dart:async

Completer abstract class

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()

factory

Creates a new completer.

Completer.sync()

factory

Completes the future synchronously.

Properties

future → Future<T>

read-only

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

isCompleted → bool

read-only

Whether the future has been completed.

hashCode → int

read-only, inherited

The hash code for this object.

runtimeType → Type

read-only, inherited

A representation of the runtime type of the object.

Operators

operator ==(other) → bool

inherited

The equality operator.

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

inherited

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

toString() → String

inherited

Returns a string representation of this object.