Regular expressions with textedit?

[saward]

Hi! I'm wondering what would be a good option for applying a regular expression/pattern match to a textedit, so that users can't enter text other than that allowed?

I think I could do this by checking the response for changed(), but in that case there's a slight flicker because presumably there's a frame where the text is changed, before I revert it to the last permitted state. I can live with the flicker, but interested to know if there's a better approach.

[emilk]

There are two situations to consider:

• Allowed character (e.g. only entering numbers)
• Allowed formats (e.g. only allowing valid email addresses)

For the first case, I think we should add a filter to what characters TextEdit accepts, i.e. just a Fn(char) -> bool passed to one of the TextEdit builder functions. If the users tried to enter characters outside this filter, they won't be accepted.

For the second case, I think it is better to leave the validation to the egui user. How to respond to invalid input depends highly on the situation - sometimes you want to color the TextEdit red, or show an error text next to it.

[saward]

Hi, thanks for answering! My situation is a bit more complex, like the email case (in my case, ensuring, e.g., that money entered has no more than one decimal). I could do the validation and provide an error rather than prohibit invalid input. I think that's a great approach that would work with egui in its current form.

Thinking about changes to egui, I had been thinking of a way to pass a regular expression to TextEdit, and if the newly entered character would not match the regex then it would reject that character. Similar to the first solution you propose, except passing a regex instead of character filters. Do you think that would be a useful solution?

[emilk]

A character filter of the form Fn(char) -> bool is more general than a regex, but more importantly it does not require egui to depend on the enormous regex crate.

[saward]

Ah, maybe I misunderstood the filter option. So the user would provide a function of the form Fn(char) -> bool, and then it would be used to decide whether to reject a character or not? And therefore, the user (such as myself) could use a regex inside that provided function?

[emilk]

yup

[saward]

Sounds like it would do the trick then!

[Mingun]

Probably it is better to use a Pattern trait for this, but right now it is nightly-only