Why is this double-click detection code unreliable?

问题

I'm trying to learn Rx through some simple challenges, first by detecting double-clicks by watching only MouseUp events. I came up with the following solution (this code is compilable by creating a WPF project and adding the Reactive Extensions NuGet package):

using System;
using System.Reactive.Linq;
using System.Windows.Input;

namespace WpfApplication1 {
    public partial class MainWindow {
        public MainWindow() {
            InitializeComponent();
            var clickEvents = Observable
                .FromEventPattern<MouseButtonEventArgs>(this, "MouseLeftButtonUp");

            var intraClickInterval = TimeSpan.FromMilliseconds(500);
            var interClickInterval = TimeSpan.FromMilliseconds(1000);

            var doubleClicks = clickEvents
                .TimeInterval()
                .SkipWhile(t => t.Interval < interClickInterval)
                .FirstAsync(t => t.Interval < intraClickInterval)
                .Repeat();

            var doubleClickReady = doubleClicks
                .Delay(interClickInterval)
                .Subscribe(e => Console.WriteLine("Now accepting double click!"));

            doubleClicks.Subscribe(e => Console.WriteLine(e.Interval));
        }
    }
}

Most solutions I've seen don't deal with multiple clicks, so the idea is to always wait for a certain interval (interClickInterval) between each double-click, and then a double-click is the next mouse up event that has an interval smaller than the intraClickInterval. I've also added a message that gets printed after the interClickInterval elapses following each double-click so that I know when double-clicks are supposed to register.

This seems to work well in general, but it seems that sometimes they do not register even though I see the "Now accepting double-click!" message. This seems to happen particularly if I click just before the message appears. What could be causing this?

EDIT: I think the double-click detection is actually correct, it's the message that isn't. Basically, it ignores any subsequent click after a double-click. I'd need to do something like

for each double click event
wait for the interClickInterval
if no click was registered since, display "Now accepting double click!"

But I'm not sure how to achieve that...

回答1:

So as I suspected, the detection code is correct, it's the message that was timed incorrectly. It didn't take into account any subsequent clicks after a double-click; it just always printed its message 1000ms after each double-click. Here's a version of the ready message that correctly waits for 1000ms to have elapsed since the last click after each double-click:

        var doubleClickReady = doubleClicks
            .SelectMany(clickEvents
                .Buffer(interClickInterval)
                .FirstAsync(b => b.Count == 0));

        doubleClickReady
            .Subscribe(e => Console.WriteLine("Now accepting double click!"));

来源：https://stackoverflow.com/questions/23715940/why-is-this-double-click-detection-code-unreliable

标签

wpf

system.reactive