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Re: JavaFX: Bindings, StringConverters, and ChangeListeners

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Nigel Wade <nmw@ion.le.ac.uk> writes:

Hi Nigel,

> The first thing I'd suggest is to think about the problem from the
> user's perspective rather than the programmer's.
>
> If I, as a user, enter a number into a text field and inadvertently
> enter an invalid character, I'd be rather annoyed if the GUI element
> wiped out what I'd entered and replaced it with something which I
> didn't want.  It would be better from my (user) perspective if the
> text element warned me of my transgression (flash, highlight, red
> background whatever) and left my text there for me to edit, rather
> than make me enter it again with the likelihood of making a similar
> mistake again.

Oh, flashing is actually a nice idea and can be done pretty easily from
my listener.

> Imagine if the current contents were 002324561234, and I wanted to
> change it to 002324560234 but instead changed it to 00232456O234. Your
> current method would revert it back to 002324561234, and I may never
> notice that my change had been overridden.

Well, in the concrete case the number is the maximum number of matches
to be looked for in a database, so the numbers aren't that hard to
distinguish but I got your point.

> What's wrong with parsing the entered text and, if there is an
> exception, catch it and display some feedback, leaving the focus on
> the text field? If you really, really want to set the text back to the
> original value you could still do that in the catch block. I don't see
> any benefit from using a ChangeListener.

The problem is that I have no control over when and where the string in
the text field is parsed and converted to a number.  I just specified a
declarative binding between the text field's text property and an
integer property with a standart converter and thereby gave up exact
control over these things.  But bindings are such an integral part of FX
that I guessed there must be some standart way to treat invalid input so
that the binding's converter doesn't err.

Bye,
Tassilo

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Thread

JavaFX: Bindings, StringConverters, and ChangeListeners Tassilo Horn <tsdh@gnu.org> - 2016-06-22 15:18 +0200
  Re: JavaFX: Bindings, StringConverters, and ChangeListeners Nigel Wade <nmw@ion.le.ac.uk> - 2016-06-22 15:22 +0100
    Re: JavaFX: Bindings, StringConverters, and ChangeListeners Tassilo Horn <tsdh@gnu.org> - 2016-06-23 08:39 +0200
      Re: JavaFX: Bindings, StringConverters, and ChangeListeners Martin Gregorie <martin@address-in-sig.invalid> - 2016-06-23 09:59 +0000
        Re: JavaFX: Bindings, StringConverters, and ChangeListeners Nigel Wade <nmw@ion.le.ac.uk> - 2016-06-23 12:19 +0100
      Re: JavaFX: Bindings, StringConverters, and ChangeListeners Nigel Wade <nmw@ion.le.ac.uk> - 2016-06-23 12:39 +0100
        Re: JavaFX: Bindings, StringConverters, and ChangeListeners Tassilo Horn <tsdh@gnu.org> - 2016-06-23 14:39 +0200
  Re: JavaFX: Bindings, StringConverters, and ChangeListeners Eric Douglas <e.d.programmer@gmail.com> - 2016-06-22 08:06 -0700
    Re: JavaFX: Bindings, StringConverters, and ChangeListeners Tassilo Horn <tsdh@gnu.org> - 2016-06-23 08:45 +0200
      Re: JavaFX: Bindings, StringConverters, and ChangeListeners Eric Douglas <e.d.programmer@gmail.com> - 2016-06-23 05:11 -0700
        Re: JavaFX: Bindings, StringConverters, and ChangeListeners Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-23 08:22 -0400
          Re: JavaFX: Bindings, StringConverters, and ChangeListeners Tassilo Horn <tsdh@gnu.org> - 2016-06-23 15:12 +0200
            Re: JavaFX: Bindings, StringConverters, and ChangeListeners Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-23 10:56 -0400

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