Add a continuous_update option for text widgets

[jasongrout]

The sliders have a continuous_update option that only triggers a value change when the user stops dragging a slider: https://github.com/ipython/ipywidgets/blob/master/ipywidgets/widgets/widget_int.py#L155. Likewise, the text boxes should have an option to only update the value when the text box is blurred, or maybe when the user presses enter in a one-line textbox (sort of the equivalent of the on_submit handler textboxes currently have).

[dhirschfeld]

An event which triggers on enter or when a user leaves the text box would be useful. The current on_submit can be confusing if the user forgets to press enter, the text has changed but the handler hasn't triggered so the text in the box won't necessarily be related to the state of the widget.

Or perhaps some sort of validation to highlight the fact that the text has changed but the change hasn't been submitted yet.

[jasongrout]

+1 to the UI indication of a 'dirty' textbox.

[codypiersall]

+1 for this! I wrote a notebook that uses ipywidgets to control a motor, and had to use a Text widget because the hardware would ignore commands while it was already doing something. But a BoundedFloatText was conceptually better! @dhirschfeld's idea is perfect -- update when the box loses focus or the user hits the return key.

Would a pull request implementing this be likely to be merged?

[jasongrout]

Would a pull request implementing this be likely to be merged?

Yes, very likely!

[codypiersall]

I'd love to work on this, but if someone else wants to please go ahead! I probably won't have time for about the next month, but after I'm done with my current side project I'll give this a whirl. All this to say...

If someone comes across this post in about a month and I haven't re-posted, feel free to ping me!

[jasongrout]

Thanks! I've also marked it as sprint-friendly, so it'll be easier for new contributors to find.

[jasongrout]

ping @codypiersall, as requested. Someone else just asked for this today too.

[jasongrout]

To implement this, I would:

1. Make a continuous_update attribute analogous to the slider's attribute at

   ipywidgets/ipywidgets/widgets/widget_int.py

   Line 161 in 673e42d

   continuous_update = Bool(True, help="Update the value of the widget as the user is holding the slider.").tag(sync=True)

   on the textboxes (

   ipywidgets/ipywidgets/widgets/widget_string.py

   Line 73 in 673e42d

   class Text(_String):

   ,

   ipywidgets/ipywidgets/widgets/widget_string.py

   Line 61 in 673e42d

   class Textarea(_String):

   ,

   ipywidgets/ipywidgets/widgets/widget_float.py

   Line 63 in 673e42d

   class FloatText(_Float):

   ,

   ipywidgets/ipywidgets/widgets/widget_float.py

   Line 80 in 673e42d

   class BoundedFloatText(_BoundedFloat):

   , and the inttext widgets too)
2. In the javascript code to each of the views, handle continous updates with the input event, and non-continuous updates with the change event.