Swift 4中通过TextField计算年龄的代码报错问题求助

Hey there! Let's fix this age calculation code step by step—your error comes from a few syntax mistakes, incorrect API usage, and unsafe force unwraps that we can clean up easily.

First, let's break down the root cause of your error #

The Cannot assign to immutable expression of type "NSCalenda..." error is directly from this broken line:

let cal = NSCalendar? = NSCalendar(calendarIdentifier: .gregorian)

This is invalid syntax—you're trying to assign an optional type to a let constant in a messed-up way. Plus, in Swift 4+, we should use the native Calendar type instead of NSCalendar whenever possible.

Here's the fixed, robust version of your code #

I've also added safety checks to avoid crashes from bad input or invalid dates:

@IBAction func profilSettings(_ sender: AnyObject) {
    // 1. Safely get the birth date string from the TextField
    guard let dobString = self.dob.text, !dobString.isEmpty else {
        self.myage.text = "Please enter a valid date"
        return
    }
    
    // 2. Set up a DateFormatter to parse the input string (adjust dateFormat to match your TextField's expected format)
    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "dd-MM-yyyy" // Use "yyyy-MM-dd" if input is like "2000-01-01"
    dateFormatter.locale = Locale(identifier: "en_US_POSIX") // Prevents locale-based parsing issues
    
    // 3. Convert the string to a Date object
    guard let dobDate = dateFormatter.date(from: dobString) else {
        self.myage.text = "Invalid date format"
        return
    }
    
    // 4. Calculate the age using Calendar's built-in date difference method
    let calendar = Calendar(identifier: .gregorian)
    let now = Date()
    let ageComponents = calendar.dateComponents([.year], from: dobDate, to: now)
    
    // 5. Safely display the age
    if let age = ageComponents.year, age >= 0 {
        self.myage.text = String(age)
    } else {
        self.myage.text = "Invalid birth date"
    }
}

Key improvements I made: #

• Removed broken NSCalendar declaration: Replaced it with the correct Swift Calendar initialization.
• Replaced manual string splitting: Using DateFormatter is way more reliable than splitting strings—it handles invalid formats gracefully instead of crashing.
• Eliminated force unwraps: Used guard let to safely handle optional values, preventing crashes if the TextField is empty or the date is invalid.
• Used correct API for age calculation: calendar.dateComponents([.year], from:to:) is the proper way to calculate year differences between two dates in Swift 4+.

内容的提问来源于stack exchange，提问作者benji