How to perform Firebase Mutable Transaction Data with Flutter?

I have Swift code where I reduce or increase an int value for certain conditions. How can I replicate this with Flutter? Here is my Swift code..

//  2.  Decrease Value -= from NumberOnes
let decreaseRef = self.ref.child("NumberOnes/\(myfav1)/Value")
decreaseRef.runTransactionBlock { (currentData: FIRMutableData) -> FIRTransactionResult in
    if var data = currentData.value as? Int
    {
        var count = data
        count -= 1
        data = count
        currentData.value = data
        return FIRTransactionResult.success(withValue: currentData)
    }
    return FIRTransactionResult.success(withValue: currentData)
}

Also, if there's documentation/tutorials for this out there, please point me to it.

* UPDATE *

Here is my Flutter code...

fb.child('UserVideo/${userid}/Vid1').onValue.listen((Event event){
        if (event.snapshot != null){
          final vidID = event.snapshot.value["videoID"];
          fb.child('NumberOnes/${vidID}/Value').onValue.listen((Event newEvent){
            int vidValue = newEvent.snapshot.value;
            vidValue;
            print(vidValue);
            //vidValue = value;
            final value = vidValue--;

            fb.child('NumberOnes/${vidID}').update({
              'Value': value,
            });

          });

The problem with my Flutter code is that it doesn't stop decreasing. Is there a way around this?

Here is my solution. I worked it out from this answer here... Flutter Firebase update will not stop updating node?

Basically, I'm isolating the value once, manipulating it, then updating node with new info. I think this is much less efficient than the runTransactionBlock from the Firebase Swift SDK that brings back snapshot value as MutableData. If anyone finds a work around for this in the future please add answer.

if (vidRank == 1) {
  var event = await fb.child('UserVideo/${userid}/Vid1').once();
  if (event.snapshot != null){
    var vid1id = event.snapshot.value['videoID'].toString();
    var onesEvent = await fb.child('NumberOnes/${vid1id}').once();
    if (onesEvent.snapshot != null){
      var onesValue = (onesEvent.snapshot.value['Value'] as int);
      final vidValue = onesValue - 1;
      print("Inside  ${vidValue}");
      fb.child('NumberOnes/${vid1id}').update({
        'Value': vidValue
      });
    }
  }
}