先来看一下关于ConnectivityManager类的介绍。
/**
* 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
* {@link android.content.Context#getSystemService(String) Context.getSystemService(Context.CONNECTIVITY_SERVICE)}.
* <p>
* The primary responsibilities of this class are to:
* <ol>
* <li>Monitor network connections (Wi-Fi, GPRS, UMTS, etc.)</li>
* <li>Send broadcast intents when network connectivity changes</li>
* <li>Attempt to "fail over" to another network when connectivity to a network
* is lost</li>
* <li>Provide an API that allows applications to query the coarse-grained or fine-grained
* state of the available networks</li>
* </ol>
*/从上面的介绍中总结出该类的作用：
1.追踪网络的连接状态：WI-Fi,GPRS,UMTS,etc；
2.当网络状态发生改变时，发送广播sendBroadcast消息；
3.失效转移file over:当A网络断掉时，系统自动切换，B网络及时补上提供服务，用户不会察觉网络的改变；
4.提供查询的API:（我们一般使用两种：）连没连网络和连的是什么类型的网络（getNetworkInfo(network_type)）。
我们在需要监控网络状态时要注册广播接收器，BroadcastReceiver Action是：
public static final String CONNECTIVITY_ACTION = "android.net.conn.CONNECTIVITY_CHANGE";
看下注释
/**
* A change in network connectivity has occurred. A connection has either
* been established or lost. The NetworkInfo for the affected network is
* sent as an extra; it should be consulted to see what kind of
* connectivity event occurred.
* <p/>
* If this is a connection that was the result of failing over from a
* disconnected network, then the FAILOVER_CONNECTION boolean extra is
* set to true.
* <p/>
* For a loss of connectivity, if the connectivity manager is attempting
* to connect (or has already connected) to another network, the
* NetworkInfo for the new network is also passed as an extra. This lets
* any receivers of the broadcast know that they should not necessarily
* tell the user that no data traffic will be possible. Instead, the
* receiver should expect another broadcast soon, indicating either that
* the failover attempt succeeded (and so there is still overall data
* connectivity), or that the failover attempt failed, meaning that all
* connectivity has been lost.
* <p/>
* For a disconnect event, the boolean extra EXTRA_NO_CONNECTIVITY
* is set to {@code true} if there are no connected networks at all.
*/从上面我们可以得到系统网络状态广播的情况：
1.网络的连接与断开
2.失效转移file over,其对应的标志FAILOVER_CONNECTION=true}
当无网络时，EXTRA_NO_CONNECTIVITY=true。
我们在查询网络状态时经常要区分出网络的类型：
public static final int TYPE_NONE = -1;
public static final int TYPE_MOBILE = 0; //基本通话用的网络，譬如3G，GPRS
public static final int TYPE_WIFI = 1;
public static final int TYPE_MOBILE_MMS = 2; //彩信网络
public static final int TYPE_MOBILE_SUPL = 3; //是一种基于标准、允许移动电话用户与定位服务器通信的协议
public static final int TYPE_MOBILE_DUN = 4; //网络桥接，很老的一个网络
public static final int TYPE_MOBILE_HIPRI = 5; //高优先级的移动数据连接。相同的为{TYPE_MOBILE}，但路由的设置是不同的。只有请求的进程将有机会获得移动的DNS服务器。
public static final int TYPE_WIMAX = 6; //全球微波互联接入
public static final int TYPE_BLUETOOTH = 7; //蓝牙
public static final int TYPE_DUMMY = 8; //虚拟连接
public static final int TYPE_ETHERNET = 9; //以太网
public static final int TYPE_MOBILE_FOTA = 10;
public static final int TYPE_MOBILE_IMS = 11;
public static final int TYPE_MOBILE_CBS = 12;
public static final int TYPE_WIFI_P2P = 13; //通过wifi直连wifi
public static final int TYPE_MOBILE_IA = 14;TYPE_MOBILE_MMS,TYPE_MOBILE_SUPL,TYPE_MOBILE_DUN,TYPE_MOBILE_HIPRI,TYPE_MOBILE_FOTA,TYPE_MOBILE_IMS,TYPE_MOBILE_CBS,TYPE_MOBILE_A是属于MOBILE类型的。
TYPE_WIFI,case TYPE_WIFI_P2P是属于WIFI类型的。
我们在使用getNetworkInfo(networkType)来获得指定网络类型的状态信息。
public NetworkInfo getNetworkInfo(int networkType) {
try {
return mService.getNetworkInfo(networkType);
} catch (RemoteException e) {
return null;
}
}
返回值类型NetworkInfo中可以通过getType()获得的网络类型，可以通过getState()获得网络状态，状态值有下面几个：CONNECTING, CONNECTED, SUSPENDED,
DISCONNECTING, DISCONNECTED, UNKNOWN。
