Swift version: 5.10
Here's an easy win for you that will make your apps immediately much better: NSCache
is a specialized class that behaves similarly to a mutable dictionary with one major difference: iOS will automatically remove objects from the cache if the device is running low on memory.
Helpfully, if the system does encounter memory pressure NSCache
will automatically start to remove items without you knowing about it, which means you won't get a memory warning unless even more RAM needs to be cleared. It will also remove items intelligently, trying to keep as much cached as possible.
Here's how to use it, imagining a fictional class called ExpensiveObjectClass
that you want to compute as infrequently as you can:
let cache = NSCache<NSString, ExpensiveObjectClass>()
let myObject: ExpensiveObjectClass
if let cachedVersion = cache.object(forKey: "CachedObject") {
// use the cached version
myObject = cachedVersion
} else {
// create it from scratch then store in the cache
myObject = ExpensiveObjectClass()
cache.setObject(myObject, forKey: "CachedObject")
}
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Available from iOS 4.0
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.
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