Future doWhile(dynamic f())

Perform an async operation repeatedly until it returns false.

Runs f repeatedly, starting the next iteration only when the Future returned by f completes to true. Returns a Future that completes once f returns false.

The return values of all Futures are discarded. Any errors will cause the iteration to stop and will be piped through the returned Future.

The function f may return either a bool or a Future that completes to a bool. If it returns a non-Future, iteration continues immediately. Otherwise it waits for the returned Future to complete.

Source 

static Future doWhile(f()) {
  _Future doneSignal = new _Future();
  var nextIteration;
  // Bind this callback explicitly so that each iteration isn't bound in the
  // context of all the previous iterations' callbacks.
  nextIteration = Zone.current.bindUnaryCallback((bool keepGoing) {
    if (keepGoing) {
      new Future.sync(f).then(nextIteration,
                              onError: doneSignal._completeError);
    } else {
      doneSignal._complete(null);
    }
  }, runGuarded: true);
  nextIteration(true);
  return doneSignal;
}