swift - fatal error : unexpectedly found nil while unwrapping an Optional value. Swift

Question

我是 Swift 的新手。我的问题是我不确定如何展开可选值。当我打印 object.objectForKey("profile_picture") 时，我可以看到 Optional(<PFFile: 0x7fb3fd8344d0>) .

    let userQuery = PFUser.query()
    //first_name is unique in Parse. So, I expect there is only 1 object I can find.
    userQuery?.whereKey("first_name", equalTo: currentUser)
    userQuery?.findObjectsInBackgroundWithBlock({ (objects: [PFObject]?, error: NSError?) -> Void in
        if error != nil {
        }
        for object in objects! {
            if object.objectForKey("profile_picture") != nil {
                print(object.objectForKey("profile_picture"))
                self.userProfilePicture.image = UIImage(data: object.objectForKey("profile_pricture")! as! NSData)
            }
        }
    })

Answer 1

您将使用 if let 来执行“可选绑定(bind)”，仅当相关结果不是 nil 时才执行 block (并绑定(bind)变量 profilePicture 到进程中的解包值)。

它会是这样的:

userQuery?.findObjectsInBackgroundWithBlock { objects, error in
    guard error == nil && objects != nil else {
        print(error)
        return
    }
    for object in objects! {
        if let profilePicture = object.objectForKey("profile_picture") as? PFFile {
            print(profilePicture)
            do {
                let data = try profilePicture.getData()
                self.userProfilePicture.image = UIImage(data: data)
            } catch let imageDataError {
                print(imageDataError)
            }
        }
    }
}

或者，如果你想异步获取数据，也许:

userQuery?.findObjectsInBackgroundWithBlock { objects, error in
    guard error == nil && objects != nil else {
        print(error)
        return
    }
    for object in objects! {
        if let profilePicture = object.objectForKey("profile_picture") as? PFFile {
            profilePicture.getDataInBackgroundWithBlock { data, error in
                guard data != nil && error == nil else {
                    print(error)
                    return
                }
                self.userProfilePicture.image = UIImage(data: data!)
            }
        }
    }
}

这将是沿着这些思路的东西，使用 if let 来解包那个可选的。然后您必须获取与 PFFile 对象关联的 NSData(来自 getData 方法或 getDataInBackgroundWithBlock，大概)。

参见 Optional Binding The Swift Programming Language 中的讨论。