTService.java:919)
02-16 12:19:39.348: E/mqtt(23628): at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:778)
02-16 12:19:39.348: E/mqtt(23628): at android.os.Handler.handleCallback(Handler.java:733)
02-16 12:19:39.348: E/mqtt(23628): at android.os.Handler.dispatchMessage(Handler.java:95)
02-16 12:19:39.348: E/mqtt(23628): at android.os.Looper.loop(Looper.java:136)
02-16 12:19:39.348: E/mqtt(23628): at android.app.ActivityThread.main(ActivityThread.java:5105)
02-16 12:19:39.348: E/mqtt(23628): at java.lang.reflect.Method.invokeNative(Native Method)
02-16 12:19:39.348: E/mqtt(23628): at java.lang.reflect.Method.invoke(Method.java:515)
02-16 12:19:39.348: E/mqtt(23628): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:792)
02-16 12:19:39.348: E/mqtt(23628): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:608)
02-16 12:19:39.348: E/mqtt(23628): at dalvik.system.NativeStart.main(Native Method)
以下是ping失败时抛出的异常的堆栈跟踪，应用程序将根据给定的keepAliveSecond值每隔10秒尝试重新连接。
连接丢失（CONNECTIONLOST）
/*
* callback - method called when we no longer have a connection to the message broker server
*/
public void connectionLost() throws Exception {
// we protect against the phone switching off while we're doing this
// by requesting a wake lock - we request the minimum possible wake
// lock - just enough to keep the CPU running until we've finished
PowerManager pm = (PowerManager) getSystemService(POWER_SERVICE);
WakeLock wl = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "MQTT");
wl.acquire();
//
// have we lost our data connection?
//
if (isOnline() == false) {
Log.e("CONNECTION LOST", "LOST CONNECTION");
connectionStatus = MQTTConnectionStatus.NOTCONNECTED_WAITINGFORINTERNET;
// inform the app that we are not connected any more
broadcastServiceStatus("Connection lost - no network connection");
//
// inform the user (for times when the Activity UI isn't running)
// that we are no longer able to receive messages
notifyUser("Connection lost - no network connection", "MQTT",
"Connection lost - no network connection");
//
// wait until the phone has a network connection again, when we
// the network connection receiver will fire, and attempt another
// connection to the broker
} else {
//
// we are still online
// the most likely reason for this connectionLost is that we've
// switched from wifi to cell, or vice versa
// so we try to reconnect immediately
//
connectionStatus = MQTTConnectionStatus.NOTCONNECTED_UNKNOWNREASON;
// inform the app that we are not connected any more, and are
// attempting to reconnect
broadcastServiceStatus("Connection lost - reconnecting...");
// try to reconnect
if (connectToBroker()) {
subscribeToTopic(topicName);
}
}
// we're finished - if the phone is switched off, it's okay for the CPU
// to sleep now
wl.release();
}
连接到代理 此代码在服务可用后（即退出飞行模式并连接到4G / Wifi）多次调用。
/*
* (Re-)connect to the message broker
*/
private boolean connectToBroker() {
try {
// try to connect
Log.e("CONNECTTOBROKER", "TRYING TO CONNECT");
Log.e("SERVICE HOST - CONNECT TO BROKER", "" + brokerHostName);
Log.e("SERVICE TOPIC - CONNECT TO BROKER", "" + topicName);
mqttClient.connect(generateClientId(), cleanStart, keepAliveSeconds);
//
// inform the app that the app has successfully connected
broadcastServiceStatus("Connected");
// we are connected
connectionStatus = MQTTConnectionStatus.CONNECTED;
// we need to wake up the phone's CPU frequently enough so that the
// keep alive messages can be sent
// we schedule the first one of these now
scheduleNextPing();
return true;
} catch (MqttException e) {
// something went wrong!
connectionStatus = MQTTConnectionStatus.NOTCONNECTED_UNKNOWNREASON;
//
// inform the app that we failed to connect so that it can update
// the UI accordingly
broadcastServiceStatus("Unable to connect");
//
// inform the user (for times when the Activity UI isn't running)
// that we failed to connect
notifyUser("Unable to connect", "MQTT", "Unable to connect - will retry later");
// if something has failed, we wait for one keep-alive period before
// trying again
// in a real implementation, you would probably want to keep count
// of how many times you attempt this, and stop trying after a
// certain number, or length of time - rather than keep trying
// forever.
// a failure is often an intermittent network issue, however, so
// some limited retry is a good idea
scheduleNextPing();
return false;
}
}