IBOutlet nil after instantiateViewControllerWithIdentifier

问题

Not sure exactly what I'm doing wrong here. I've listed out what my problem is and my code. Would love to get some help.

Thanks!

Problem:

• VC1 presents VC2.
• IBOutlets from VC1 are now nil.
• VC2 dismisses back into VC1.
• IBOutlets in VC1 are still nil.

VC1 loads a grid of pictures from flickR. VC2 has a searchBar controller, when VC2 is dismissed it does runs flickR query. Right before my self.collectionView.reload() fails because self.collectionView is nil :(

VC1

import UIKit

class MainViewController: UIViewController, UICollectionViewDelegate,    UICollectionViewDataSource {

@IBOutlet var collectionView: UICollectionView!
@IBOutlet var searchMask: UIView!

let api_key = "f87357398a52b80e0c9f76bf94c8ee94"

var flickResults:NSMutableArray! = NSMutableArray()
var titleResults:NSMutableArray! = NSMutableArray()

override func viewDidLoad() {
    super.viewDidLoad()
     loadPhotos("Brasil")
    // Do any additional setup after loading the view.
}

override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)
}

func loadPhotos(searchString: String) {
    let flickr:FlickrHelper = FlickrHelper()
    println("Collection: \(self.collectionView)")
    flickr.request(searchString, per_page: 50, completion: { (searchStr, flickrPhotos, photoTitle) -> () in
        dispatch_async(dispatch_get_main_queue(), {
            self.flickResults = flickrPhotos
            self.titleResults = photoTitle
            self.collectionView.reloadData()
        })
    })
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

override func preferredStatusBarStyle() -> UIStatusBarStyle {
    return UIStatusBarStyle.LightContent
}


func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {

    let cell: PhotoCell = self.collectionView.dequeueReusableCellWithReuseIdentifier("photoCell", forIndexPath: indexPath) as PhotoCell
    cell.photoImageView.alpha = 0
    let queue:dispatch_queue_t = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)

    dispatch_async(queue, {
        let searchURL: String = self.flickResults.objectAtIndex(indexPath.item) as String
        let title: String = self.titleResults.objectAtIndex(indexPath.item) as String
        let image: UIImage = self.loadImage(searchURL)
        dispatch_async(dispatch_get_main_queue(), {
            UIView.animateWithDuration(0.5, animations: {
                cell.photoImageView.image = image
                cell.photoTitle.text = title.capitalizedString
                cell.photoImageView.alpha = 1
            })

        })
    })

    insertBlurView(cell.titleMask, UIBlurEffectStyle.Dark)

    return cell
}

func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return self.flickResults.count
}

func loadImage(imageUrl: String) -> UIImage{
    let url = NSURL(string: imageUrl)
    let data = NSData(contentsOfURL: url!)
    let image = UIImage(data: data!)
    return image!
}


@IBAction func searchButtonPressed(sender: UIButton) {
    let storyboard = UIStoryboard(name: "Main", bundle: nil);
    let vc: SearchViewController = storyboard.instantiateViewControllerWithIdentifier("Search") as SearchViewController
    providesPresentationContextTransitionStyle = true
    definesPresentationContext = true
    vc.modalPresentationStyle = UIModalPresentationStyle.OverCurrentContext
    self.presentViewController(vc, animated: false, completion: nil)

}
}

VC2

 import UIKit


 class SearchViewController: UIViewController, UITextFieldDelegate, UISearchBarDelegate, UICollectionViewDelegate {


@IBOutlet var searchMask: UIView!
@IBOutlet var searchField: UITextField!
@IBOutlet var searchBar: UISearchBar!

override func viewDidLoad() {
    super.viewDidLoad()
    insertBlurView(self.searchMask, UIBlurEffectStyle.Dark)
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

@IBAction func exitTap(sender: UIButton) {
    self.dismissViewControllerAnimated(true, completion: nil)
}


func searchBarSearchButtonClicked(searchBar: UISearchBar) {
    self.dismissViewControllerAnimated(true, completion: {
        let mainvc = self.storyboard?.instantiateViewControllerWithIdentifier("Main") as MainViewController
        mainvc.loadPhotos(searchBar.text)
    })
  }
}

回答1:

Thanks to rdelmar, I was able to figure this out using protocols.

Here's what I added:

• SearchDelegate
• SearchDelegate function runSearch()

VC1

class MainViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, SearchDelegate {  

func runSearch(searchString: String) {
    loadPhotos(searchString)
 }

}

VC2

protocol SearchDelegate {
    func runSearch(searchString: String)
 }

class SearchViewController: UIViewController, UITextFieldDelegate, UISearchBarDelegate, UICollectionViewDelegate {


@IBOutlet var searchMask: UIView!
@IBOutlet var searchField: UITextField!
@IBOutlet var searchBar: UISearchBar!

var delegate: SearchDelegate?

func searchBarSearchButtonClicked(searchBar: UISearchBar) {
    delegate?.runSearch(searchBar.text)
    self.dismissViewControllerAnimated(true, completion:nil)

}

来源：https://stackoverflow.com/questions/28732084/iboutlet-nil-after-instantiateviewcontrollerwithidentifier