How do GUI toolkits discriminate between a single and a double click?

As you can see in my previous question, I am currently struggling with single and double click events – I wanted to perform an action after a click and a completely different a开发者_开发百科ction after a double click. The problem is that the low-level events only tell me things like this was a mouse down or this was a mouse up and the total click count is == 2. It’s hard to discriminate between a single and a double click this way, since when the mouse comes up after a single click, I have to wait a while to make sure there’s not a second click coming.

Now I am wondering how different GUI toolkits handle this, as there’s no magical way around. You can’t have separate high-level single-click and double-click events without having the single-click event delayed or something, can you?

(It looks like the usual way to solve this is to have the single and double click actions related, like selection on the first click and app launch on the second. That way it does not matter that the single-click action is triggered along with the double-click one. Am I right?)

You always need some sort of timer to distinguish between single and double click. Think about it: you cannot predict whether a second click will happen once the first occurred, you just have to wait and see.

On iOS, you can have gesture recognizers. And if you only register a single tap recognizer it fires right away, but as soon you also register a double tap recognizer you notice that a single tap doesn't fire right away but only after a noticeable delay. Made me change to a a single tap with two fingers in one app because the delay is really annoying.

You could work around the delay if your single click action is undoable or cancelable: do the action when click count == 1, and if click count == 2, revert the action of the single click. Might result in undesired/unexpected UI behavior, though (from a user perspective).