How can I pass a GET query param into my server side APEX controller?

Question

Background: I am trying to redirect a user from an external site to my salesforce visualforce page with a GET query param as part of the URL. (This is part of a managed package)

I want that parameter to be passed to my apex code so that I can do stuff with it on the server-side (after validating that it is what I expect, etc. of course).

What I have tried so far:

https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_System_PageReference_getParameters.htm

https://developer.salesforce.com/docs/atlas.en-us.pages.meta/pages/pages_variables_global_currentpage.htm

Unfortunately, I haven't been able to see the get param in my apex code using either of those strategies.

I am concerned that there may have been a change to how query params work in the Summer '19 update (https://releasenotes.docs.salesforce.com/en-us/spring19/release-notes/rn_forcecom_general_namespace_prefix_cruc_reminder.htm) so that they don't get passed through, even if I am using a namespaced get param. (I tried both the c__ and the <my managed package namespace>__, but other than continuing to see the param in the address bar, it hasn't helped.

In particular, when doing a sanity check, even though I can see the get param in the address bar after visiting the page, I noticed that I can't get the get parameter to be available to javascript running in the VF page:

When I go to https://<scratch org namespace>.lightning.force.com/lightning/n/MyCustomPage?mypackagenamespace__parameter=helloworld

I would expect to be able to see the mypackagenamespace__parameter param get printed to the console using this javascript:

<script>
   window.onload = function(){
            console.log(window.location.search);
   }
</script>

But instead, I am seeing a completely different URL and set of SFDC parameters:

?sfdc.tabName=<SFDC id>&vfRetURLInSFX=%2Fhome%2Fhome.jsp&ltn_app_id=<SFDC id>&nonce=<nonce code>&sfdcIFrameOrigin=https://<scratch org namespace>.lightning.force.com&tour=&isdtp=p1&sfdcIFrameHost=web&clc=0

Now for my question:

Does anyone know why this is happening and how I can make it so that my GET param can be appropriately passed through to make it to my server-side code?

---

Update: I just tried to go to https://<scratch org namespace>.visualforce.com/apex/MyCustomPage?mypackagenamespace__parameter=helloworld instead of the lightning/n/MyCustomPage version and it worked.

Is there a way to make it work with the original URL, or do I just need to make sure to adjust the URL target to use the apex/MyCustomPage format?

Answer 1

My understanding, based on a previous question and implementation I did, is that one cannot pass parameters to a Visualforce page when the page is targeted via a Lightning Named Tab URL (i.e., under /n/).

Instead, you do have to use the apex/MyCustomPage URL, which does allow parameters to reach the Visualforce page controller.