1. FutureOr<bool>action()

Performs an operation repeatedly until it returnsfalse.

The operation,action, may be either synchronous or asynchronous.

The operation is called repeatedly as long as it returns either theboolvaluetrue or aFuture<bool> which completes with the valuetrue.

If a call toaction returnsfalse or aFuture that completes tofalse, iteration ends and the future returned bydoWhile is completedwith anull value.

If a call toaction throws or a future returned byaction completeswith an error, iteration ends and the future returned bydoWhilecompletes with the same error.

Calls toaction may happen at any time,including immediately after callingdoWhile.The only restriction is a new call toaction won't happen beforethe previous call has returned, and if it returned aFuture<bool>, notuntil that future has completed.

Example:

void main() async {  var value = 0;  await Future.doWhile(() async {    value++;    await Future.delayed(const Duration(seconds: 1));    if (value == 3) {      print('Finished with $value');      return false;    }    return true;  });}// Outputs: 'Finished with 3'

Implementation

static Future<void> doWhile(FutureOr<bool> action()) {  _Future<void> doneSignal = _Future<void>();  late void Function(bool) nextIteration;  // Bind this callback explicitly so that each iteration isn't bound in the  // context of all the previous iterations' callbacks.  // This avoids, e.g., deeply nested stack traces from the stack trace  // package.  nextIteration = Zone.current.bindUnaryCallbackGuarded((bool keepGoing) {    while (keepGoing) {      FutureOr<bool> result;      try {        result = action();      } catch (error, stackTrace) {        // Cannot use `_completeWithErrorCallback` because it completes        // the future synchronously.        doneSignal._asyncCompleteErrorObject(          _interceptCaughtError(error, stackTrace),        );        return;      }      if (result is Future<bool>) {        result.then(nextIteration, onError: doneSignal._completeError);        return;      }      keepGoing = result;    }    doneSignal._complete(null);  });  nextIteration(true);  return doneSignal;}