method

doWhile

Source

/**
 * 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 [Future]s 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.
 */
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;
}