How can I include native code in Flutter to display a KML Layer on Google Map? - google-maps

Question

I've been looking into running native code in my Flutter app to display a KML Layer on my Google Map and while I do have the app running native code (at least on Android), I am having difficulty with getting the KML stuff to work.
I have created a MethodChannel in my Flutter class to run the native code and this works fine. Please see below.
// Run java code for KML Campus Map Overlay
Future<void> _showCampusMap() async {
const platform = MethodChannel('uk.ac.manchestermaps/kmlLayer');
try {
final campusMapOverlay =
await platform.invokeMethod('retrieveFileFromUrl');
print(campusMapOverlay);
} on PlatformException catch (error) {
print(error);
}
}
I am taking some code that I used on the Android only pre-alpha version of the app, so I know it works, but I have 4 errors.
In my MainActivity java file,I have these package.
import android.os.Bundle;
import io.flutter.app.FlutterActivity;
import io.flutter.plugins.GeneratedPluginRegistrant;
import io.flutter.plugin.common.MethodCall;
import io.flutter.plugin.common.MethodChannel;
import io.flutter.plugin.common.MethodChannel.Result;
import io.flutter.plugin.common.MethodChannel.MethodCallHandler;
import org.xmlpull.v1.XmlPullParserException;
import android.os.AsyncTask;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
and the MainActivity class consists of this.
public class MainActivity extends FlutterActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
GeneratedPluginRegistrant.registerWith(this);
new MethodChannel(getFlutterView(), "**<MY CHANNEL>**").setMethodCallHandler(new MethodCallHandler() {
#Override
public void onMethodCall(MethodCall call, MethodChannel.Result result) {
if (call.method.equals("retrieveFileFromUrl")) {
retrieveFileFromUrl();
result.success("KMLLayer Retrieved");
}
}
});
}
private void retrieveFileFromUrl() {
new DownloadKmlFile("**<REMOTE KML FILE>**")
.execute();
}
private class DownloadKmlFile extends AsyncTask<String, Void, byte[]> {
private final String mUrl;
public DownloadKmlFile(String url) {
mUrl = url;
}
protected byte[] doInBackground(String... params) {
try {
InputStream is = new URL(mUrl).openStream();
// Log.d(TAG, "doInBackground: " + mUrl.toString());
ByteArrayOutputStream buffer = new ByteArrayOutputStream();
int nRead;
byte[] data = new byte[16384];
while ((nRead = is.read(data, 0, data.length)) != -1) {
buffer.write(data, 0, nRead);
}
buffer.flush();
return buffer.toByteArray();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
protected void onPostExecute(byte[] byteArr) {
try {
KmlLayer kmlLayer = new KmlLayer(mMap, new ByteArrayInputStream(byteArr), getApplicationContext());
kmlLayer.addLayerToMap();
// moveCameraToKml(kmlLayer);
} catch (XmlPullParserException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
Here are my errors
Running Gradle task 'assembleDebug'...
.....\MainActivity.java:73: error: cannot find symbol
KmlLayer kmlLayer = new KmlLayer(mMap, new ByteArrayInputStream(byteArr), getApplicationContext());
^
symbol: class KmlLayer
location: class MainActivity.DownloadKmlFile
.....\MainActivity.java:73: error: cannot find symbol
KmlLayer kmlLayer = new KmlLayer(mMap, new ByteArrayInputStream(byteArr), getApplicationContext());
^
symbol: class KmlLayer
location: class MainActivity.DownloadKmlFile
.....\MainActivity.java:73: error: cannot find symbol
KmlLayer kmlLayer = new KmlLayer(mMap, new ByteArrayInputStream(byteArr), getApplicationContext());
^
symbol: variable mMap
location: class MainActivity.DownloadKmlFile
3 errors
I have looked around, but can't find anything to help this this specific case as I don't think a lot of people are doing on it. I know KML support has been request for the google_maps_flutter package, but it seems to have gone quiet.
Any help with this would be very much appreciated, as it is pretty central to the app I am developing. Without this, the app is next to useless.
Thanks