Swift - 从 UserDefaults 检索数据后，TableView 中不显示任何数据

Question

我正在尝试获取已保存的数据，然后将其加载到TableView中。目前，如果我第一次保存对象，数据将被正确编码、保存、解码、读取和显示。但是，如果键已存在并且我正在添加到现有数据中，则 TableView 中不会显示任何内容。

这是我目前在第一个视图控制器中保存它的方式：

let userEntry = UserEntries(date: String(todayDate), questions: [UserEntries.Question(question: q1Text, answer: q1Answer), UserEntries.Question(question: q2Text, answer: q2Answer)])
var allEntries : [UserEntries] = []
if doesKeyExist(key: "allEntries") == true {
let jsonDecoder = JSONDecoder()
if let data = UserDefaults.standard.data(forKey: "allEntries"),
let userEntries = try? jsonDecoder.decode(UserEntries.self, from: data) {
allEntries = [userEntries]
}
allEntries.insert(userEntry, at: 0)
let jsonEncoder = JSONEncoder()
if let value = try? jsonEncoder.encode(allEntries) {
UserDefaults.standard.set(value, forKey: "allEntries")
UserDefaults.standard.synchronize()
}
} else {
let jsonEncoder = JSONEncoder()
if let value = try? jsonEncoder.encode(userEntry) {
UserDefaults.standard.set(value, forKey: "allEntries")
UserDefaults.standard.synchronize()
}
}
let newViewController = storyboard?.instantiateViewController(withIdentifier: "tabViewController") as! UITabBarController
present(newViewController, animated: true, completion: nil)
}

这就是我在表格视图中显示它的方式

var TableData : [UserEntries] = []
override func viewDidLoad() {
super.viewDidLoad()
let jsonDecoder = JSONDecoder()
if let data = UserDefaults.standard.data(forKey: "allEntries"),
let userEntries = try? jsonDecoder.decode(UserEntries.self, from: data) {
print(userEntries.date)
TableData = [userEntries]
}
// Uncomment the following line to preserve selection between presentations
// self.clearsSelectionOnViewWillAppear = false
// Uncomment the following line to display an Edit button in the navigation bar for this view controller.
// self.navigationItem.rightBarButtonItem = self.editButtonItem
}
override func numberOfSections(in tableView: UITableView) -> Int {
return 1
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return TableData.count
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "entryCell", for: indexPath)
cell.textLabel?.text = TableData[indexPath.row].date
cell.detailTextLabel?.text = TableData[indexPath.row].questions[0].answer
return cell
}

我有一种感觉，这是在 TableView 中获取/显示数据的逻辑错误，但不确定它到底是什么/如何解决它。感谢您的帮助！

Answer 1

我不知道你的doesKeyExists函数是做什么的，但你可以通过以下方式改进你的数据操作：

let userEntry = UserEntries(date: String(todayDate), questions: [UserEntries.Question(question: q1Text, answer: q1Answer), UserEntries.Question(question: q2Text, answer: q2Answer)])
var allEntries : [UserEntries] = []
let jsonDecoder = JSONDecoder()
if let data = UserDefaults.standard.data(forKey: "allEntries"),
let userEntries = try? jsonDecoder.decode([UserEntries].self, from: data) {
allEntries = userEntries
}
allEntries.insert(userEntry, at: 0)
let jsonEncoder = JSONEncoder()
if let value = try? jsonEncoder.encode(allEntries) {
UserDefaults.standard.set(value, forKey: "allEntries")
UserDefaults.standard.synchronize()
}
let newViewController = storyboard?.instantiateViewController(withIdentifier: "tabViewController") as! UITabBarController
present(newViewController, animated: true, completion: nil)
}

控制器的问题在于您只保存了一个条目UserDefaults.尝试将代码更改为

let jsonDecoder = JSONDecoder()
if let data = UserDefaults.standard.data(forKey: "allEntries"),
let userEntries = try? jsonDecoder.decode([UserEntries].self, from: data) {
print(userEntries)
TableData = userEntries
}