【Android】使用ConnectivityManager与NetworkInfo实现判断当前网络环境是否可用

public class

ConnectivityManager

extends  Object

java.lang.Object
↳	android.net.ConnectivityManager

 这个类用来查询当前网络状态，通知网络状态变化。

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 callingContext.getSystemService(Context.CONNECTIVITY_SERVICE).

The primary responsibilities of this class are to:

1. Monitor network connections (Wi-Fi, GPRS, UMTS, etc.) 
2. Send broadcast intents when network connectivity changes
3. Attempt to "fail over" to another network when connectivity to a network is lost
4. Provide an API that allows applications to query the coarse-grained or fine-grained state of the available networks.                                                                           
5. 监视网络连接（WIFI，GPRS，UMTS等）
6. 当网络变化时发出broadcast.
7. 当目前的网络丢失的时候尝试转移到另一个网络
8. 提供API来允许AP查询当前可用网络的精确度

NetworkInfo	getActiveNetworkInfo()
NetworkInfo[]	getAllNetworkInfo()
boolean	getBackgroundDataSetting() This method is deprecated. As of ICE_CREAM_SANDWICH, availability of background data depends on several combined factors, and this method will always returntrue. Instead, when background data is unavailable, getActiveNetworkInfo() will now appear disconnected.
NetworkInfo	getNetworkInfo(int networkType)
int	getNetworkPreference()
static boolean	isNetworkTypeValid(int networkType)
boolean	requestRouteToHost(int networkType, int hostAddress) Ensure that a network route exists to deliver traffic to the specified host via the specified network interface.
void	setNetworkPreference(int preference)
int	startUsingNetworkFeature(int networkType, String feature) Tells the underlying networking system that the caller wants to begin using the named feature.
int	stopUsingNetworkFeature(int networkType, String feature) Tells the underlying networking system that the caller is finished using the named feature.

public class

NetworkInfo

extends  Object
implements  Parcelable

java.lang.Object
↳	android.net.NetworkInfo

Describes the status of a network interface of a given type (currently either Mobile or Wifi).

描述目前网络的状态（）

Detailed state	Coarse-grained state
IDLE	DISCONNECTED
SCANNING	CONNECTING
CONNECTING	CONNECTING
AUTHENTICATING	CONNECTING
CONNECTED
DISCONNECTING	DISCONNECTING
DISCONNECTED	DISCONNECTED
UNAVAILABLE	DISCONNECTED
FAILED	DISCONNECTED

Public Methods
NetworkInfo.DetailedState	getDetailedState() Reports the current fine-grained state of the network.
String	getExtraInfo() Report the extra information about the network state, if any was provided by the lower networking layers., if one is available.
String	getReason() Report the reason an attempt to establish connectivity failed, if one is available.
NetworkInfo.State	getState() Reports the current coarse-grained state of the network.
int	getSubtype() Return a network-type-specific integer describing the subtype of the network.
String	getSubtypeName() Return a human-readable name describing the subtype of the network.
int	getType() Reports the type of network (currently mobile or Wi-Fi) to which the info in this object pertains.
String	getTypeName() Return a human-readable name describe the type of the network, for example "WIFI" or "MOBILE".
boolean	isAvailable() Indicates whether network connectivity is possible.
boolean	isConnected() Indicates whether network connectivity exists and it is possible to establish connections and pass data.
boolean	isConnectedOrConnecting() Indicates whether network connectivity exists or is in the process of being established.
boolean	isFailover() Indicates whether the current attempt to connect to the network resulted from the ConnectivityManager trying to fail over to this network following a disconnect from another network.
boolean	isRoaming() Indicates whether the device is currently roaming on this network.
String	toString() Returns a string containing a concise, human-readable description of this object.

一个用上面两个类实现的查询当前网络状态是否可用的工具类：

	public static boolean isNetworkAvailable(Context context)
	{
		ConnectivityManager mConnMgr = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
		NetworkInfo mWifi = mConnMgr.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
		NetworkInfo mMobile = mConnMgr.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);
		boolean flag = false;
		if((mWifi != null)	&& ((mWifi.isAvailable()) || (mMobile.isAvailable())))
		{
			if((mWifi.isConnected()) || (mMobile.isConnected()))
			{
				flag = true;
			}
		}
		return flag;
	}

上面这个类实现了单独查询WiFi与Mobile的移动网络是否可用，可以看到就是使用了ConnectivityManager与NetworkInfo提供的接口实现的功能！

public static boolean isConnectionAvailable(Context cotext) 
	{
    	boolean isConnectionFail = true;
    	ConnectivityManager connectivityManager = (ConnectivityManager)cotext.getSystemService(Context.CONNECTIVITY_SERVICE);
		if (connectivityManager != null) 
		{
			NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo();					
			if (activeNetworkInfo == null || !activeNetworkInfo.isConnected()) 
			{				
				isConnectionFail = true;
			} 
			else 
			{
				isConnectionFail = false;
			}
		} 
		else 
		{
			Log.e(TAG, "Can't get connectivitManager");
		}
		return isConnectionFail;
	}

isConnectionAvailable则实现了所有网络是否可用的判断，程序不关心当前使用的是何种网络，只需关系是否连接上互联网既可，第一个工具类在某些时候会需要使用到，比如只在WiFi情况下才进行下载的操作，等等。

谢谢！