A way to produce Future objects and to complete them later with a value or error.

Most of the time, the simplest way to create a future is to just use one of the Future constructors to capture the result of a single asynchronous computation:

new Future(() { doSomething(); return result; });

or, if the future represents the result of a sequence of asynchronous computations, they can be chained using Future.then or similar functions on Future:

Future doStuff(){
  return someAsyncOperation().then((result) {
    return someOtherAsyncOperation(result);
  });
}

If you do need to create a Future from scratch — for example, when you're converting a callback-based API into a Future-based one — you can use a Completer as follows:

class AsyncOperation {
  Completer _completer = new Completer();

  Future<T> doOperation() {
    _startOperation();
    return _completer.future; // Send future object back to client.
  }

  // Something calls this when the value is ready.
  void _finishOperation(T result) {
    _completer.complete(result);
  }

  // If something goes wrong, call this.
  void _errorHappened(error) {
    _completer.completeError(error);
  }
}

Constructors

Completer()

Creates a new completer.

factory
Completer.sync()

Completes the future synchronously.

factory

Properties

future Future<T>

The future that will contain the result provided to this completer.

read-only
isCompleted bool

Whether the future has been completed.

read-only
hashCode int

The hash code for this object.

read-only, inherited
runtimeType Type

A representation of the runtime type of the object.

read-only, inherited

Operators

operator ==(other) bool

The equality operator.

inherited

Methods

complete([value ]) → void

Completes future with the supplied values.

completeError(Object error, [ StackTrace stackTrace ]) → void

Complete future with an error.

noSuchMethod(Invocation invocation) → dynamic

Invoked when a non-existent method or property is accessed.

inherited
toString() String

Returns a string representation of this object.

inherited