如何将Double类型数组存入UserDefaults并在TableView持久化加载

Got it, let's get your transaction data sticking around between app launches! The issue here is that you're not persisting your moneySpentArray to UserDefaults correctly—luckily, this is a straightforward fix. Here's exactly how to implement it:

1. Define a Reusable Key (Avoid Typos!) #

First, create a constant for your UserDefaults key somewhere accessible (like at the top of your ViewController). This prevents accidental typos when saving/loading:

private let moneySpentArrayKey = "SavedMoneySpentTransactions"

2. Load the Array When the App Starts #

In your viewDidLoad() (or wherever you initialize your array), pull the saved data from UserDefaults. We'll use a default empty array to handle the first launch case where no data exists yet:

override func viewDidLoad() {
    super.viewDidLoad()
    // Load saved array, default to empty if no data exists
    moneySpentArray = UserDefaults.standard.array(forKey: moneySpentArrayKey) as? [Double] ?? []
    // Don't forget to reload your TableView here to show the saved data
    tableView.reloadData()
}

3. Save the Array After Updating It #

When your addToMoney function updates the array (after the user taps Submit), immediately save the updated array to UserDefaults. Add this to your IBAction or directly in addToMoney:

@IBAction func submitButtonTapped(_ sender: UIButton) {
    // Get the user's input (add validation here to avoid invalid numbers!)
    guard let inputText = amountTextField.text, let newAmount = Double(inputText), newAmount > 0 else {
        // Show an error alert if input is invalid
        let alert = UIAlertController(title: "Invalid Amount", message: "Please enter a valid positive number.", preferredStyle: .alert)
        alert.addAction(UIAlertAction(title: "OK", style: .default))
        present(alert, animated: true)
        return
    }
    
    // Update your array
    addToMoney(amount: newAmount)
    
    // Save the updated array to UserDefaults
    UserDefaults.standard.set(moneySpentArray, forKey: moneySpentArrayKey)
    // Explicit synchronize is optional in modern iOS, but it's safe to include for older versions
    UserDefaults.standard.synchronize()
    
    // Refresh the TableView to show the new entry
    tableView.reloadData()
    
    // Clear the text field for next input
    amountTextField.text = ""
}

func addToMoney(amount: Double) {
    moneySpentArray.append(amount)
    // Add any other logic you need here (like formatting, sorting, etc.)
}

Quick Notes to Avoid Headaches #

• Validation: Always validate user input before adding it to your array—this prevents nil values or negative amounts from breaking your data.
• UserDefaults Limits: Keep in mind that UserDefaults is meant for small amounts of data (like user preferences or short transaction lists). If you plan to store hundreds/thousands of transactions later, you might want to switch to Core Data or a local database like Realm.
• Type Safety: The as? [Double] ?? [] cast ensures you get a valid Double array even if the saved data is corrupted or missing.

内容的提问来源于stack exchange，提问作者Coding while Loading