Add support for callbacks

[drew]

Currently users must poll a 'readyToUse' flag in order to use a dynamically added definition. By adding support for callback, they can be assured their projection has loaded already. I have added a simple enhancement to the constructor API to support this.

This will, however, not capture the case of failing to load a definition (which is another enhancement needed).

The API looks like this new Proj4js.Proj( projCode, callback );

The callback is pushed into a queue, when defsLoaded is run it activates these callbacks. A more advanced AJAX promise object would be ideal, but may be overkill.

[drew]

Is there a date for milestone 1.0.2. Perhaps I could lend some assistance to adding this feature. I believe I have written a better version of this diff that is working well for us internally.

[madair]

Drew this patch looks good and I don't have a timeline for 1.0.2 but this patch is worth a new release. I can do a new release when I get back from vacation in July.

[drew]

Thanks for getting back to me.

I've fixed a bug in this patch, I'll get this submitted on Monday (I've forgotten how I made the diff). We had some wrapping logic for the Proj constructor that is no longer needed with my new patch.

[drew]

As promised, attached updated version of queueing. There is still an issue that if multiple calls are made for a Projection before any finish, that this projection will be called multiple times. Unfortunately, a clean solution to this problem would take a serious refactor of the library. I have a hack in my client code to workaround this problem.

[drew]

proj4js.diff

[madair]

I'm having trouble with this diff file because it seems to be generated against a local svn copy (e.g. there is no diff line in the Proj constructor that includes the callback argument) and I'm afraid of missing something. Can you re-generate the patch against the trunk version of proj4js.js or attach the whole file and I can diff against trunk from that?

[drew]

custom version of proj4js w/callbacks

[drew]

Sorry I was probably using the official release instead of trunk. Here's the entire file we're using. Let me know if I need to merge trunk and test again.

[madair]

the patch file shows what would be committed, seems to work for me now. Can you see if I missed anything?

[drew]

I noticed there's a bug with the queue. Each time a Proj is created it should instantiate it's own queue. this.queue =[] will do that, so these lines should be removed: 515-522.

[madair]

fixed at rev [2069]

also used this mechanism in the test page

Thanks for the contribution!

[madair]

slight change to the patch, only call the callbacks after projection code init

[drew]

Not sure why I tested the queue twice probably chasing a bug I didn't fully understand. All of our unit tests passed, this changes looks good on my side.

Thanks for getting this in so fast!