then<R> method

CancelableOperation<R> then<R>(
  1. FutureOr<R> onValue(
    1. T
    ), {
  2. FutureOr<R> onError(
    1. Object,
    2. StackTrace
    )?,
  3. FutureOr<R> onCancel()?,
  4. bool propagateCancel = true,
})

Creates a new cancelable operation to be completed when this operation completes normally or as an error, or is cancelled.

If this operation completes normally the value is passed to onValue and the returned operation is completed with the result.

If this operation completes as an error, and no onError callback is provided, the returned operation is completed with the same error and stack trace. If this operation completes as an error, and an onError callback is provided, the returned operation is completed with the result.

If this operation is canceled, and no onCancel callback is provided, the returned operation is canceled. If this operation is canceled, and an onCancel callback is provided, the returned operation is completed with the result.

At most one of onValue, onError, or onCancel will be called. If any of onValue, onError, or onCancel throw a synchronous error, or return a Future that completes as an error, the error will be forwarded through the returned operation.

If the returned operation is canceled before this operation completes or is canceled, the onValue, onError, and onCancel callbacks will not be invoked. If propagateCancel is true (the default) then this operation is canceled as well. Pass false if there are multiple listeners on this operation and canceling the onValue, onError, and onCancel callbacks should not cancel the other listeners.

Implementation

CancelableOperation<R> then<R>(FutureOr<R> Function(T) onValue,
        {FutureOr<R> Function(Object, StackTrace)? onError,
        FutureOr<R> Function()? onCancel,
        bool propagateCancel = true}) =>
    thenOperation<R>((value, completer) {
      completer.complete(onValue(value));
    },
        onError: onError == null
            ? null
            : (error, stackTrace, completer) {
                completer.complete(onError(error, stackTrace));
              },
        onCancel: onCancel == null
            ? null
            : (completer) {
                completer.complete(onCancel());
              },
        propagateCancel: propagateCancel);