swift - 检查许多空参数？

Question

我有代码来检查一个空参数:

if let isEmpty = name?.isEmpty where isEmpty == false {

但是我需要实现代码来检查是否有很多是假的？例如数量、价格以及名称...我如何使用此代码获得此信息？

if let isEmpty = name?.isEmpty where isEmpty == false {
    if let isEmpty = total?.isEmpty where isEmpty == false {
        if let isEmpty = price?.isEmpty where isEmpty == false {
           if let isEmpty = quantity?.isEmpty where isEmpty == false {
            }
        }
    }
}

当我放置它们的列表时，当我在循环末尾执行 try catch 循环时，它不起作用。

@IBAction func saveItems(sender: AnyObject) {
    let name = txtName.text
    let total = txtTotal.text
    let price = txtPrice.text
    let quantity = stepperValue.text

    if let isEmpty = name?.isEmpty || 
          isEmpty = price?.isEmpty || 
          isEmpty = total?.isEmpty || 
          isEmpty = quantity?.isEmpty where isEmpty == false {

    }

    // Create Entity
    let entity = NSEntityDescription.entityForName("Item", inManagedObjectContext: self.managedObjectContext)

    // Initialize Record
    let record = NSManagedObject(entity: entity!, insertIntoManagedObjectContext: self.managedObjectContext)

    // Populate Record
    record.setValue(txtName, forKey: "name")
    record.setValue(txtTotal, forKey: "total")
    record.setValue(txtPrice, forKey: "price")
    record.setValue(stepperValue, forKey: "quantity")
    record.setValue(NSDate(), forKey: "date")

    do {
        // Save Record
        try record.managedObjectContext?.save()

        // Dismiss View Controller
        dismissViewControllerAnimated(true, completion: nil)

    } 
    catch {
        let saveError = error as NSError
        print("\(saveError), \(saveError.userInfo)")

        // Show Alert View
        showAlertWithTitle(title: "Warning", message: "Your message could not be saved", cancelButtonTitle: "OK")
    }

} 
else {
    // Show Alert View
    showAlertWithTitle("Warning", message: "Your to-do needs a name.", cancelButtonTitle: "OK")
}

Answer 1

一个解决方案是一个大的(但单一的，没有嵌套)、复杂的 if 语句:

if let name = name, total = total, price = price, quantity = quantity
    where !name.isEmpty && !total.isEmpty && !price.isEmpty && !quantity.isEmpty {

    // use name, total, price, quantity

}

<小时/>

另一种可以说是更好的解决方案是一次一个地解开它们，一步一步地为每个变量使用一个 guard 语句。

guard let name = name where !name.isEmpty else {
    // name is nil or empty
    return
}

guard let total = total where !total.isEmpty else {
    // total is nil or empty
    return
}

guard let price = price where !price.isEmpty else {
    // price is nil or empty
    return
}

guard let quantity = quantity where !quantity.isEmpty else {
    // quantity is nil or empty
    return
}

// use name, total, price, and quantity, all are non-nil, non-empty

<小时/>

当然，根据您在它们为 nil 或为空或不为空的情况下所做的操作，第一个解决方案可能最好使用 guard 编写:

guard let name = name, total = total, price = price, quantity = quantity
    where !name.isEmpty && !total.isEmpty && !price.isEmpty && !quantity.isEmpty else {

    // something was nil or empty
    return

}

// use name, total, price, quantity

<小时/>

如果我正在编写这段代码，假设nil或为空表示数据无法保存到数据库的状态，我会选择两个guard之一 方法，我选择哪种方法取决于我希望向用户传达的消息的描述性。