Using the output of a function in another function? - swift

Question

i have a fetch request and i want to use the result to inform other functions. the fetch is
func getExercises() {
guard let managedObjectContext = managedObjectContext else { return }
let userExercise = UserExercise(context: managedObjectContext)
let request: NSFetchRequest<UserExercise> = UserExercise.fetchRequest()
request.predicate = NSPredicate(format: "usersroutine == %#", self.routineName)
do {
let appDelegate = UIApplication.shared.delegate as! AppDelegate
let context = appDelegate.persistentContainer.viewContext
let queryResults = try context.fetch(request)
print ("num of results = \(queryResults.count)")
for exercise in queryResults as [NSManagedObject] {
print("Exercise NAME: \(exercise.value(forKey: "name"))")
}
} catch {
print("Error with request: \(error)")
}
The other functions are (capitals added where id want the output to be):
func configure(_ cell: TodaysRoutineTableViewCell, at indexPath: IndexPath) {
let userExercise = THE GET EXERCISE FUNCTIONS OUTPUT(at: indexPath)
and another:
fileprivate func updateView() {
var hasUserExercises = false
if let UserExercise = THE GET EXERCISE FUNCTIONS OUTPUT {
hasUserExercises = UserExercise.count > 0
}
I thought perhaps id just add queryResults in there and it would be fine, but as thats local to that function i just get errors. Whats the correct way to achieve this?
updated to show errors image
// MARK: - COREDATA FETCH
func getExercises(completion: (([NSManagedObject]?, NSError?) -> Void)?) {
guard let managedObjectContext = managedObjectContext else { return }
let userExercise = UserExercise(context: managedObjectContext)
let request: NSFetchRequest<UserExercise> = UserExercise.fetchRequest()
request.predicate = NSPredicate(format: "usersroutine == %#", self.routineName)
do {
let appDelegate = UIApplication.shared.delegate as! AppDelegate
let context = appDelegate.persistentContainer.viewContext
let exercises: [NSManagedObject]?
do {
let queryResults = try context.fetch(request)
print(queryResults)
for exercise in queryResults as [NSManagedObject] {
print("Exercise NAME: \(exercise.value(forKey: "name"))")
}
completion(exercises, nil)
} catch {
print("Error with request: \(error)")
completion(exercises, error)
}
}
}

Answer 1

Use of unresolved identifier 'exercises'
Based on the code you have shown in the image, reason for you first error is that, you have used the property exercises which is not declared yet. exercises in your completion closure's argument will not be accessible within that function. Its a parameter that needs to be passed to that closure.
When you call the completion block, you will have to pass an array of NSManagedObject to it which you construct after you fetch the results. In your case, construct an array within that for..in loop and call the completion block after that loop.
let exercises: [NSManagedObject]?
do {
let queryResults = try context.fetch(request)
print(queryResults)
for exercise in queryResults as [NSManagedObject] {
//Using the result, build the exercises array here
}
completion(exercises, nil)
} catch {
print("Error with request: \(error)")
completion(exercises, error)
}
Nil is not compatible with expected argument type '[NSManagedObject]'
This is because exercises argument is not an optional but you are passing nil to it. You will have to make the exercises argument as optional to take both non-nil and nil values. Change your method signature to below:
func getExercises(completion: ((exercises: [NSManagedObject]?, error: NSError?) -> Void)?)
Note: Make sure you handle nil appropriately in your completion closure you pass to the getExercises function.

Answer 2

Being fetch something that you could do in an async way, the right way would be to use a completion block (callbacks).
So your getExercises function could have a completion block parameter, for instance:
func getExercises(completion: ((exercises: [String], error: NSError?) -> Void)?)
Then, when your data is ready inside the getExercises function, you can invoke the completion block as follows:
completion?(exercises, error)
This question mark before completion is because the completion block is an optional parameter, so you could pass this block or not, up to you.
Maybe some update is required for Swift 3, just check the syntax for completion blocks.
Edit: You will need to pass a closure as an argument for your getExercises function when you call it:
getExercises(completion: { (exercises, error) in
//Do what you want with the result, this is the result of getExercises
print(exercises)
})
Now, inside getExercises you will pass the result to your closure:
func getExercises() {
// ...
do {
// ...
completion(exercises, nil)
} catch {
print("Error with request: \(error)")
completion?([], error)
}
}
Exercises will be of a certain type, not sure what you are handling there, I placed an array of String as example.