Cancel class

If tasks provided then creates an Effect description that instructs the middleware to cancel a previously forked tasks, otherwise creates an Effect description that instructs the middleware to cancel a task in which it has been yielded (self-cancellation). Self-cancellation allows to reuse destructor-like logic inside a Finally blocks.

tasks is a list of tasks that each member is returned by a previous Fork.

Notes

To cancel a running task, the middleware will stop underlying Generator object. This will cancel the current Effect in the task and jump to the finally block (if defined).

Inside the finally block, you can execute any cleanup logic or dispatch some action to keep the store in a consistent state (e.g. reset the state of a spinner to false when an ajax request is cancelled). You can check inside the finally block if a Saga was cancelled by issuing a yield Cancelled().

Cancellation propagates downward to child sagas. When cancelling a task, the middleware will also cancel the current Effect (where the task is currently blocked). If the current Effect is a call to another Saga, it will be also cancelled. When cancelling a Saga, all attached forks (sagas forked using yield Fork()) will be cancelled. This means that cancellation effectively affects the whole execution tree that belongs to the cancelled task.

Cancel is a non-blocking Effect. i.e. the Saga executing it will resume immediately after performing the cancellation.

For functions which return Future results, you can plug your own cancellation logic by using FutureWithCancel type.

The following example shows how to attach cancellation logic to a Future result:

 import 'package:redux_saga/redux_saga.dart';
 import 'Api.dart';

 //...

 myApi() {
   Future result = myXhr(...);

   var cancelCallback = () {
     myXhr.abort();
   };

   return FutureWithCancel(result, cancelCallback);
 }

 mySaga() sync* {
   var task = Result<Task>();
   yield Fork(myApi, result: task);

   // ... later
   // will call cancelCallback on the result of myApi
   yield Cancel([task.value]);
 }

The following example shows how to self-cancel task and check cancellation if task is cancelled at finally block.

 import 'package:redux_saga/redux_saga.dart';
 import 'Api.dart';

 //...

 deleteRecord({ payload }) sync* {
   yield Try(() sync* {
     var result = Result();
     yield Call(prompt, result: result);
     if (result.value == confirm) {
       yield Put(DeleteRecord('confirm', payload));
     }
     if (result.value == deny) {
       yield Cancel();
     }
   }, Catch: (e, s) {
     // handle failure
   }, Finally: () sync* {
     var cancelled = Result();
     yield Cancelled(result: cancelled);
     if (cancelled.value) {
       // shared cancellation logic
       yield Put(DeleteRecord('cancel', payload));
     }
   });
 }

Notes

Constructors

Properties

Methods

Operators

redux_saga library