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);
}
}
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.
Constructors
- Completer()
-
Creates a new completer.…
- Completer.sync()
-
Completes the future synchronously.…
Methods
-
complete(
[value]) → void -
completeError(
Object error, [StackTrace stackTrace]) → void