Question

Anyone have example Rx code that shows how to execute an action due to a delayed event that is cancelled by another event? Such as, displaying a tooltip when hovering over a button for a certain period of time?

The action is “display tooltip”

The duration is the “certain period of time”

And the cancellation event would be “mouse out” if the mouse stops hovering over the button.

Thanks!

Answer 1

Always start by breaking down the problem into what you have and what you want, turn that into a function signature, and see if that reveals an implementation.

execute an action due to a delayed event that is cancelled by another event

so you have a trigger source, a delay duration, and a cancellation source

The desired behavior you describe is:

• For each source trigger
• Delay for a specified time
• If no cancel happens during that time, yield the original value

Now that we have the spec, we can make a signature and consider an implementation

??? DelayOrCancel<???>(this IObservable<T> source, 
                       TimeSpan delay, 
                       IObservable<TCancel> cancel);

Depending on the nature of the cancellation source, you could need to pass Func<T, IObservable<TCancel>>, but it sounds like this will work in your case.

The first two lines of the spec suggest SelectMany (each item in the source makes another observable that will be combined back to a single observable). To get the cancellation, we just need to wait for the delay or until a cancellation, which we can do with TakeUntil. Since the final items will be the source items, the return type will be the same as the source.

IObservable<T> DelayOrCancel<T, TCancel>(this IObservable<T> source, 
                                         TimeSpan delay, 
                                         IObservable<TCancel> cancel)
{
    //argument checking skipped
    return from s in source
           from i in Observable.Timer(delay).TakeUntil(cancel)
           select s;
}