检测网络变化（wifi、2g、3g、4g）

1.注册广播"android.net.conn.CONNECTIVITY_CHANGE"和"android.net.wifi.STATE_CHANGE" 进行监听：

private class ConnectivityBroadcastReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(Context context, Intent intent) {
            try
            {
                String action = intent.getAction();
                Log.e("ConnectivityBroadcastReceiver", "action= "+action);
                if ((!action.equals(ConnectivityManager.CONNECTIVITY_ACTION)
                        && !action.equals(WifiManager.NETWORK_STATE_CHANGED_ACTION))
                        || !isListening_) {
                    return;
                }

                if(intent.getAction().equals(WifiManager.NETWORK_STATE_CHANGED_ACTION)) {
                    networkInfo_ = intent.getParcelableExtra(WifiManager.EXTRA_NETWORK_INFO);
                    if(networkInfo_.isConnected()) {
                        // WIFI is connected
                        state_ = NET_STATE_WIFI_CONNECTED;
                    }else{
                        state_ = NET_STATE_DISCONNECTED;
                    }
                } else if(intent.getAction().equals(ConnectivityManager.CONNECTIVITY_ACTION)) {
                    networkInfo_ = (NetworkInfo) intent.getParcelableExtra(ConnectivityManager.EXTRA_NETWORK_INFO);
                    String apn = networkInfo_.getExtraInfo();
                    Log.e("ConnectivityBroadcastReceiver", "apn= "+apn);
                    boolean noConnectivity = intent.getBooleanExtra(ConnectivityManager.EXTRA_NO_CONNECTIVITY, false);
                    if(networkInfo_.getType() == ConnectivityManager.TYPE_WIFI){
                        if ( networkInfo_.isConnected() ){
                            state_ = NET_STATE_WIFI_CONNECTED;
                        }else{
                            state_ = noConnectivity ? NET_STATE_DISCONNECTED : NET_STATE_WIFI_CONNECTED;
                        }
                    }else if(networkInfo_.getType() == ConnectivityManager.TYPE_MOBILE){
                        if (noConnectivity) {
                            state_ = NET_STATE_DISCONNECTED;
                        } else {
                            TelephonyManager telephonyManager = (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
                            int type = telephonyManager.getNetworkType();
                            Log.e("ConnectivityBroadcastReceiver", "type= "+type);
                            state_ = getNetworkClass(type);
                        }
                    }else {
                        if (noConnectivity) {
                            state_ = NET_STATE_DISCONNECTED;
                        } else {
                            state_ = NET_STATE_UNKNOWN;
                        }
                    }
                }
                NotifyEvent();
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }

        }
    };

2.判断TYPE_MOBILE下的网络类型：

private int getNetworkClass(int networkType) {
        switch (networkType) {
        case TelephonyManager.NETWORK_TYPE_GPRS:
        case TelephonyManager.NETWORK_TYPE_EDGE:
        case TelephonyManager.NETWORK_TYPE_CDMA:
        case TelephonyManager.NETWORK_TYPE_1xRTT:
        case TelephonyManager.NETWORK_TYPE_IDEN:
            return NET_STATE_2G_CONNECTED;
        case TelephonyManager.NETWORK_TYPE_UMTS:
        case TelephonyManager.NETWORK_TYPE_EVDO_0:
        case TelephonyManager.NETWORK_TYPE_EVDO_A:
        case TelephonyManager.NETWORK_TYPE_HSDPA:
        case TelephonyManager.NETWORK_TYPE_HSUPA:
        case TelephonyManager.NETWORK_TYPE_HSPA:
        case TelephonyManager.NETWORK_TYPE_EVDO_B:
        case TelephonyManager.NETWORK_TYPE_EHRPD:
        case TelephonyManager.NETWORK_TYPE_HSPAP:
            return NET_STATE_3G_CONNECTED;
        case TelephonyManager.NETWORK_TYPE_LTE:
            return NET_STATE_4G_CONNECTED;
        default:
            return NET_STATE_UNKNOWN;
        }
    }  

3.在AndroidManifest.xml中加上权限：

<uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>