ios – 调用函数时swift中的EXC_BAD_ACCESS

import UIKit

class NewsTableViewCell: UITableViewCell {

@IBOutlet weak var postImageView: CustomImageView!
@IBOutlet weak var postTitleLabel:UILabel!
@IBOutlet weak var authorLabel:UILabel!
@IBOutlet weak var dateLabel: UILabel!

var article: Article? {
        didSet {
            postTitleLabel.text = article?.title
            authorLabel.text = article?.author
            dateLabel.text = article?.date

            setupArticleImage()
        }
}
func setupArticleImage() {
         postImageView.loadImageUsingUrlString("http://theblakebeat.com/uploads/873463.jpg")
}

此代码调用函数loadImageUsingUrlString,该函数位于我的extensions.swift文件中.为每个加载的表视图单元调用它以加载其图像. extensions.swift的代码如下.

import UIKit

let imageCache = NSCache()

class CustomImageView: UIImageView {

    var imageUrlString: String?

    func loadImageUsingUrlString(urlString: String) {
        imageUrlString = urlString

        let url = NSURL(string: urlString)

        image = nil

        if let imageFromCache = imageCache.objectForKey(urlString) as? UIImage {
        self.image = imageFromCache
        return
    }

    NSURLSession.sharedSession().dataTaskWithURL(url!,completionHandler: { (data,respones,error) in

        if error != nil {
            print(error)
            return
        }

        dispatch_async(dispatch_get_main_queue(),{

            let imageToCache = UIImage(data: data!)

            if self.imageUrlString == urlString {
                self.image = imageToCache
            }

            imageCache.setObject(imageToCache!,forKey: urlString)
        })

    }).resume()
}

}

预先感谢您的任何帮助.