【发布时间】：2017-01-24 21:53:24
【问题描述】：
我正在尝试让程序检查导航标题，然后相应地填充单元格。这对硬编码数组来说很容易，但使用 Core Data 对象会让事情变得很困难。
初始化程序 - 每个公司的 3 个产品和一个空数组，在检查页面标题后将它们设置为：
let defaultProductsApple = ["iPhone", "iPad", "Macbook"]
let defaultProductsGoogle = ["Search", "Firebase", "Magic Leap"]
let defaultProductsFacebook = ["Facebook", "Instagram", "WhatsApp"]
let defaultProductsTesla = ["Model S", "Model X", "PowerWall"]
let defaultProductsTwitter = ["Twitter", "Periscope", "Vine"]
var defaultProducts = [String]()
viewDidLoad - 检查页面标题并填充空数组，然后在删除时设置为 Core Data 以保持持久性：
override func viewDidLoad() {
super.viewDidLoad()
tableView.register(Cell.self, forCellReuseIdentifier: cellId)
// Navbar stuff
navigationItem.leftBarButtonItem = UIBarButtonItem(title: "Back", style: .plain, target: self, action: #selector(handleBackButton))
navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Add", style: .plain, target: self, action: #selector(handleAdd))
let entity = NSEntityDescription.entity(forEntityName: "Product", in: managedContext)!
switch self.navigationItem.title! {
case "Apple":
defaultProducts = defaultProductsApple
case "Google":
defaultProducts = defaultProductsGoogle
case "Twitter":
defaultProducts = defaultProductsTwitter
case "Tesla":
defaultProducts = defaultProductsTesla
case "Facebook":
defaultProducts = defaultProductsFacebook
default:
defaultProducts = defaultProductsApple
}
for productName in defaultProducts {
let product = NSManagedObject(entity: entity,insertInto: managedContext)
product.setValue(productName, forKey: "name")
products.append(product)
}
do {
try managedContext.save()
tableView.reloadData()
} catch let error as NSError {
print("Could not save. \(error), \(error.userInfo)")
}
}
最后在 cellForRow 中设置标签：
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: cellId, for: indexPath) as! Cell
let product = products[indexPath.row]
cell.textLabel?.text = product.value(forKey: "name") as? String
return cell
}
单元格在第一次尝试时会按应有的方式填充 - 即，如果我在上一个屏幕中点击“Apple”，单元格会显示 Apple 的 3 种产品。但是，如果我返回并点击“Google”，单元格现在会显示 Apple 的 3 款产品以及 Google 的 3 款产品，以此类推。
我怎样才能让cell.textLabel?.text = product.value(forKey: "name") as? String 只加载该公司的产品？
编辑：viewWillAppear 和 save 方法：
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
//1
guard let appDelegate =
UIApplication.shared.delegate as? AppDelegate else {
return
}
let managedContext =
appDelegate.persistentContainer.viewContext
//2
let fetchRequest =
NSFetchRequest<NSManagedObject>(entityName: "Product")
//3
do {
products = try managedContext.fetch(fetchRequest)
} catch let error as NSError {
print("Could not fetch. \(error), \(error.userInfo)")
}
}
func save(name: String) {
guard let appDelegate =
UIApplication.shared.delegate as? AppDelegate else {
return
}
let managedContext =
appDelegate.persistentContainer.viewContext
let entity =
NSEntityDescription.entity(forEntityName: "Product",
in: managedContext)!
let product = NSManagedObject(entity: entity,
insertInto: managedContext)
product.setValue(name, forKey: "name")
do {
try managedContext.save()
products.append(product)
} catch let error as NSError {
print("Could not save. \(error), \(error.userInfo)")
}
}
最终编辑 - 一次性设置所有默认值
// Default 5 companies at launch - user can delete/add/edit
func setDefaults() {
let userDefaults = UserDefaults.standard
let defaultValues = ["firstRun" : true]
userDefaults.register(defaults: defaultValues)
if userDefaults.bool(forKey: "firstRun") {
let defaultProducts = ["Apple" : ["iPhone", "iPad", "Macbook"],
"Google" : ["Search", "Firebase", "Magic Leap"],
"Facebook" : ["Facebook", "Instagram", "WhatsApp"],
"Tesla" : ["Model S", "Model X", "PowerWall"],
"Twitter" : ["Twitter", "Periscope", "Vine"]]
let companyEntity = NSEntityDescription.entity(forEntityName: "Company", in: managedContext)!
let productEntity = NSEntityDescription.entity(forEntityName: "Product", in: managedContext)!
// Setting the default company data (name, logo, and stockPrice)
let url = URL(string: "https://query.yahooapis.com/v1/public/yql?q=select%20symbol%2C%20Ask%2C%20YearHigh%2C%20YearLow%20from%20yahoo.finance.quotes%20where%20symbol%20in%20(%22AAPL%22%2C%22GOOG%22%2C%22TWTR%22%2C%22TSLA%22%2C%20%22FB%22)&format=json&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys")!
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
if error != nil {
print(error!)
} else if let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode == 200 {
let json = JSON(data: data!)
if let quotes = json["query"]["results"]["quote"].array {
for quote in quotes {
let symbol = quote["symbol"].stringValue
let name = NSLocalizedString(symbol, comment:"")
let ask = quote["Ask"].stringValue
let company = NSManagedObject(entity: companyEntity,insertInto: managedContext)
company.setValue(name, forKey: "name")
company.setValue(name, forKey: "logo")
company.setValue(ask, forKey: "stockPrice")
companies.append(company)
print(json)
}
// Setting the default products - should I be doing this here too?
let companyProducts = defaultProducts[companyName]
// iterate through all those products names...
for productName in companyProducts {
// create the corresponding Product:
let product = NSManagedObject(entity: productEntity,insertInto: managedContext)
// set its name attribute...
product.setValue(productName, forKey: "name")
// then set the relationship to the relevant Company...
product.setValue(company, forKey: "company")
}
DispatchQueue.main.async {
do {
try managedContext.save()
vc.tableView.reloadData()
userDefaults.set(false, forKey: "firstRun")
} catch let error as NSError {
print("Could not save. \(error), \(error.userInfo)")
}
}
}
} else {
print("The data couldn't be loaded")
}
}
task.resume()
}
}
【问题讨论】：
-
您是否有任何其他代码可以更新
products数组，可能是通过执行获取请求，例如。在viewWillAppear或其他生命周期方法之一？ -
@pbasdf 是的，我编辑了我的问题以包括
viewWillAppear以及save方法。任何帮助将不胜感激！ -
谢谢 - 这解释了你所观察到的。获取请求（在 viewWillAppear 中）获取所有内容；您需要一些方法来区分 Apple 的产品与 Google（以及其他所有人的）的产品。您可以通过向 Product 实体添加“公司”属性或向“公司”实体添加关系来做到这一点。您还需要修改代码以仅加载这些默认值一次。稍后我会添加完整的答案...
-
@pbasdf 谢谢，我会准备好在您发布该答案后立即投票！我刚刚开始学习 Core Data，所以这将是一次很棒的学习体验。我一直想在我的 Company 和 Product 实体之间添加关系，但不确定如何使用它或它对我有什么好处。如果有帮助，我已经发布了我的数据模型的屏幕截图。
标签： ios swift xcode uitableview core-data