EventAggregator postpone a message for later use

Question

I really like the functionality the EventAggregator from Prism offers me to loosely couple my classes. But now I have a problem which is not covered by the EventAggregator.

So let us assume I publish the message "Test" and at the moment there is no subscriber of this message. Is it possible to postpone it until a subscriber exists?

Regards

Answer 1

This is easy enough to implement. Define a second message that will be published later and a class that contains the message and a timer:

public class OriginalMessage : CompositePresentationEvent<OriginalArgs> { }
public class MyDelayedMessage : CompositePresentationEvent<MyEventArgs> { }

public class DelayedMessage {
    EventAggregator _bus;
    OriginalMessage _msg;
    DispatcherTimer _timer;
    OriginalArgs _args;

    public DelayedMessage(
        EventAggregator bus,
        OriginalMessage sourceMessage,
        OriginalArgs args,
        TimeSpan delay
    ) {
        _bus = bus;
        _args = args;
        _msg = sourceMessage;
        _timer = new DispatcherTimer();
        _timer.Interval = delay;
        _timer.Tick += OnTimerTick;
    }

    void OnTimerTick(object sender, EventArgs args) {

        _bus.GetEvent<MyDelayedMessage>().Publish(_args);
    }
}

You'll need a context to place this object to keep it around. You can drop it onto the host IU container as a private field.