如何在执行完成之前等到从 Firebase 存储下载完成 swift

Question

在以下从 Firebase 存储下载图像的模型中，它完成了 for 循环，但完成块中的打印语句显示“[]”。然而，片刻之后下载到达并显示在数组中。如何在执行完成之前等待图像完全下载并进入数组并稍后重新加载 table？

查看模型：下载图像


    //Firebase Cloud Storage Reference:
    let storage = Storage.storage()
    
    public var imageArray: [UIImage] = []

    public func fetchProductImages(completion: @escaping (Result<UIImage, Error>) -> Void) {
        
        //Clear Image Array:
        imageArray.removeAll()
        
        for imageRef in products! {
            
            //Access to Image inside a Collection:
            let storageRef = self.storage.reference(withPath: imageRef.image!)
            
            //Download in Memory with a Maximum Size of 1MB (1 * 1024 * 1024 Bytes):
            storageRef.getData(maxSize: 1 * 1024 * 1024) { [self] data, error in
                
                if let error = error {
                    //Error:
                    print (error)
                    
                } else {
                    
                    //Image Returned Successfully:
                    let image = UIImage(data: data!)

                    //Add Images to the Array:
                    imageArray.append(image!)
                    
                }
            }
        }
        
        print (imageArray)
        
        completion (true)
        
    }

Answer 1

由于加载图像数据是一个异步操作，任何需要在图像加载后运行的代码都需要在完成处理程序中，从那里调用，或者以其他方式同步。

一个简单的方法是统计加载完成的图片数量，然后调用once it matches the length of the数组：

imageArray.removeAll()

for imageRef in products! {
    
    let storageRef = self.storage.reference(withPath: imageRef.image!)
    
    storageRef.getData(maxSize: 1 * 1024 * 1024) { [self] data, error in
        
        if let error = error {
            print (error)                
        } else {
            
            //Image Returned Successfully:
            let image = UIImage(data: data!)

            //Add Images to the Array:
            imageArray.append(image!)

            // 
            if (imageArray.count == products!.count) {    
                completion (true)                
            }           
        }
    }
}

如何在执行完成之前等到从 Firebase 存储下载完成 swift

How to wait till download from Firebase Storage is completed before executing a completion swift

firebase

swift

firebase-storage