ios - 使用 Firebase 将图像从一个 View Controller 传递到另一个 View Controller (快速)

Question

我正在尝试将图像从一个 View Controller 传递到另一个 View Controller ，但在准备 segue 函数时出现错误

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {


        let post = posts[indexPath.row]

        if let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)as? collectionViewCellBooks {

            if let img = booksVC.imageCache.object(forKey: post.imageUrl as NSString) {
                cell.configureCell(post: post, img: img)
                return cell

        }else {

                cell.configureCell(post: post)
                return cell
            }
        }
            else {
                return collectionViewCellBooks()
            }

    }

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        self.performSegue(withIdentifier: "showImage", sender: self)
    }



    override func prepare(for segue: UIStoryboardSegue, sender: Any?)
    {

         if segue.identifier == "showImage"
         {

         let indexPaths = self.collectionView!.indexPathsForSelectedItems!
         let indexPath = indexPaths[0] as IndexPath
         let vc = segue.destination as! newViewController
        // vc.image = self.posts[(indexPath as NSIndexPath).row]
            vc.image = self.posts[indexPath.row]
         }





class newViewController: UIViewController {

    @IBOutlet weak var imageView: UIImageView!

    var image = UIImage()

    override func viewDidLoad() {
        super.viewDidLoad()

        self.imageView.image = self.image
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}

这是我的帖子类(class)

类(class)帖子{

private var _caption: String!
private var _imageUrl: String!
private var _postKey: String!



var caption: String {
    return _caption
}

var imageUrl: String {
    return _imageUrl
}

var postKey: String {
    return _postKey
}


init(caption: String, imageUrl: String) {

    self._caption = caption
    self._imageUrl = imageUrl
}

init(postKey: String, postData: Dictionary<String, AnyObject>) {

    self._postKey = postKey

    if let caption = postData["title"] as? String {
        self._caption = caption
    }
    if let imagesUrl = postData["imageURL"] as? String {
        self._imageUrl = imagesUrl
    }

}

title 和 imageURL 保存在 firebase 数据库中

Answer 1

您收到错误消息是因为您没有将图像发送到新的 viewController，而是发送了 Post 类的一个实例，顺便说一句，它甚至不包含图像(只有 imageURL)。您必须先从服务器中提取图像，然后才能在任何地方解析它。

您应该像现在一样解析整个帖子，并直接在新的 ViewController 中通过 postID 下载图像。 (如果您将图像保存在 Firebase 存储中)我总是最终解析整个对象，因为在开发的后期您可能决定在 newViewController 中显示更多属性。如果您解析了整个对象，则无需再更改代码结构。

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "your Identifier" {
            if let vc = segue.destination as?  NewViewController {
                if let post = sender as? Post {
                    vc.post = post
                }
            }
        }
    }

在您的 didSelectIdemAt 函数中，您需要更改 performSegue 函数的发送者:

 performSegue(withIdentifier: "your Identifier", sender: post)

现在你的 newViewController 有更多的代码，但我就是这样做的，它工作稳定。

let reference = FIRDatabase.database().reference()
reference.child("posts").child("<postID>").observeSingleEvent(of: FIRDataEventType.value, with: { (snapshot) in
print(snapshot.value)

if let snapshots = snapshot.children.allObjects as? [FIRDataSnapshot] {
    for snap in snapshots {

        if let postsDict = snap.value as? Dictionary<String, AnyObject> {

            if let imageURL = postsDict["imageURL"] as? String {
                let httpsReference = FIRStorage.storage().reference(forURL: imageURL)
                httpsReference.data(withMaxSize: 1 * 1024 * 1024, completion: { (data, error) in
                if error != nil {
                    print("error... couldn't get picture from Server \(error.localizedDescription)")
                    } else {
                        let image = UIImage(data: data!)
                        self.img = image! // you need to create this variable somewhere in your viewController Class before this code
                        //"your UIImageVIew.image" = img AND THAT IS IT
                    }
                }
            }
        }
    }
}