在调用performSegue之前，我如何检查是否所有照片都上传到了防火墙

Question

我正在制作一张表格，上传3-4张照片到火柴仓库。在上传完所有照片后，我想要执行一个segue

self.performSegue(withIdentifier: "createClubToClubDetail", sender: self)

在打电话给performSegue之前，我如何检查是否所有的照片都被上传到了火场。

将上面的代码放在for循环之后不能工作，因为上传照片在不同的线程中运行(?)

let storageRef = Storage.storage().reference(forURL: "xxxxx.appspot.com").child("club_photo").child(clubRef.key)

            for p in selectedImage {
                let imageData = UIImageJPEGRepresentation(p.value, 0.005)
                let storageImgRef = storageRef.child(p.key + ".jpg")
                storageImgRef.putData(imageData!, metadata: nil) { (metadata, error) in
                    if error != nil {
                        print(error!)
                        return
                    }
                    let downloadURL = metadata?.downloadURL()?.absoluteString
                    var photoRef: DatabaseReference!
                    if p.key == "main" {
                            photoRef = ref.child("photo").child(clubRef.key).child("main")
                    }
                    if p.key == "sub1" {
                        photoRef = ref.child("photo").child(clubRef.key).child("sub1")
                    }
                    if p.key == "sub2" {
                        photoRef = ref.child("photo").child(clubRef.key).child("sub2")
                    }
                    if p.key == "sub3" {
                        photoRef = ref.child("photo").child(clubRef.key).child("sub3")
                    }

                    photoRef.setValue(downloadURL)
                    print("Upload photo: \(p.key)")


                }

            }


 self.performSegue(withIdentifier: "createClubToClubDetail", sender: self)

Answer 1

如前所述，标准的DispatchGroup API能够为您的问题提供一个很好的解决方案。由于您可能在应用程序的其他地方也需要此功能，所以我尝试将基于DispatchGroup的解决方案封装在一个很好的助手类中：

//
// UploadTracker.swift
//

import Foundation 
import FirebaseDatabase

class UploadTracker {
    private let group = DispatchGroup()

    fileprivate func trackSetValue(_ value: Any?, ref: DatabaseReference) {
        group.enter()
        ref.setValue(value) { (error, _) in
            assert(error != nil, "\(error)")
            self.group.leave()
        }
    }

    func uploadDidFinish(block: @escaping () -> Void) {
        group.notify(queue: .main) { block() }
    }
}

extension DatabaseReference {
    func setValue(_ value: Any?, trackedBy tracker: UploadTracker) {
        tracker.trackSetValue(value, ref: self)
    }
}

在您的原始代码中，其用法是：

let uploadTracker = UploadTracker()
for p in selectedImage {
    ...
    photoRef.setValue(downloadURL, trackedBy: uploadTracker)
}
uploadTracker.uploadDidFinish {
    self.performSegue(withIdentifier: "createClubToClubDetail", sender: self)
}

Answer 2

我已经尝试了下面的代码上传多个图像，并在上次上传完成后执行segue，虽然这是一个临时修复，但它有效。

当用户希望将多个映像保存到firebase存储时，将调用saveToServerButtonPressed方法。selectedImages是UiImage类型的数组，具有用户希望上载的所有图像。保留var counter仅仅是为了捕获最后一个图像的成功上传，这样用户就可以导航到其他屏幕/任何其他任务，而这些任务只有在所有上传完成之后才能完成。

@IBAction func saveToServerButtonPressed(_ sender: Any) {
    var counter = 0
    for image in selectedImages {
        uploadImage(image, progressBlock: { (progressValue) in
            self.progressStatus.text = "\(progressValue)%"
        }) { (downloadUrl, error) in
            if error == nil {
                if let downloadUrl1 = downloadUrl
                {
                    counter += 1
                    self.imagesUrls.append(downloadUrl1)
                    if counter == self.selectedImages.count {
                        self.performSegue(withIdentifier: "showDownloadedSegue", sender: self)
                    }
                }
            } else {
                print("Error Occured \(String(describing: error))")
            }
        }
    }
}

方法，该方法将图像实际上载到firebase上。

func uploadImage(_ image: UIImage, progressBlock: @escaping (_ percentage: Double) -> Void, completionBlock: @escaping (_ url: URL?, _ errorMessage: String?) -> Void) {
    let storage = FIRStorage.storage()
    let storageReference = storage.reference()
    let imageName = "\(Date().timeIntervalSince1970).jpg"
    let imagesReference = storageReference.child(imageName)

    if let imageData = UIImageJPEGRepresentation(image, 0.8) {
        let metadata = FIRStorageMetadata()
        metadata.contentType = "image/jpeg"
        let uploadTask = imagesReference.put(imageData, metadata: metadata, completion: { (metadata, error) in
            if let metadata = metadata {
                completionBlock(metadata.downloadURL(), nil)
            } else {
                completionBlock(nil, error?.localizedDescription)
            }
        })
        uploadTask.observe(.progress, handler: { (snapshot) in
            guard let progress = snapshot.progress else {
                return
            }
            let percentage = (Double(progress.completedUnitCount) / Double(progress.totalUnitCount)) * 100
            progressBlock(percentage)
        })
    } else {
        completionBlock(nil, "Image couldn't be converted to Data.")
    }
}
}

注意:这段代码在Swift 4上运行良好