Snapshot widget state when syncing

Summary

We should snapshot the widget state when syncing state from the frontend to the kernel, since the sync may happen asynchronously because of the throttling.

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Original issue

hi

we have simple code in nglview that works fine with ipywidgets 5.2.2. However, there is no effect if using mode.set(...) in 6.0.0.beta5 version.

one example:

this.model.set('camera_str', JSON.stringify(this.stage.viewer.camera))

will not update camera_str in Python. https://github.com/arose/nglview/blob/master/js/src/widget_ngl.js#L77-L82

[jasongrout]

Okay, for now, how about you change it to:

class NGLWidget(DOMWidget):
    _view_name = Unicode("NGLView").tag(sync=True)
    _view_module = Unicode("nglview-js-widgets").tag(sync=True)
    _model_name = Unicode("DOMWidgetModel").tag(sync=True)
    _model_module = Unicode("jupyter-js-widgets").tag(sync=True)

[jasongrout]

I’ll work on the ipywidgets end - making it so that the syncing takes a snapshot of the state when you ask it to sync, and getting the state updates merging to work.

@hainm - this is now done in #1270, so I’ll close this issue. If you can try on current master, can you see if it helps your issue? (If not, we should be releasing a beta soon that you can try with.)