EventChannel class

Creates channel that will subscribe to an event source using the subscribe method. Incoming events from the event source will be queued in the channel until interested takers are registered.

To notify the channel that the event source has terminated, you can notify the provided subscriber with an End

Example

In the following example we create an event channel that will subscribe to a Timer.periodic

 EventChannel countdown(int secs) {
   return EventChannel(subscribe: (emitter) {
     var v = secs;
     var timer = Timer.periodic(Duration(seconds: 1), (timer) {
       v--;
       if (v > 0) {
         emitter(v);
       } else {
         emitter(End);
       } // this causes the channel to close
     });

     // The subscriber must return an unsubscribe function
     return () => timer.cancel();
   });
 }

 saga() sync* {
   var value = 10;
   var channel = Result<EventChannel>();

   yield Call(countdown, args: [value], result: channel);

   yield Try(() sync* {
     while (true) {
       // Take(pattern:End) will cause the saga to terminate
       // by jumping to the finally block
       var seconds = Result();
       yield Take(channel: channel.value, result: seconds);
       print('countdown: ${seconds.value}');
     }
   }, Finally: () sync* {
     print('countdown terminated');
   });
 }

Output

 countdown: 9
 countdown: 8
 countdown: 7
 countdown: 6
 countdown: 5
 countdown: 4
 countdown: 3
 countdown: 2
 countdown: 1
 countdown terminated

Constructors

EventChannel(Subscribe subscribe, {Buffer? buffer})

Creates an instance of an EventChannel

Properties

hashCode → int

The hash code for this object.

no setter, inherited

onClose ↔ Callback?

Invoked before closing the channel. Then all the awating takers will be invoked with End

getter/setter pair, inherited

runtimeType → Type

A representation of the runtime type of the object.

no setter, inherited

Methods

close() → void

Closes the channel which means no more puts will be allowed. All pending takers will be invoked with End.

inherited

flush(TakeCallback<List> callback) → void

Used to extract all buffered messages from the channel. The flush is resolved using the following rules

inherited

noSuchMethod(Invocation invocation) → dynamic

Invoked when a nonexistent method or property is accessed.

inherited

put(dynamic message) → void

Used to put message on the buffer. The put will be handled using the following rules

inherited

take(TakeCallback callback, [PatternMatcher? matcher]) → void

Used to register a taker. The take is resolved using the following rules

inherited

toString() → String

A string representation of this object.

inherited

Operators

operator ==(Object other) → bool

The equality operator.

inherited