领域Swift筛选器多个ViewController

Question

Re-asking the question, here, with some modifications to the code:

I have a class called Galaxies, each with a list of Planets

class Galaxy: Object {
  let planets = List<Planet>()
}

class Planet: Object {
  dynamic var capitol = String()
  dynamic var council = String()
  dynamic var collective = String()
  dynamic var signals = String()
}

I have 10 viewcontrollers, each representing a galaxy with various planets particular to that galaxy. How can I filter for particular planets for a particular galaxy?

When I instantiate a Results<Galaxy>! instance with an implicitly unwrapped optional, it compiles in the first Galaxy VC because I have starter data in my AppDelegate. When I do this let galaxy = Results<Galaxy>? = nil let galaxy = Results<Galaxy>? = nil in the second Galaxy VC, the collection view goes blank.

This makes sense, because there is no data.

So, I guess I have two questions: how do I instantiate a Results object and filter for each view controller with no initial data?

I tried galaxies = realm.objects(Galaxy.self).filter("planets == %@", firstPlanet).sorted(byKeyPath: "capitol", ascending: false) in viewDidLoad() but this crashes:

libc++abi.dylib: terminating with uncaught exception of type NSException

Finally, var galaxy = Results<Galaxy>() raises an exception cannot invoke initializer for type Results with no arguments .

Answer 1

For Your View Controller A pass the planets from the selected Galaxy, prepare for segue method

var galaxies:[Galaxy] = realm.objects(Galaxy.self)
var selectedGalaxyIndex = 0
override func prepareForSegue(segue: UIStoryboardSegue!, sender: AnyObject!) {
    if (segue.identifier == "segue_for_ViewController_B") {
        // pass data to next view
        let vc = segue.destination as viewControllerB
        vc.planets = galaxies[selectedGalaxyIndex].planets
    }
}

In Your View Controller B add

var planets:[Planet]?

Answer 2

If there's no initial data, a Realm query will be empty, which appears to be what you want. For example:

class Galaxy: Object {
  let planets = List<Planet>()
}

class Planet: Object {
  dynamic var capitol = String()
  dynamic var council = String()
  dynamic var collective = String()
  dynamic var signals = String()
}

let realm = try! Realm()

let galaxies = realm.objects(Galaxy.self)
print(galaxies.count) // => 0

As for the NSException you're seeing, I suggest you read the whole message printed to the console or logs, as that should instruct you as to what you're doing wrong. From your code fragment, that might be that firstPlanet is nil, meaning that planets == nil is an illegal query, since a List property can never be nil.