Flutter get continuous stream of data from MethodChannels native api - flutter

Question

I am using Method Channel to integrate android s3 upload .
Upload is working alright. The android sdk provides two methods onStateChanged and OnProgressChanged to tell state of upload and how many bytes have been uploaded. The problem is I can't seem to get this data returned from the method channel to main flutter file.
public class MainActivity extends FlutterActivity {
private static final String CHANNEL = "s3integration";
AmazonS3 s3Client;
String bucket = "instituteimages";
#Override
public void configureFlutterEngine(#NonNull FlutterEngine flutterEngine) {
GeneratedPluginRegistrant.registerWith(flutterEngine);
s3credentialsProvider();
new MethodChannel(flutterEngine.getDartExecutor().getBinaryMessenger(),CHANNEL).setMethodCallHandler((call, result)->{
if(call.method.equals("uploadFiles")){
String filePath = call.argument("path");
String fileName = call.argument("fileName");
File uploadFile = new File(filePath);
TransferUtility transferUtility= new TransferUtility(s3Client,getApplicationContext());
TransferObserver transferObserver = transferUtility.upload(
bucket, /* The bucket to upload to */
fileName,/* The key for the uploaded object */
uploadFile /* The file where the data to upload exists */
);
transferObserverListener(transferObserver);
TransferState finalState = transferObserver.getState();
HashMap<String,String> statusJson= new HashMap<>();
statusJson.put("status","Success");
statusJson.put("url",String.format("https://awsurl/%s",fileName));
result.success(statusJson);
}
});
public void transferObserverListener(TransferObserver transferObserver) {
transferObserver.setTransferListener(new TransferListener() {
#Override
public void onStateChanged(int id, TransferState state) {
Toast.makeText(getApplicationContext(), "State Change"
+ state, Toast.LENGTH_SHORT).show();
}
#Override
public void onProgressChanged(int id, long bytesCurrent, long bytesTotal) {
int percentage = (int) (bytesCurrent / bytesTotal * 100);
Toast.makeText(getApplicationContext(), "Uploading ..."
+ percentage, Toast.LENGTH_SHORT).show();
}
#Override
public void onError(int id, Exception ex) {
Log.e("error", "error");
}
});
}
As you can see I can get the required states and values from OnStateChanged and OnProgressChanged but I can't return them in result.success, if I do that only the initial values of these variables are returned not the continues stream of them.
Here is flutter code I am calling this upload code from:
class UploadVideo extends StatefulWidget {
TeacherUser user = TeacherUser();
UploadVideo(this.user);
#override
State<StatefulWidget> createState() {
return _UploadVideo(this.user);
}
}
class _UploadVideo extends State<UploadVideo> {
TeacherUser user = TeacherUser();
_UploadVideo(this.user);
static const aws_platform = const MethodChannel('s3integration');
String baseBucketUrl = 'https://s3baseurl/';
String title = titleTextController.text;
String path = imagePath.path;
String fileName = imagePath.path.toString().split('/').last.toString();
try{
var res = await aws_platform.invokeMethod('uploadFiles','path':path,'fileName':fileName});
if(res['status']=='Success'){
var response = postUploadVideo(
user.key, title, groupSub, groupChap, finalUrl, generalVideo);
print('total response ${response.toString()}');
Navigator.pop(context);
}
else{
Fluttertoast.showToast(msg: 'Upload failed. Please try again.');
Navigator.pop(context);
}
Navigator.pop(context);
}
on PlatformException catch(e){
print('platform error ${e.toString()}');
}
How can I receive stream of data from MethodChannel so that I can show some kind of progress bar in my flutter code.