使用闭包中的委托传递数据

Question

我有两个视图控制器，我正在尝试将数据从一个传递到另一个。 数据从 MKLocalSearch 闭包返回。 但我似乎无法运行我的委托方法。 我希望有人能对此有所了解？ 我模拟了我正在尝试做的事情的较小版本。另外，我不使用故事板。 我编写了所有代码。这是代码...

import UIKit
import MapKit
protocol SendDataDelegate {
func sendData(data: String)
}
class OneViewController: UIViewController {
var delegate: SendDataDelegate?
override func viewDidLoad() {
super.viewDidLoad()
doSearch() { coord in
if let coord = coord {
//When the execution gets here, coord does have
//the values to be sent to the nexr view controller.
self.delegate?.sendData(data: "(coord)")
let twoViewController = TwoViewController()
self.present(twoViewController, animated: true)
}
}
}
func doSearch(completion: @escaping (CLLocationCoordinate2D?) -> Void) {
var coord: CLLocationCoordinate2D?
let request = MKLocalSearchRequest()
request.naturalLanguageQuery = "New York"
let search = MKLocalSearch(request: request)
search.start(completionHandler: {(response, error) in
if error != nil {
print("Error occured in search:(error!.localizedDescription)")
} else if response!.mapItems.count == 0 {
print("No matches found")
} else {
print("Matches found")
coord = response?.mapItems[0].placemark.coordinate
}
completion(coord)
})
}
}
import UIKit
class TwoViewController: UIViewController, SendDataDelegate {
var myData: String = ""
var oneViewController = OneViewController()
override func viewDidLoad() {
super.viewDidLoad()
oneViewController.delegate = self
}
func sendData(data: String) {
myData = data
print ("myData: (myData)")
}
}

Answer 1

在你的TwoViewController中，你有一个属性保存另一个OneViewController实例，并将其委托设置为self。

因此，每次创建TwoViewController的实例时，都会创建一个新的OneViewController实例，但由于显示OneViewController的实际视图，它们实际上都不是那个实例。

在您的情况下，委托模式不合适，您最好直接调用TwoViewController的方法：

class OneViewController: UIViewController {
//no need to have a delegate
override func viewDidLoad() {
super.viewDidLoad()
doSearch() { coord in
if let coord = coord {
//When the execution gets here, coord does have
//the values to be sent to the nexr view controller.
let twoViewController = TwoViewController()
twoViewController.sendData(data: "(coord)")
self.present(twoViewController, animated: true)
}
}
}
//...    
}
class TwoViewController: UIViewController {
var myData: String = ""
//Creating a new instance of `OneViewController` has no meaning.
override func viewDidLoad() {
super.viewDidLoad()
//Useless to set the delegate of newly created `OneViewController`.
}
func sendData(data: String) {
myData = data
print ("myData: (myData)")
}
}

如果您有任何理由在TwoViewController拥有房产oneViewController，请解释原因。您当前的代码无法解释任何内容。