Support eager formatting

[steven-spiel]

This is a great plugin. Thank you for simplifying TextInputFormatters.

One feature request is to have eager formatting

Given this configuration for date formatting:

MaskTextInputFormatter(
  mask: '##/##/####',
  filter: <String, RegExp>{'#': RegExp('[0-9]')},
),

I would expect that upon entering 01, that the text field would add the formatting so it read 01/. Reason being, if a user was really trying to enter in / after the 01, the text field doesn't allow them to do that, which could be frustrating.

Is that doable? I think the trickiest bit might be that when using backspace, we wouldn't want to add the / on every text input event, or they'd never be able to delete any of the formatting. So there'd need to be some way to compare the state of the text before/after the change.

[KevinZhang19870314]

@steven-spiel Hi any solution or workaround for this? I am now facing the same requirement!

[steven-spiel]

@KevinZhang19870314 We ended up just writing our own formatter

[harkairt]

Same issue, we'd like to have
##h ##m ##s but the trailing s won't appear