add ability to use listeners

[greinacker]

Adds the ability to add listeners to charts. I realize you said this in the readme file:

For example, Methods and Events as described in Google Chart Tools’ API Docs, for use after a chart has been rendered, are not implemented because they felt more native being written as JavaScript functions, within views or .js files.

This totally makes sense; however, there isn't an easy way to "wire up" these javascript listeners when using this gem. The attached change is intended to be a generic way to attach callbacks to these charts, without (IMHO) violating the spirit of what you're talking about in the readme...

ref issue #38

[travisbot]

This pull request passes (merged 83d12c7 into 13c76cb).

[greinacker]

Some sample code that uses this:

my_chart.add_listener("select", "function() {chart_select_event(chart);}")

So not only can we add listeners, but we can also use the "chart" variable that's only available within the per-chart script, allowing us to use multiple charts on one page and be able to add listeners for each of them. In my own code, I also pass an ID identifying which chart it is to the callback, but this example gets the point across...

[szymon-jez]

+1
@greinacker This could not be done better. Please also don't forget to write about it in the documentation (README) ;)

[winston]

Happy to merge this in. But I am a little sad that it's not tested. =)

Let me know if you have time to get some tests in, else I'll merge it anyway and add in the tests in my free time.

Thank you!

[greinacker]

I too was a little sad when you pointed that out. Spec added. :-)

[fonteijne]

Hey there, I this works really easy. Just add one line and there is an event-listener! :)
The only thing I'm missing is some documentation for this. Am I just overlooking this, or is it really missing?
I would really want to get the selection.column name when I click on a table-field.
Is this already possible?
When calling this line:
"var selection = visualization.getSelection();" (from the Google Playground) it just stops.
So, is it possible to write some documentation for this feature?
Thank you in advance.

Fonteijne

[kandadaboggu]

@fonteijne refer to this reply for a sample usage: #36 (comment)

[winston]

You are right about the lack of documentation. Sorry about that.

I've raised a feature request fro it over on the docs repo. Will get to it soon.

winston/google_visualr_app#1

Thank you.

[fonteijne]

@kandadaboggu Thank you for the reference. Still struggling, but getting further.
I already launched an alert by clicking the graph. The graph is fully functioning.
But a table on the same page(!) is not doing the thing. Everywhere I click is '0'.
-- update
It seems like the wrong data_table is loaded. It (always) returns the value(!) of the first column. So, not the columnname, but the value of the first column.

@winston Thank you for the feature request. When I got it all figured out, maybe I can find the time to write a concept documentation for it. I'll keep you posted.