Swift / Firestore：预加载图片

Question

我正在尝试将Firestore中的图像预加载到模型中

class Post_ {
var postID: String?
var fromUser: DocumentReference?
var toUsers: [DocumentReference] = []
var type: String?
var post: Any? <- To This
var timer: Int?
var createdAt: Timestamp?
}

以便我可以显示而不必等待它加载。

这就是我从Firestore中提取它的方式：

extension Post_ {
static func transform(id: String, dict: [String: Any]) -> Post_ {
    return Post_(
        postID: id,
        fromUser: dict["fromUser"] as! DocumentReference,
        toUsers: dict["toUsers"] as! [DocumentReference],
        type: dict["type"] as! String,
        post: UIImage(data: Functions.getData(url: dict["post"] as! String))!,
        timer: dict["timer"] as! Int,
        createdAt: dict["createdAt"] as! Timestamp
    )
}
}

这就是我要尝试的方法，但它一直崩溃

static func getData(url: String) -> Data {
    var post: Data?

    URLSession.shared.dataTask(with: URL(string: url)!) { (data, res, error) in
        if let e = error {
            print(#function + ": " + e.localizedDescription)
        } else {
            if let d = data {
                post = d
            }
        }
    }
    if let p = post {
        return p
    } else {
        return Data()
    }
}

但这不起作用。一直崩溃，说没错