如何确保在加载数据之前不访问数据? [英] How to ensure make sure I´m not accessing data until it´s loaded in?
问题描述
我是编程新手,我的代码收到以下错误:致命错误:在解开Optional值时意外发现nil 2017-10-27 16:06:16.755817 + 0200 Inspireme1.0 [836:85307]致命错误:展开一个可选值时意外发现nil (lldb)
I´m new at programming and I my code gets the error: fatal error: unexpectedly found nil while unwrapping an Optional value 2017-10-27 16:06:16.755817+0200 Inspireme1.0[836:85307] fatal error: unexpectedly found nil while unwrapping an Optional value (lldb)
新错误: 致命错误:索引超出范围 2017-10-27 19:08:05.488502 + 0200 Inspireme1.0 [1262:771572]致命错误:索引超出范围 (lldb)
New error: fatal error: Index out of range 2017-10-27 19:08:05.488502+0200 Inspireme1.0[1262:771572] fatal error: Index out of range (lldb)
我已经在这里查看了,但是我不知道如何在我的情况下应用此方法:如何确保在装入插座之前不访问插座
I already looked it up here but I don´t know how to apply this in my case: How to ensure I'm not accessing outlets before they're loaded in
这是我的代码:
var quotes: RandomItems! = RandomItems([
"Jonas",
"Mary",
"Michael",
"Jeff",
"Sarah",
])
@IBAction func PresentText(_ sender: Any) {
PresentingLabel.text = quotes.next() //<-- Error
}
struct RandomItems: Codable
{
var items : [String]
var seen = 0
init(items:[String], seen: Int)
{
self.items = items
self.seen = seen
}
init(_ items:[String])
{ self.init(items: items, seen: 0) }
mutating func next() -> String
{
let index = Int(arc4random_uniform(UInt32(items.count - seen)))
let item = items.remove(at:index) //<--Error
items.append(item)
seen = (seen + 1) % items.count
return item
}
func toPropertyList() -> [String: Any] {
return [
"items": items,
"seen": seen
]
}
}
var randomItems: RandomItems?
override func viewDidAppear(_ animated: Bool) {
// Code to load the struct again after the view appears.
let defaults = UserDefaults.standard
quotes = defaults.codable(RandomItems.self, forKey: "quotes")
}
override func viewWillDisappear(_ animated: Bool) {
// Code to save struct before the view disappears.
let defaults = UserDefaults.standard
if let quotes = quotes {
defaults.set(codable: quotes, forKey: "quotes")
}
}
}
推荐答案
报价不应是可选的.
您需要在viewDidAppear中处理可选结果,而不是假设引号始终会解开.
You need to handle the optional outcome in viewDidAppear rather than assuming quotes will always unwrap.
quotes = defaults.codable(RandomItems.self,forKey:"quotes")?? RandomItems([])
quotes = defaults.codable(RandomItems.self, forKey: "quotes") ?? RandomItems([])
在viewDidLoad中:
In viewDidLoad:
defaults.set(codable: quotes, forKey: "quotes")
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