【Android】使用ConnectivityManager與NetworkInfo實現判斷當前網絡環境是否可用

public class

ConnectivityManager

extends Object

java.lang.Object
↳	android.net.ConnectivityManager

 這個類用來查詢當前網絡狀態，通知網絡狀態變化。

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. 監視網絡連接（WIFI，GPRS，UMTS等）
6. 當網絡變化時發出broadcast.
7. 當目前的網絡丟失的時候嘗試轉移到另一個網絡
8. 提供API來允許AP查詢當前可用網絡的精確度

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).

描述目前網絡的狀態（）

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.

一個用上面兩個類實現的查詢當前網絡狀態是否可用的工具類：

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;
}

上面這個類實現了單獨查詢WiFi與Mobile的移動網絡是否可用，可以看到就是使用了ConnectivityManager與NetworkInfo提供的接口實現的功能！

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則實現了所有網絡是否可用的判斷，程序不關心當前使用的是何種網絡，只需關係是否連接上互聯網既可，第一個工具類在某些時候會需要使用到，比如只在WiFi情況下才進行下載的操作，等等。

謝謝！