使用 NotificationCenter Observer 处理异步请求
Using NotificationCenter Observer to Handle Asynchronous Requests
有人问过与此类似的问题,所以我深表歉意,但其中 none 对我有所帮助。
我正在努力 return 使用完成处理程序从这个异步请求到 Firebase 的值。我从 Firebase 检索的值是一个数组,它确实存在。但是
这是我向 Firebase 发出请求的函数:
class SearchManager {
var searchResults = [String]()
var listOfMosaics = [String]()
// Retrieves company list from Firebase
func getMosaicTitles(completionHandler: @escaping (_ mosaics: [String]) -> ()) {
Database.database().reference().child("mosaics").observeSingleEvent(of: .value, with: { (snapshot) in
guard let allMosaics = snapshot.value as? [String] else {
print("unable to unwrapp datasnapshot")
return
}
completionHandler(allMosaics)
})
}
// resets search results array
func resetSearch() {
searchResults = []
}
// takes list of all mosaics and filters based on search text
func filterAllMosaics(searchText: String) {
searchResults = listOfMosaics.filter { [=10=].contains(searchText) }
}
}
在 AppDelegate 中,我这样称呼它发布通知:
let searchManager = SearchManager()
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
makeRootViewLaunchScreen()
FirebaseApp.configure()
searchManager.getMosaicTitles { (results) in
self.searchManager.listOfMosaics = results
NotificationCenter.default.post(name: NSNotification.Name("mosaicsReturned"), object: nil)
self.stopDisplayingLaunchScreen()
}
// Adds border to bottom of the nav bar
UINavigationBar.appearance().shadowImage = UIImage.imageWithColor(color: UIColor(red:0.00, green:0.87, blue:0.39, alpha:1.0))
// Override point for customization after application launch.
return true
}
func makeRootViewLaunchScreen() {
let mainStoryboard: UIStoryboard = UIStoryboard(name: "LaunchScreen", bundle: nil)
let viewController = mainStoryboard.instantiateViewController(withIdentifier: "launchScreen")
UIApplication.shared.keyWindow?.rootViewController = viewController
}
// reassigns root view after Firebase request complete
func stopDisplayingLaunchScreen() {
let mainStoryboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
let viewController = mainStoryboard.instantiateViewController(withIdentifier: "centralViewController")
UIApplication.shared.keyWindow?.rootViewController = viewController
}
在支持使用检索到的数组填充它的tableView的viewController的viewDidLoad中,我添加了一个Notification Observer。
var listOfMosaics = [String]()
var searchResults = [String]() {
didSet {
tableView.reloadData()
}
}
override func viewDidLoad() {
super.viewDidLoad()
listOfMosaics = searchManager.listOfMosaics
configureSearchBar()
configureSearchBarTextField()
self.tableView.separatorColor = UIColor(red:0.00, green:0.87, blue:0.39, alpha:1.0)
NotificationCenter.default.addObserver(self, selector: #selector(updateListOfMosaics), name: NSNotification.Name("mosaicsReturned"), object: nil)
}
@objc func updateListOfMosaics(notification: Notification) {
listOfMosaics = searchManager.listOfMosaics
}
但是当我调用下面的代码时它不起作用,数组打印为空,因此它不会更新我的 tableView。
extension SearchResultsTableViewController: UISearchBarDelegate {
func searchBarSearchButtonClicked(_ searchBar: UISearchBar) {
searchManager.resetSearch()
searchManager.filterAllMosaics(searchText: searchBar.text!)
tableView.reloadData()
print(listOfMosaics)
print(searchResults)
}
}
在此先感谢您的帮助。
正如@TNguyen 在他的评论中所说,听起来您并没有在等待异步函数 getMosaicTitles()
完成。
您可能希望在调用 运行 时禁用搜索栏按钮,并在调用完成后从完成处理程序中启用它。然后,在结果加载完成之前,用户将无法单击搜索按钮。
您可以在后台线程中从数据库中获取数据并添加一个完成块,以便仅在获取更新的内容后才重新加载 tableView。
这应该对你有用了。我认为您没有将 SearchManager 的实例从您的 AppDelegate 传递给您的 ViewController。我猜你在你的 ViewController 中创建了一个新的 SearchManager 实例,它有一个空数组。
搜索管理员:
class SearchManager {
var searchResults = [String]()
var listOfMosaics = [String]()
func getMosaicTitles(completionHandler: @escaping (_ mosaics: [String]) -> ()) {
Database.database().reference().child("mosaics").observeSingleEvent(of: .value, with: { (snapshot) in
guard let allMosaics = snapshot.value as? [String] else {
print("unable to unwrapp datasnapshot")
completionHandler([]) // <- You should include this too.
return
}
completionHandler(allMosaics)
})
}
func resetSearch() {
searchResults = []
}
func filterAllMosaics(searchText: String) {
searchResults = listOfMosaics.filter { [=10=].contains(searchText) }
}
}
视图控制器:
class TableViewController: UITableViewController {
var searchManager: SearchManager?
var listOfMosaics = [String]()
var searchResults = [String]() {
didSet {
tableView.reloadData()
}
}
override func viewDidLoad() {
super.viewDidLoad()
guard let searchManager = searchManager else { return }
listOfMosaics = searchManager.listOfMosaics
print("List of mosaics: \(listOfMosaics)")
}
override func numberOfSections(in tableView: UITableView) -> Int {
return 0
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 0
}
}
AppDelegate:
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
let searchManager = SearchManager()
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
makeRootViewLaunchScreen()
FirebaseApp.configure()
searchManager.getMosaicTitles { results in
self.searchManager.listOfMosaics = results
self.stopDisplayingLaunchScreen()
}
return true
}
func makeRootViewLaunchScreen() {
let mainStoryboard: UIStoryboard = UIStoryboard(name: "LaunchScreen", bundle: nil)
let viewController = mainStoryboard.instantiateViewController(withIdentifier: "launchScreen")
window?.rootViewController = viewController
window?.makeKeyAndVisible()
}
func stopDisplayingLaunchScreen() {
let mainStoryboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
guard let viewController = mainStoryboard.instantiateViewController(withIdentifier: "centralViewController") as? TableViewController else { return }
let navigationController = UINavigationController(rootViewController: viewController)
viewController.searchManager = searchManager
window?.rootViewController = navigationController
window?.makeKeyAndVisible()
}
}
有人问过与此类似的问题,所以我深表歉意,但其中 none 对我有所帮助。
我正在努力 return 使用完成处理程序从这个异步请求到 Firebase 的值。我从 Firebase 检索的值是一个数组,它确实存在。但是
这是我向 Firebase 发出请求的函数:
class SearchManager {
var searchResults = [String]()
var listOfMosaics = [String]()
// Retrieves company list from Firebase
func getMosaicTitles(completionHandler: @escaping (_ mosaics: [String]) -> ()) {
Database.database().reference().child("mosaics").observeSingleEvent(of: .value, with: { (snapshot) in
guard let allMosaics = snapshot.value as? [String] else {
print("unable to unwrapp datasnapshot")
return
}
completionHandler(allMosaics)
})
}
// resets search results array
func resetSearch() {
searchResults = []
}
// takes list of all mosaics and filters based on search text
func filterAllMosaics(searchText: String) {
searchResults = listOfMosaics.filter { [=10=].contains(searchText) }
}
}
在 AppDelegate 中,我这样称呼它发布通知:
let searchManager = SearchManager()
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
makeRootViewLaunchScreen()
FirebaseApp.configure()
searchManager.getMosaicTitles { (results) in
self.searchManager.listOfMosaics = results
NotificationCenter.default.post(name: NSNotification.Name("mosaicsReturned"), object: nil)
self.stopDisplayingLaunchScreen()
}
// Adds border to bottom of the nav bar
UINavigationBar.appearance().shadowImage = UIImage.imageWithColor(color: UIColor(red:0.00, green:0.87, blue:0.39, alpha:1.0))
// Override point for customization after application launch.
return true
}
func makeRootViewLaunchScreen() {
let mainStoryboard: UIStoryboard = UIStoryboard(name: "LaunchScreen", bundle: nil)
let viewController = mainStoryboard.instantiateViewController(withIdentifier: "launchScreen")
UIApplication.shared.keyWindow?.rootViewController = viewController
}
// reassigns root view after Firebase request complete
func stopDisplayingLaunchScreen() {
let mainStoryboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
let viewController = mainStoryboard.instantiateViewController(withIdentifier: "centralViewController")
UIApplication.shared.keyWindow?.rootViewController = viewController
}
在支持使用检索到的数组填充它的tableView的viewController的viewDidLoad中,我添加了一个Notification Observer。
var listOfMosaics = [String]()
var searchResults = [String]() {
didSet {
tableView.reloadData()
}
}
override func viewDidLoad() {
super.viewDidLoad()
listOfMosaics = searchManager.listOfMosaics
configureSearchBar()
configureSearchBarTextField()
self.tableView.separatorColor = UIColor(red:0.00, green:0.87, blue:0.39, alpha:1.0)
NotificationCenter.default.addObserver(self, selector: #selector(updateListOfMosaics), name: NSNotification.Name("mosaicsReturned"), object: nil)
}
@objc func updateListOfMosaics(notification: Notification) {
listOfMosaics = searchManager.listOfMosaics
}
但是当我调用下面的代码时它不起作用,数组打印为空,因此它不会更新我的 tableView。
extension SearchResultsTableViewController: UISearchBarDelegate {
func searchBarSearchButtonClicked(_ searchBar: UISearchBar) {
searchManager.resetSearch()
searchManager.filterAllMosaics(searchText: searchBar.text!)
tableView.reloadData()
print(listOfMosaics)
print(searchResults)
}
}
在此先感谢您的帮助。
正如@TNguyen 在他的评论中所说,听起来您并没有在等待异步函数 getMosaicTitles()
完成。
您可能希望在调用 运行 时禁用搜索栏按钮,并在调用完成后从完成处理程序中启用它。然后,在结果加载完成之前,用户将无法单击搜索按钮。
您可以在后台线程中从数据库中获取数据并添加一个完成块,以便仅在获取更新的内容后才重新加载 tableView。
这应该对你有用了。我认为您没有将 SearchManager 的实例从您的 AppDelegate 传递给您的 ViewController。我猜你在你的 ViewController 中创建了一个新的 SearchManager 实例,它有一个空数组。
搜索管理员:
class SearchManager {
var searchResults = [String]()
var listOfMosaics = [String]()
func getMosaicTitles(completionHandler: @escaping (_ mosaics: [String]) -> ()) {
Database.database().reference().child("mosaics").observeSingleEvent(of: .value, with: { (snapshot) in
guard let allMosaics = snapshot.value as? [String] else {
print("unable to unwrapp datasnapshot")
completionHandler([]) // <- You should include this too.
return
}
completionHandler(allMosaics)
})
}
func resetSearch() {
searchResults = []
}
func filterAllMosaics(searchText: String) {
searchResults = listOfMosaics.filter { [=10=].contains(searchText) }
}
}
视图控制器:
class TableViewController: UITableViewController {
var searchManager: SearchManager?
var listOfMosaics = [String]()
var searchResults = [String]() {
didSet {
tableView.reloadData()
}
}
override func viewDidLoad() {
super.viewDidLoad()
guard let searchManager = searchManager else { return }
listOfMosaics = searchManager.listOfMosaics
print("List of mosaics: \(listOfMosaics)")
}
override func numberOfSections(in tableView: UITableView) -> Int {
return 0
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 0
}
}
AppDelegate:
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
let searchManager = SearchManager()
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
makeRootViewLaunchScreen()
FirebaseApp.configure()
searchManager.getMosaicTitles { results in
self.searchManager.listOfMosaics = results
self.stopDisplayingLaunchScreen()
}
return true
}
func makeRootViewLaunchScreen() {
let mainStoryboard: UIStoryboard = UIStoryboard(name: "LaunchScreen", bundle: nil)
let viewController = mainStoryboard.instantiateViewController(withIdentifier: "launchScreen")
window?.rootViewController = viewController
window?.makeKeyAndVisible()
}
func stopDisplayingLaunchScreen() {
let mainStoryboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
guard let viewController = mainStoryboard.instantiateViewController(withIdentifier: "centralViewController") as? TableViewController else { return }
let navigationController = UINavigationController(rootViewController: viewController)
viewController.searchManager = searchManager
window?.rootViewController = navigationController
window?.makeKeyAndVisible()
}
}