How to detect in Android if the device changed the type of wifi network to data and know the name of the network?

To detect changes in the network you must use a BroadcastReceiver

link

This is an example class to detect changes

public class NetworkStateReceiver extends BroadcastReceiver {
    public void onReceive(Context context, Intent intent) {  
     if(intent.getExtras() != null) {
        NetworkInfo ni = (NetworkInfo) intent.getExtras().get(ConnectivityManager.EXTRA_NETWORK_INFO);
        if(ni != null && ni.getState() == NetworkInfo.State.CONNECTED) {
            Log.i("Network", "Network connected : " + ni.getTypeName());
        } else if(intent.getBooleanExtra(ConnectivityManager.EXTRA_NO_CONNECTIVITY, Boolean.FALSE)) {
            Log.i("Network", "No existe conectividad!");
        }
   }
}

You have to register on your AndroidManifest.xml the BroadcastReceiver , with the intent-filter% % co:

<receiver android:name=".NetworkStateReceiver">
   <intent-filter>
      <action android:name="android.net.conn.CONNECTIVITY_CHANGE" />
   </intent-filter>
</receiver>

and add permission:

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