Ios 将相集数组快速转换为URL数组

我有一个

PHAssets的数组

，所以我想把它转换成

URL的数组

func getURL(ofPhotoWith mPhasset: PHAsset, completionHandler : @escaping ((_ responseURL : URL?) -> Void)) {
    let options: PHContentEditingInputRequestOptions = PHContentEditingInputRequestOptions()
    options.canHandleAdjustmentData = {(adjustmeta: PHAdjustmentData) -> Bool in
        return true
    }
    mPhasset.requestContentEditingInput(with: options, completionHandler: { (contentEditingInput, info) in
        completionHandler(contentEditingInput!.fullSizeImageURL)
    })
}


func getUrlsFromPHAssets(assets:[PHAsset], completion: @escaping ((_ urls:[URL]) -> ())){
    var arrUrl:[URL] = []
    for asset in assets {
        self.getURL(ofPhotoWith: asset) { (url) in
            arrUrl.append(url!)
        }
    }
    completion(arrUrl)
}

我在main中调用下面的函数

self.getUrlsFromPHAssets(assets: assets, completion: { (urls) in
            print(urls)
}) 

因此，在函数

getUrlsFromPHAssets

中，如何等待将URL附加到URL数组的循环完成，然后返回它

更新函数

getUrlsFromPHAssets

：

---

更新函数后，结果似乎正常，但我不确定它是否会在任何时候更正。

在第二个函数中，您使用

for

循环来执行一系列异步函数。每当您有多个异步函数，它们的完成都像这样相互依赖时，您可能需要一个

DispatchGroup

。此对象可以调用

enter（）

，以指示异步块正在启动，并在异步块完成后调用

leave（）

func getUrlsFromPHAssets(assets: [PHAsset], completion: @escaping ((_ urls:[URL]) -> ())) {
    var array: [URL] = []
    let group = DispatchGroup()
    for asset in assets {
        group.enter()
        self.getURL(ofPhotoWith: asset) { (url) in
            // I changed this from force unwrapping.
            // Seems like it's totally possible to get back a nil URL,
            // in which case, you don't want to crash
            if let url = url {
                array.append(url)
            }
            group.leave()
        }
    }
    // This closure will be called once group.leave() is called
    // for every asset in the above for loop
    group.notify(queue: .main) {
        completion(array)
    }
}

---

我刚刚更新了我的函数，结果似乎还可以。但我不确定。你能检查一下吗？嗯。。。不，你更新的代码根本不起作用。您试图绕过这是一个异步函数的事实。非常感谢。我得到了它。

func getUrlsFromPHAssets(assets: [PHAsset], completion: @escaping ((_ urls:[URL]) -> ())) {
    var array: [URL] = []
    let group = DispatchGroup()
    for asset in assets {
        group.enter()
        self.getURL(ofPhotoWith: asset) { (url) in
            // I changed this from force unwrapping.
            // Seems like it's totally possible to get back a nil URL,
            // in which case, you don't want to crash
            if let url = url {
                array.append(url)
            }
            group.leave()
        }
    }
    // This closure will be called once group.leave() is called
    // for every asset in the above for loop
    group.notify(queue: .main) {
        completion(array)
    }
}