WPF绑定定期更新

Question

I've got a complex back-end process that runs for a long period of time. All the vital stats are exposed as properties with INotifyPropertyChanged events raised when they're set.

I wanted to add an "Elapsed time" which is proving far more challenging than anticipated.

I exposed a ProcessStartedAt DateTime and threw together a converter to subtract the bound time from DateTime.Now . This works perfectly (once). After that, since the property isn't changing, the binding is never updated and the converter isn't called again.

I don't want the back-end to have a timer dedicated to updating an "Elapsed time" property. It violates the separation of concerns principle. I'd be happier with a timer in the UI but am unsure how to force a binding to refresh without updating the property value.

Even better, is there a way I can tell the binding to refresh at regular intervals?

<TextBlock Text="{Binding Path=ProcessStartedAt,
                          Converter={StaticResource ElapsedTime}}"/>

Answer 1

I would throw the timer inside the ValueConverter class and raise an event to call the Convert method each time the interval is hit.

This keeps that ValueConverter focused on its responsibility.

Answer 2

No need for converter, just notify delaying on the getter:

public string RemainingTime
{
    get {
           Task.Delay(1000).
           ContinueWith(w => OnPropertyChanged(() => RemainingTime));
           return (CurrentServerTime - SelectedDeliveryTime).ToString("mm\\:ss");
        }
}

The binding will be recalled because of the OnPropertyChange

Answer 3

'I've got a complex back-end process that runs for a long period of time.' and 'I don't want the back-end to have a timer dedicated to updating an "Elapsed time" property.' seems a little counterproductive.

Trying to not update the view with your view-model seems to violate some MVC principles. Suppose you find a way to do so, the following engineer/developer might not.

Maybe you should find a way to timely change your view-model class timely instead of trying to 'block' updates in a timely manner. In that way you wouldn't have to concern about how things are updated. Instead, you would 'apply' changes to your view-model in a way that are easy to understand, change in the future and also be able to update technology when updates do framework are applied.

EDIT

I guess the only way is to set a DispatcherTimer, subscribe to it and call the OnPropertyChanged. Not related to your question, but you can also put a Delay to your Binding if needed.