What's difference between NSPhotoLibraryAddUsageDescription and NSPhotoLibraryUsageDescription?

Question

My app get crashed today while updating on Xcode9, testing on iOS11. After adding NSPhotoLibraryAddUsageDescription then it works, even i already had NSPh

Answer 1

To answer the last question on my own:

You need to declare both NSPhotoLibraryUsageDescription and NSPhotoLibraryAddUsageDescription to get it WORKS on both iOS 9, 10.3 and 11.

Technically it's different. I used to not declare NSPhotoLibraryUsageDescription, it works fine on iOS 9 and 11 but failed and crashed on iOS 10.3.

This is a really bad version controlling from Apple while higher version doesn't comply and support older version permission.