Change GeoJSON style_callback post-instantiation?

[deeplook]

When I add a GeoJSON layer like this:

m = Map(center=[38.8976, -77.0365], zoom=11)
gj = GeoJSON(data=open("my.geojson").read())
m.add_layer(gj)

I can change its style attribute later and the browser will apply the change:

gj.style = {"color": "red"}  # changes color from default to red

It would be very useful if the same would happen when "changing" the style_callback parameter" dynamically at any time later (and not only when instantiating the object) like this (setting it to a constant value only for illustration):

gj.style_callback = lambda feature: {"color": "green"}

But this has no effect now. I see that style_callback is not listed in gj.keyswhich is likely one part of the reason... I'm trying to understand if this would be possible or not.

[sackh]

@martinRenou - I would like to work on this for JupyterCon sprint. Please assign this to me.

[martinRenou]

Thank you!

[sackh]

Below is my analysis of this issue:

1. If we first set style_callback then it works as expected:

2. If we first set style trait and then style_callback then style will not change:

3. If we first set style trait and then data trait style will not change:

so when we set style trait it sets style in the javascript side. but when we set style_callback trait it updates data.
so once style trait is updated even if you update the style in data's properties then style of geojson does not change.
It looks like something from leaflet.js.after setting style trait and then changing data does not update style of the layer.

@martinRenou - can you help ?

[martinRenou]

I start to think this is not an issue.

The style property has precedence over the style_callback property. So if the same attribute (e.g. color) appears in both style and style_callback, then it's the one from style that is taken into account.

We should maybe just properly document this.

[sackh]

one more thing to note is that when we change the data trait of the GeoJSON we keep the same object and just clear the layer and add new data in the javascript side, as the object is the same its style is not changed even though we update data?
Also when changing the data creating a new GeoJSON object in the javascript side creates other problems that we faced earlier.

[sackh]

There is a similar issue #607, where style attributes are different still style, does not change.

[martinRenou]

So to be clear:

• style_callback actually changes the data
• style does not change the data, it overrides any style that was set on the data during the display
• hover_style does not change the data, it overrides any style that was set on the data during the display if the feature is hovered

[sackh]

Thanks, @martinRenou understood. I think we can close this one as well :)

[martinRenou]

Do you think this behavior makes sense? Should we rename those properties to make it clearer what they do?

Maybe it only needs extra documentation.

[sackh]

Yes will need to document these somewhere and yes definitely need to rename style_callback as it's not related to style but the data of the GeoJSON layer.

[martinRenou]

yes definitely need to rename style_callback as it's not related to style but the data of the GeoJSON layer

Makes sense! Can you think of a better name?

[deeplook]

Makes sense! Can you think of a better name?

Something like load_data?