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();
        }
    }
}