Is there a way to handle double-click as single-click?

Anvil Q&A
#1

What I’m trying to do:
Prevent users from double-clicking my buttons and links. This is a habit of some users, outside of my control. (Complain to Microsoft as to how they got into this habit.)

Double-clicking activates most links/buttons twice, which does not always end well. This should be treated as a single-click, unless specified otherwise.

I have hundreds of links and buttons, so adding code to every single one of their event-handlers is not an attractive solution.

If there’s no global solution, I might try creating a decorator (proposed name: @debounce) to do the job. If the same event is triggered more than once within a second or so, it would ignore the second triggering. I’d still have to use it in over a hundred places, but it’s better than coding it longhand.

1 Like
#2

Rather than debounce the handlers in form code, you might consider overriding the Button/Link classes add_event_handler method

from functools import wraps
from time import sleep

orig_add_event_handler = Button.add_event_handler
DELAY = 0.3

def debounce(fn):

    clicks = []
    
    @wraps(fn)
    def wrapped(*args, **kws):
        if clicks:
            return
        clicks.append(True)
        try:
            fn(*args, **kws)
        finally:
            sleep(DELAY)
            clicks.pop()

    return wrapped

def add_event_handler(self, event, handler):
    if event == "click":
        handler = debounce(handler)
    return orig_add_event_handler(self, event, handler)

Button.add_event_handler = add_event_handler
2 Likes
Handle double clicks on buttons
#3

Patching the Button class this way is something I don’t normally think of, coming from a C++ background. Thanks!

And I could revert to the decorator approach if my app needs finer control. With some links/buttons, for example, it might suffice simply to disable the control until the handler returns.

Edit: Luckily, this problem has reared its head in only one spot in my code, so I was able to keep the scope of the change very small. But I’ll keep this tactic on hand, for worse cases.

#4

Thank you for bringing this up! Huge headache of mine I didn’t bring to the forum :slight_smile:

I wrap my functions with the following

button.enable = False
#DO EVENT STUFF HERE
button.enable = True

But that is not full proof.

#5

Yes, that is not foolproof. If an exception is raised, it will never reach the button.enable = True line.

A With Statement Context Manager would do the job, though, in those cases.

1 Like
#6

Could the “wait_for_writeback” decorator work?

https://anvil-extras.readthedocs.io/en/latest/guides/modules/utils.html#wait-for-writeback

#7

I haven’t looked at Anvil Extras in any detail yet. However, in my immediate case, writeback is not involved.