使用NotificationCenter Observer处理异步请求 [英] Using NotificationCenter Observer to Handle Asynchronous Requests
问题描述
类似的问题已经被问到了,所以我很抱歉,但没有人能够帮助我。
我努力从这个异步向Firebase请求完成处理程序。我从Firebase中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]()
从Firebase获取公司列表
func getMosaicTitles(completionHandler:@escaping(_ mosaics:[String]) - >()){
Database.database()。reference()。child(mosaics)。observeSingleEvent(.value ,其中:{(snapshot)in
guard let allMosaics = snapshot.value as?[String] else {
print(无法解开datasnapshot)
return
}
completionHandler(allMosaics)
})
}
//重置搜索结果数组
func resetSearch(){
searchResults = []
}
//根据搜索文本获取所有马赛克和过滤器列表
func filterAllMosaics(searchText:String){
sea rchResults = listOfMosaics.filter {$ 0.contains(searchText)}
}
}
在AppDelegate中,我把它称为发布通知:
$ b $ pre $ let searchManager = SearchManager()
func应用程序(_ application:UIApplication,didFinishLaunchingWithOptions launchOptions:[UIApplicationLaunchOptionsKey:Any]?) - > Bool {
makeRootViewLaunchScreen()
FirebaseApp.configure()
searchManager.getMosaicTitles {$ results $ b $ self.searchManager.listOfMosaics = results
NotificationCenter .default.post(name:NSNotification.Name(mosaicsReturned),object:nil)
self.stopDisplayingLaunchScreen()
}
//将边框添加到导航栏底部
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
$ b func makeRootViewLaunchScreen(){
let mainStoryboard:UIStoryboard = UIStoryboard(name:LaunchScreen,bundle:nil)
let viewController = mainStoryboard.instantiateViewController(withIdentifier:launchScreen)
UIApplication.shared.keyWindow?.rootViewController = viewController
}
//在Firebase请求完成后重新分配根视图
func stopDisplayingLaunchScreen(){
let mainStoryboard:UIStoryboard = UIStoryboard(name:Main,bundle:nil)
let viewController = mainStoryboard.instantiateViewController(withIdentifier:centralViewController)
UIApplication .shared.keyWindow?.rootViewController = viewController
}
在viewController的viewDidLoad支持tableView,它使用检索的数组来填充它,我添加一个通知观察者。
var listOfMosaics = [String]()
var searchResul ts = [String](){
didSet {
tableView.reloadData()
}
}
覆盖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它不工作数组打印为空,因此它不会更新我的tableView。
扩展程序SearchResultsTableViewController:UISearchBarDelegate {
func searchBarSearchButtonClicked(_ searchBar:UISearchBar){
searchManager.resetSearch()
searchManager.filterAllMosaics(searchText:searchBar.text!)
tableView.reloadData()
print(listOfMosaics)$ b $ print(searchResults)
$ p 感谢您的帮忙。
解决方案现在,我想你没有把你的AppDelegate的SearchManager实例传递给你的ViewController。我猜你在ViewController中创建了一个新的SearchManager实例,它有一个空的数组。
搜索管理器
pre $ $ $ $ $ $ $ $ $ $ $ $ $ )
func getMosaicTitles(completionHandler:@escaping(_ mosaics:[String]) - >()){
Database.database()。reference()。child(mosaics ).observeSingleEvent(:.value,其中:{(snapshot)in
guard let allMosaics = snapshot.value as?[String] else {
print(无法解开datasnapshot)
completionHandler([])//< - 你也应该包括这个。
return
}
completionHandler(allMosaics)
})
}
func resetSearch(){
searchResults = []
}
func filterAllMosaics(searchText:String){
se archResults = listOfMosaics.filter {$ 0.contains(searchText)}
}
}
视图控制器:
class TableViewController:UITableViewController {
var searchManager:SearchManager?
var listOfMosaics = [String]()
var searchResults = [String](){
didSet {
tableView.reloadData()
}
}
$ b $重写func viewDidLoad(){
super.viewDidLoad()
guard让searchManager = searchManager else {return}
listOfMosaics = searchManager.listOfMosaics
print (马赛克列表:\(listOfMosaics))
}
覆盖func numberOfSections(在tableView:UITableView中) - > Int {
return 0
}
覆盖func tableView(_ tableView:UITableView,numberOfRowsInSection section:Int) - > Int {
return 0
}
}
AppDelegate:
class AppDelegate:UIResponder,UIApplicationDelegate {
var window:UIWindow?
让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
$ b func makeRootViewLaunchScreen(){
let mainStoryboard:UIStoryboard = UIStoryboard(name:LaunchScreen,bundle:nil)
让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()
}
}
Similar questions to this have been asked so I apologize, but none of them have been able to help me.
I am struggling to return the value from this asynchronous request to Firebase with a completion handler. The value I am retrieving from Firebase is an array and it does exist. But
Here is my function for making the request to Firebase:
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 { $0.contains(searchText) }
}
}
And in the AppDelegate I call it like this posting a Notification:
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
}
In the viewDidLoad of the viewController that supports the tableView that uses the retrieved array to populate it I add a 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
}
But when I call the below code it doesn't work the arrays print as empty and as a result it doesn't update my tableView.
extension SearchResultsTableViewController: UISearchBarDelegate {
func searchBarSearchButtonClicked(_ searchBar: UISearchBar) {
searchManager.resetSearch()
searchManager.filterAllMosaics(searchText: searchBar.text!)
tableView.reloadData()
print(listOfMosaics)
print(searchResults)
}
}
Thank you in advanced for the help.
This should work for you now. I think you didn't pass the instance of SearchManager from your AppDelegate to your ViewController. I'm guessing you created a new instance of SearchManager in your ViewController, which has an empty array.
Search Manager:
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 { $0.contains(searchText) }
}
}
View Controller:
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()
}
}
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