Im developing an SDK and its deployment target is set to 9.0. Im using some API's that are deprecated in iOS 10 and above and others that are deprecated at iOS 13 and above.
My question is what will happen to an app that is consuming my SDK and its deployment target is set to iOS 14? will my SDK be affected? will my methods get properly invoked? will it crash the hosting app? is the behaviour under these circumstances is unclear? or maybe all will run perfectly?
Any light on this would be appreciated, thanks.
First things first, deprecation is the first step in the process of ending the life of an API and Apple is warning the developers that these APIs will be removed in one of the future iOS releases. Nobody knows when except Apple. There is certainly a wisdom in that (e.g security concerns, better API design, etc).
Developing an SDK which uses deprecated APIs is generally considered a dead end. I am sure you have your own reasons, however, anyone who uses your SDK will be asking themselves whether there will be any value or will there be a maintenance overhead.
There are certain issues during the development stage that you should be aware of. If the app developer of an app who uses your SDK sets the deployment target to iOS14, most probably Xcode will flag this up as a warning. It depends on other things such as the development language that you are using, whether it is already compiled etc.
Assuming there is a good reason for you to move forward, there are several scenarios on what could happen.
In Production, the very short answer to your question is, the application will crash if the API is removed in the next OS upgrade by Apple (if the app developer doesn't take any action before it is released). However, long answer is a little bit more complicated than this.
The best case scenario is Apple doesn't remove the API for a very long time e.g UIWebView. I think it has been at least 5 years now since Apple deprecated the framework, and technical you can still build an app with the UIWebView. That means you do not have to do anything (in theory).
However, if the API is removed by the new OS update, there are several scenarios:
The device is eligible for an OS upgrade, THEN the app will most likely keep crashing when the API is called by the app/sdk.
If the device is NOT eligible for an OS upgrade (e.g stuck on iOS 10), the app will still live for a while on these devices until the owner buys a new device (whether the app developers takes action or not). That particular app version should also be available through iCloud purchases/downloads. So customers can re-download that version even if they delete it etc.
For an active app developer, the first scenario shouldn't happen. I would expect them to test the app on the next beta of the OS version and take action if there is an issue e.g ask you to provide an update, or replace your SDK with another one.
The API removal process can be a little bit more informed and Apple might force your hand, but be still gentle. Apple may make it explicit and warn developers that any new apps, or app updates which contain the API will not be accepted to App Store. This ties the app developers hands. They need to make a choice. This warning would be months in advanced and you would put this work into your backlog and plan for it.
The scenario in bullet point 2, on the other hand, may not be obvious at first, and Apple is doing a pretty good job of convincing the customers to buy the latest devices. There is a relative 2 year cycle, so you may not find many customer using older phones which are stuck on older OSs. This may be ignored depending on your significance level.
The app developers may or may not be able to keep the min target of the app. If they are so adamant then most likely their app will not be compatible with the latest devices or Apple may refuse their updates (as above). Then that means it is pretty much the end of life of the app, only used by a handful of customers.
There is also scenario where Apple may also remove the applications from App Store and iCloud download which are not maintained for a certain period of time (this has happened).