CODEWITHSUNDEEP
dartflutter
SteAp
SteAp

Reputation: 11999

How to cancel a running Timer() when Widget disappears

In a StatefulWidget, I implemented a deactivate() method, which does some cleanup.

Actually, the StatefulWidget periodically polls a service and reloads itself with newly received data. Therefore, it uses a Timer(), which periodically calls the server polling callback.

The deactivate() gets called just fine. But at some deactivations of the widget, the asynchronous Timer() still fires a last event and calls the callback - while the widget is partly deactivated.

This is my deactivate():

  @protected
  @mustCallSuper
  void deactivate() {

    // allow callback of Timeer() to not execute 
    _timerCanceled = true;

    // Cancel the periodic Timer()
    _timer.cancel();

    // Should be called LAST or FIRST?
    super.deactivate();

  }

Q:General question: How to cancel some asynchronous Timer() and ensure, that it doesn't any longer calls the provided callback.

Or: How to write code that cancels a Timer() and execute code after a complete cancel operation, so that the callback of the Timer() definitely won't get called.

Upvotes: 4

Views: 7687

Answers (1)

matanlurey
matanlurey

Reputation: 8614

In the Flutter gallery application example, they use override dispose in their State class:

@override
void dispose() {
  _timeDilationTimer?.cancel();
  super.dispose();
}

I am not confident that is correct to create the Timer inside the StatefulWidget. You might want to refer to the gallery example (and other examples in the Flutter repository).

Upvotes: 10

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