获取网络状态ConnectivityManager

//获取ConnectivityManager对象。

ConnectivityManager mana = getSystemService(Context.CONNECTIVITY_SERVICE);

//NetworkInfo对象用来描述网络信息。
//得到当前使用的网络
NetworkInfo activeNetworkInfo=mana.getActiveNetworkInfo();

//得到所有网络
NetworkInfo[] infos = mana.getAllNetworkInfo();

//获取首选网络
int networkType = mana.getNetworkPreference();
-----代码实现-------
manager = (ConnectivityManager) getSystemService(CONNECTIVITY_SERVICE);
NetworkInfo activeNetworkInfo = manager.getActiveNetworkInfo();
if(activeNetworkInfo==null||!activeNetworkInfo.isAvailable()){
    Toast.makeText(getApplicationContext(), "网络连接不可用", Toast.LENGTH_SHORT).show();
}else{//可能联网
    int networkType = activeNetworkInfo.getType();
    if(networkType == ConnectivityManager.TYPE_WIFI){
        Toast.makeText(getApplicationContext(), "当前成功连接WIFI"
              +activeNetworkInfo.isConnected(), Toast.LENGTH_SHORT).show();
    }else if(networkType==ConnectivityManager.TYPE_MOBILE){
        if(activeNetworkInfo.isRoaming()){
            Toast.makeText(getApplicationContext(), "当前成功连接漫游3G网络"
                      +activeNetworkInfo.isConnected(), Toast.LENGTH_SHORT).show();
        }else{
            Toast.makeText(getApplicationContext(), "当前成功连接非漫游3G网络"
                      +activeNetworkInfo.isConnected(), Toast.LENGTH_SHORT).show();
        }
    }
}

添加权限：

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