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Lightning Components - New Tab, New You
Introduction
This is something I’ve been meaning to blog about for a while now, but things like Dreamforce, preparing for Dreamforce and the Winter 17 release kept getting in the way. I didn’t get as far as setting up a nice example, due to the sheer volume of code involved, so I haven’t been back and tried it out recently. Therefore it’s possible that you’ll never have the same experience I did, but as it’s not exactly onerous it seemed worth putting it out there anyway. Your mileage may vary.
Signature move
While building out the MVP for our BrightMedia Lightning booking page to demonstrate at Dreamforce, I needed to change the signature of one of my Apex controller methods, so to get a simple example from something like:
public static Account GetAccount(String idStr)
to
public static Account GetAccount(String idStr, String name)
and changed the parameters that the Lightning Component passed on the action from:
var params={idStr:'0018000001QtQVA', name:'Blog Post Account'};
That went well!
Once I’d made the various changes and saved all the artefacts, I refreshed the page and starting seeing some unexpected behaviour. The name parameter came through as null regardless of what I set it to. Debug statements in the lightning component showed that the name had a value (it wasn’t a hardcoded string unlike the example above!), but some time after I added it to the action it went bad. Making it a hardcoded string didn’t help, nor did juking around the other parameters. I even tried adding more parameters that definitely didn’t exist server side, but nothing helped.
After a some time and about and thousand debug statements later, I found that while I might be adding the new parameter to my params object, when that was sent to the server it had disappeared, hence the server always reported null.
Cache is king
I then tried what I should have as soon as this manifested itself, the browser equivalent of turning it off and on again. I closed the browser tab and opened a new one. Lo and behold everything worked as expected. We all know that the lightning framework aggressively caches on the front end to improve performance, and it looks like the client retained a metadata view of the server side signature after I changed it.
Now I need to stress that for once I’m not complaining about the behaviour of the framework! This is exactly the kind of thing that I’d expect when caching metadata. It’s not always possible to check everything in a cache is still valid - you quickly start to lose the benefit if you go back and check the source on every request.
The key takeaway here is that when your application involves caching and you change something which doesn’t work as you expected, open a new tab (or window), or even a new browser. It only takes a few seconds and will save time and heartache in the long run.
