问题
OS: Android
Given: User has stated that they wish to remain connected to app's server to receive updates, etc.
Goal: To ensure that users are connected to app's server even when app is in background state.
Question: One problem has been occasional disconnects from the network. If a user loses data network connectivity (loss of 2G, 3G, WiFi) and then later regains connectivity, our app is left without a connection. I am currently trying to make use of PhoneStateListener's in order to detect various network changes and thereby restart connectivity with the server when appropriate. On my Nexus One (2.1), I find that onSignalStrengthsChanged and onDataConnectionStateChanged aren't called except when the listeners are originally registered, but not afterwards. The listeners are registered inside of a Service so they are continuously listening as long as the Service is alive (which we can assume to be 'forever' for purposes of this question). Has anyone else had any issues with listening to the state of the Data Connection?
onServiceStateChanged seems to be the most reliable so far, but I wanted to know if people have had success with the other listeners as well.
回答1:
I guess you'll have to send keepalive messages at regular intervals to check whether the connection is still there. If not, reestablish it. There is a smorgasbord of reasons why your connection might drop, and you won't be able to check all of those client side.
Might consider using google's cloud service for what you're doing though, since they already keep an connection open for that. That way your user's phones won't have the overhead of keeping yet another connection around (which can be quite expensive)
回答2:
Since StackOverflow doesn't allow me to close the question otherwise, I will provide the answer to why my PhoneStateListeners were not working:
I discovered that my problem was simply that I wasn't registering my listeners in a bitwise manner, but rather successively (i.e.telephonyManager.listen(listener, PhoneStateListener.LISTEN_CALL_STATE);
telephonyManager.listen(listener, PhoneStateListener.LISTEN_DATA_CONNECTION_STATE);
.
.
.
instead of (the correct):telephonyManager.listen(listener, PhoneStateListener.LISTEN_CALL_STATE | PhoneStateListener.LISTEN_DATA_CONNECTION_STATE..............);)
I will close this question and perhaps later open a different question asking for design suggestion on maintaining 'always alive' connections to a server on Android. Thanks.
回答3:
As far as i know listeners could not be called when app is in background. You should try use services not activity.
And also remember to retrieve TelephonyManager in proper way
TelephonyManager mTelephonyMgr = (TelephonyManager)getActivity().getSystemService(Context.TELEPHONY_SERVICE);
回答4:
I would think you would use the ConnectivityManager for this.
Class that answers queries about the state of network connectivity. It also notifies applications when network connectivity changes. Get an instance of this class by calling Context.getSystemService(Context.CONNECTIVITY_SERVICE).
http://developer.android.com/reference/android/net/ConnectivityManager.html
per the docs, it monitors network connectivity and sends broadcast intents on change to applications.
来源：https://stackoverflow.com/questions/5089668/detecting-network-connectivity-on-android