Question

我有三个条件：

data.weight和myoutput均为nil
myoutput没有价值

data.weight和myoutput都有一个值

override func viewWillAppear(_ animated: Bool) {
    super .viewWillAppear(animated)
    self.navigationItem.hidesBackButton = true

    let myOutput = UserDefaults.standard.string(forKey: "height")
    let dateFormator = DateFormatter()
    dateFormator.dateFormat = "dd.MM.yyyy"
    let data = WeightTracker.mr_findFirst(with: NSPredicate(format: "date == %@", dateFormator.string(from: Date()))) as? WeightTracker

    if myOutput == nil && data?.weight == nil {
        bmiLabel.text = "--"
    } else if myOutput == nil && data?.weight != nil {
        bmiLabel.text = "--"
    } else {
        let dateFormator = DateFormatter()
        dateFormator.dateFormat = "dd.MM.yyyy"
        if let data = WeightTracker.mr_findFirst(with: NSPredicate(format: "date == %@", dateFormator.string(from: Date()))) as? WeightTracker {
            let myOutput: AnyObject? = UserDefaults.standard.object(forKey: "height") as AnyObject
            var sum = (myOutput as! NSString).doubleValue / 1000
            let total1 = sum * sum
            let total = Double(Int(data.weight!)!) / total1
            let dye = total/100.00
            bmiLabel.text = String(dye)
        }
    }
}

仅应针对第三个条件计算总和。处理此问题的正确方法是什么？

Answer 1

if let myOutput = UserDefaults.standard.string(forKey: "height") as? NSString , let weight = data?.weight {
    let dateFormator = DateFormatter()
    dateFormator.dateFormat = "dd.MM.yyyy"
    if let data = WeightTracker.mr_findFirst(with: NSPredicate(format: "date == %@", dateFormator.string(from: Date()))) as? WeightTracker{
        var sum = myOutput.doubleValue   / 1000
        let total1 = sum * sum
        let total = Double(Int(weight)!) / total1
        let dye = total/100.00

        bmiLabel.text = String(dye)
    }
} else {
    bmiLabel.text = "--"
}

Answer 2

你为什么不走相反的路

if myOutput != nil && data?.weight != nil {
    // Your logic here
}
else {
    bmiLabel.text = "--"
}

或者也可以将if完全替换为if-let，以提供安全的拆包并摆脱可选的链条和/或强制拆包

if let myOutput = myOutput, let weight = data?.weight {
    // Your logic here
}
else {
    bmiLabel.text = "--"
}

或者，如果您想提供早期逃生，那么您甚至可以使用guard-let

guard let myOutputUnwrapped = myOutput, let weight = data?.weight else {
    bmiLabel.text = "--"
    return 
}

    /* Your logic here */

if-let和guard-let的优点是您已经获得了可使用的未包装值，因此您不必担心变量中的!和?

如果其他条件正确，如何处理多个？

2 个答案: