Cancellable mixin

A mixin for making a class cancellable using a CancellationToken.

To implement this mixin on a custom cancellable:

• Call maybeAttach to attach to the token before starting async work. If false is returned, the token has already been cancelled and no async operations should be started.
• Override onCancel to handle cancellation.
• Call detach after all async operations complete.

It's good practice to make any token parameters nullable to make cancellation optional.

class MyCancellable with Cancellable {
  MyCancellable(this.cancellationToken) {
    // Call `maybeAttach()` to only attach if the cancellation token hasn't
    // already been cancelled
    if (maybeAttach(this.cancellationToken)) {
      // Start your async task here
    }
  }

  final CancellationToken cancellationToken;

  @override
  void onCancel(Exception cancelException) {
    super.onCancel(exception);
    // Clean up resources here, like closing an HttpClient, and complete
    // any futures or streams
  }

  void complete() {
    // If your async task completes before the token is cancelled,
    // detatch from the token
    detach();
  }
}

Mixin Applications

• CancellableCompleter
• MergedCancellationToken

Properties

cancellationStackTrace → StackTrace

The stack trace at the time this cancellable was created.

final

hashCode → int

The hash code for this object.

no setter, inherited

isCancelled → bool

Whether or not the operation has been cancelled.

no setter

runtimeType → Type

A representation of the runtime type of the object.

no setter, inherited

Methods

detach() → void

Detatches from the CancellationToken. This should be called after completing without cancellation.

maybeAttach(CancellationToken? token) → bool

Attaches to the CancellationToken only if it hasn't already been cancelled. If the token has already been cancelled, onCancel is called instead.

noSuchMethod(Invocation invocation) → dynamic

Invoked when a nonexistent method or property is accessed.

inherited

onCancel(Exception cancelException) → void

Called when the attached token is cancelled.

toString() → String

A string representation of this object.

inherited

Operators

operator ==(Object other) → bool

The equality operator.

inherited