Swift-如何将图像保存到数组中并访问它们？

Question

I have a map that allows me to add pins (annotations) to it. When I click on a pin, the app goes to another view controller and shows images downloaded from online. I "save" these images to an array but later I cannot access them. For example, when I tap "Back" to go to the previous view controller and tap on the same pin from before, instead of showing the images I originally downloaded and saved, new images are downloaded from online. Essentially, the images in the array are replaced. How can I save the images and retrieve them? Sorry for long amounts of code, I shortened as much as I could.

This is my class for the images:

class Image {

    var image: UIImage

    init(image: UIImage) {
        self.image = image
    }
}

This is my class for the pins. Notice, an array of type Image from the Image class is in here:

class Pin: Hashable {

    var hashValue: Int {
        get {
            return "\(latitude.hashValue),\(longitude.hashValue)".hashValue
        }
    }

    let latitude: Double
    let longitude: Double
    var images = Array<Image>()

    init(latitude: Double, longitude: Double)
    {
        self.latitude = latitude
        self.longitude = longitude
    }
}

// must be declared in the global scope! and not just in the class scope
func ==(lhs: Pin, rhs: Pin) -> Bool
{
    return lhs.hashValue == rhs.hashValue
}

I add pins to a Set like so (no duplicates of pins allowed). Also, the selected pin is sent to the secondViewController:

class MapViewController: UIViewController, MKMapViewDelegate, UIGestureRecognizerDelegate {

var pins = Set<Pin>()

func mapView(mapView: MKMapView!, didSelectAnnotationView view: MKAnnotationView!) {
 // Add pin to set
            let selectedCoordinatePoint = Pin(latitude: latFromPin, longitude: lonFromPin)
            var select = "\(latFromPin.hashValue),\(lonFromPin.hashValue)".hashValue
            pins.insert(selectedCoordinatePoint)

        //Goto to next view controller and show data depending on the pin selected
        for pin in pins {
            if pin.hashValue == select.hashValue {

                dispatch_async(dispatch_get_main_queue()) {
                    let storyBoard = UIStoryboard(name: "Main", bundle: nil)
                    let secondViewController = self.storyboard!.instantiateViewControllerWithIdentifier("CollectionViewControllerID") as! CollectionViewController

                    secondViewController.pin = pin

                    self.navigationController?.pushViewController(secondViewController, animated: true)
                }
            }
        }
    }
}

I download images from online and append to an array on this secondViewController (I shortened the code here):

class CollectionViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, MKMapViewDelegate {

    var pin: Pin!

    override func viewWillAppear(animated: Bool) {


                if let photosArray = photosDictionary["photo"] as? [[String:AnyObject]] {
                    // println("photosArray  =  \(photosArray )")

                    var count = 0
                    for photo in photosArray {
                        // 6 - Grab 21 random images
                        if count <= 20 {
                            // Grabs 1 image
                            let randomPhotoIndex = Int(arc4random_uniform(UInt32(photosArray.count)))
                            let photoDictionary = photosArray[randomPhotoIndex] as [String:AnyObject]

                            // 7 - Get the image url
                            let imageUrlString = photoDictionary["url_m"] as? String
                            let imageURL = NSURL(string: imageUrlString!)

                            // 8 - If an image exists at the url, append to array
                            let imageData = NSData(contentsOfURL: imageURL!)
                            let finalImage = UIImage(data: imageData!)
                            var image = Image(image: finalImage!)
                            self.pin.images.append(image)
                            count += 1

                            println(self.pin.images.count)
                        }
                    }
                }
            }
}

Answer 1

I'm not I understand what your asking exactly...you are making network calls to populate your image array. If you just want to pass the image array from VC to VC, you can use prepareForSegue to pass the value.

If you want to pull these down and then store them locally you need to read up on persistence. For example you can use something like Core Data, Parse, Realm...I personally use Parse because of it's ease. This is a good tutorial along the lines of what you're doing I think. It uses Parse to store the image data: http://www.appcoda.com/instagram-app-parse-swift/