从 cmets 看来，如果您的视图尚未加载，并且您的某些视图仍然是 nil。您的应用程序崩溃，因为在 limitLabel.text = limit[0].limitSum 行中，limitLabel 是 nil。即使调用limitLabel.text = "Hello world!"
，它也会崩溃，无论 Realm
您始终可以保护您需要避免更改代码的数据。只需添加
guard let limitLabel = limitLabel else { return nil }
guard let ForThePeriod = ForThePeriod else { return nil }
等等。
我尝试稍微清理一下您的代码。很难理解您到底想达到什么目标，但类似以下的内容可能看起来更合适：
func leftLabels() {
// Elements needed for method to execute.
guard let limitLabel = limitLabel else { return }
guard let forThePeriodLabel = forThePeriodLabel else { return }
guard let availableForSpendingLabel = availableForSpendingLabel else { return }
// Items that will be reused throughout the method later on
let limits: [Limit]
let firstLimit: Limit
let dates: (start: Date?, end: Date?)
let filterLimit: Int
limits = self.realm.objects(Limit.self)
guard limits.isEmpty == false else { return }
firstLimit = limits[0]
// limitLabel
limitLabel.text = firstLimit.limitSum
// Date components
dates = {
let calendar = Calendar.current
let formatter = DateFormatter()
formatter.dateFormat = "yyyy/MM/dd HH:mm"
let firstDay = firstLimit.limitDate as Date
let lastDay = firstLimit.limitLastDate as Date
let firstComponent = calendar.dateComponents([.year, .month, .day], from: firstDay)
let lastComponent = calendar.dateComponents([.year, .month, .day], from: lastDay)
let startDate = formatter.date(from: "\(firstComponent.year!)/\(firstComponent.month!)/\(firstComponent.day!) 00:00")
let endDate = formatter.date(from: "\(lastComponent.year!)/\(lastComponent.month!)/\(lastComponent.day!) 23:59")
return (startDate, endDate)
}()
// forThePeriodLabel
filterLimit = realm.objects(SpendingDB.self).filter("self.date >= %@ && self.date <= %@", startDate ?? "", endDate ?? "").sum(ofProperty: "cost")
forThePeriodLabel.text = String(filterLimit)
// availableForSpendingLabel
availableForSpendingLabel.text = {
guard let a = Int(firstLimit.limitSum) else { return "" }
let b = filterLimit
let c = a - b
return String(c)
}()
}
注意一些有助于更好地构建和解决代码的做法。
- 首先保护危险数据
- 为您的方法创建一个可重复使用的项目列表（应该尽可能少，在大多数情况下没有）。请注意以后如何分配这些。如果你在分配给它之前尝试使用它，你的编译器会警告你。
- 将尽可能多的代码包装到封闭的部分，例如
availableForSpendingLabel.text = { ... code here ... }()
- 使用元组，例如
let dates: (start: Date?, end: Date?)
- 不要害怕使用长名称，例如
availableForSpendingLabel
我什至会进一步尝试将其分解为多种方法。但是我不确定这个方法是做什么的，并假设你只发布了它的一部分......
========== 编辑：添加替代方法 ==========
来自 cmets，这是一个金融应用程序，因此至少处理 Decimal 数字可能是有意义的。还引入了添加一种在内部解析数据的新结构的方法。格式化程序也用于格式化数字。以及其他一些改进：
struct Limit {
let amount: Decimal
let startDate: Date
let endDate: Date
}
struct Spending {
let cost: Decimal
let date: Date
}
struct LimitReport {
let limitAmount: Decimal
let spendingSum: Decimal
let balance: Decimal
init(limit: Limit) {
let limitAmount: Decimal = limit.amount
let spendingSum: Decimal = {
let calendar = Calendar.autoupdatingCurrent // Is this OK or should it be some UTC or something?
func beginningOfDate(_ date: Date) -> Date {
let components = calendar.dateComponents([.day, .month, .year], from: date)
return calendar.date(from: components)!
}
let startDate = beginningOfDate(limit.startDate)
let endDate = calendar.date(byAdding: .day, value: 1, to: startDate)
let spendings: [Spending] = realm.objects(Spending.self).filter { $0.date >= startDate && $0.date < endDate }
return spendings.reduce(0, { $0 + $1.cost })
}()
let balance = limitAmount - spendingSum
self.limitAmount = limitAmount
self.spendingSum = spendingSum
self.balance = balance
}
}
func leftLabels() {
// Elements needed for method to execute.
guard let limitLabel = limitLabel else { return }
guard let forThePeriodLabel = forThePeriodLabel else { return }
guard let availableForSpendingLabel = availableForSpendingLabel else { return }
guard let limit = self.realm.objects(Limit.self).first else { return }
let formatter = NumberFormatter()
formatter.numberStyle = .currency
formatter.currencySymbol = "$"
let report = LimitReport(limit: limit)
limitLabel.text = formatter.string(from: report.limitAmount)
forThePeriodLabel.text = formatter.string(from: report.spendingSum)
availableForSpendingLabel.text = formatter.string(from: report.balance)
}