Storing Global/Environment Variables in iOS Swift Apps - ios

Question

I'm a JavaScript web app developer that has just inherited a legacy iOS app. The app is full of hardcoded URLs that point to our production API.
I'd like to factor out the Base URL into a constants file, or an environment variables file, or a config file, so that a different Base URL can be used in different environments (dev, staging, production).
What's the best practice in the land of the Swift?
Is there something similar to a .env file I can use?

Answer 1

What I always do is probably a more flexible approach than checking constants in your code and littering different values of the same variable per environment everywhere.
It is not necessary to create .xcconfig files either.
Setting up the whole thing is a little more work but you will see that it is very easy to use afterwards.
In my example you see how I set different REST endpoints for production/UITest/development builds in my Toeppersee iOS app.
Changes to your Info.plist
First, just define a new constant and select a name that identifies your content, in my case it is TS_WEBSERVICE_URL:
Make sure to set its value to the name you chose, enclosed in $() (brackets, not braces!), in my case it's $(TS_WEBSERVICE_URL).
Build settings
In your build settings tab, add custom "user defined" build parameters, again with the same name:
You see that you can define values for Debug, UITests and Release. And that I use this mechanism for a whole lot of things that are different in the environments.
Adding more environments
If you need more environments, add them on your master project node's Info tab (like I probably did here with UITests):
Use the values in code
Now for the easy part: use your newly defined values in your code. It all boils down to getting an NSBundle instance and reading the value defined in your Info.plist which has been substituted automatically during build process.
Objective C:
NSString *webserviceURL = [[NSBundle mainBundle] objectForInfoDictionaryKey:#"TS_WEBSERVICE_URL"];
Swift:
let webserviceURL = Bundle.main.object(forInfoDictionaryKey: "TS_WEBSERVICE_URL") as! String
Just one line of code per environment setting.
One thing I have not shown, but which is also fairly easy: just define a category to NSBundle and supply new methods called webserviceUrl and similar methods. They can then be called like this: Bundle.main.webserviceUrl() which even more simplifies the source code.
Edit: write extension to Bundle object (optional)
To achieve the aforementioned simplified access to the webservice URL, a new Swift file is created and called (for example): Bundle+AppAdditions.swift
import Foundation
// An extension (or category in Objective C) extends any types functionality,
// in our case the NSBundle foundation class.
extension Bundle {
// get the webservice URL from an NSBundle instance
public func webserviceUrl() -> String {
// get an object for info dictionary key and cast it as string
return self.object(forInfoDictionaryKey: "TS_WEBSERVICE_URL") as! String
}
}
The extension works directly on any given Bundle instance, not necessarily only the main bundle. Example:
let url = Bundle.main.webserviceUrl()
or any other bundle, e.g. for an App Clip Extension containing an InitialViewController:
let url = Bundle(for: InitialViewController.self).webserviceUrl()
I would actually add another static extension method to get the app clip extension bundle. But that's optional as well ;-)

Answer 2

Some recommend creating a config file (.xcconfig) for every environment and then you can set up your different base URL there.
Where I used to work, we used a constants file where we set up different values, urls,ports and so on depending on the environment like this:
#if DEBUG
let a = 2
#if PRODUCTION
let a = 4
I think this is the best thing to do.