打开应用程序时自动更新UI

Question

我已经成功地让我的天气应用程序工作了，显示了当前的测试数据等等。但现在唯一的问题是，我只能通过按下我的“刷新”按钮来获取数据。如何使我的应用程序在打开UI时更新它？

这是我的工作代码：

import Foundation
import UIKit




class ViewController: UIViewController {
@IBOutlet weak var tempLabel: UILabel!
@IBOutlet weak var humidLabel: UILabel!
@IBOutlet weak var refresh: UIButton!
@IBOutlet weak var negitiveSymbol: UILabel!


func getTemp(){
    var urlString = "http://torsher.ca/Weather/temperature.txt"
    var url = NSURL(string: urlString)
    let task = NSURLSession.sharedSession().dataTaskWithRequest(NSURLRequest(URL: url!, cachePolicy: NSURLRequestCachePolicy.ReloadIgnoringLocalAndRemoteCacheData, timeoutInterval: 15.0)){(data, response, error) in
        var urlContent = (NSString(data: data, encoding: NSUTF8StringEncoding))
        var tempContent:String = urlContent as String
        println(tempContent)

        dispatch_async(dispatch_get_main_queue()) {
            self.tempLabel.text = (tempContent)

        }
    }

    task.resume()
}

func getHumid(){
    var urlString = "http://torsher.ca/Weather/humidity.txt"
    var url = NSURL(string: urlString)
    let task = NSURLSession.sharedSession().dataTaskWithRequest(NSURLRequest(URL: url!, cachePolicy: NSURLRequestCachePolicy.ReloadIgnoringLocalAndRemoteCacheData, timeoutInterval: 15.0)){(data, response, error) in
        var urlContent = (NSString(data: data, encoding: NSUTF8StringEncoding))
        var humidContent:String = urlContent as String
        println(humidContent)

        dispatch_async(dispatch_get_main_queue()) {
            self.humidLabel.text = (humidContent)
        }
    }

    task.resume()
}


@IBAction func refreshPressed(sender: AnyObject, forEvent event: UIEvent) {
    getTemp()

}
@IBAction func refreshPress(sender: AnyObject, forEvent event: UIEvent) {
     getHumid()
}



        override func viewDidLoad() {
        super.viewDidLoad()

}
    }

我所看到的是使用AppDelegate.swift文件及其内置的func "func applicationDidEnterBackground(application: UIApplication)“，但是我尝试的每一件事要么破坏了应用程序，要么就是不能工作。我想让应用程序运行getTemp函数，getHumid函数，然后用值更新UI，就像在按钮中的IBAction函数中所做的那样。

任何帮助都是非常感谢的。

编辑：

  //
 //  ViewController.swift
 //  WeatherStation
 //
 //  Created by on 2015-04-16.
 //  Copyright (c) 2015 . All rights reserved.
 //

 import Foundation
 import UIKit




 class ViewController: UIViewController {
 @IBOutlet weak var tempLabel: UILabel!
 @IBOutlet weak var humidLabel: UILabel!
 @IBOutlet weak var refresh: UIButton!
 @IBOutlet weak var negitiveSymbol: UILabel!
 @IBOutlet weak var dateUpdate: UILabel!


func getTemp() //Gets the temeprature from the server and displays it.
{
    var urlString = "http://torsher.ca/Weather/temperature.txt"
    var url = NSURL(string: urlString)
    let task = NSURLSession.sharedSession().dataTaskWithRequest(NSURLRequest(URL: url!, cachePolicy: NSURLRequestCachePolicy.ReloadIgnoringLocalAndRemoteCacheData, timeoutInterval: 15.0)){(data, response, error) in
        var urlContent = (NSString(data: data, encoding: NSUTF8StringEncoding))
        var tempContent:String = urlContent as String
        println(tempContent)

        dispatch_async(dispatch_get_main_queue()) {
            self.tempLabel.text = (tempContent)

        }
    }

    task.resume()
}

func getHumid() //Gets the humidity from the server and displays it.
{
    var urlString = "http://torsher.ca/Weather/humidity.txt"
    var url = NSURL(string: urlString)
    let task = NSURLSession.sharedSession().dataTaskWithRequest(NSURLRequest(URL: url!, cachePolicy: NSURLRequestCachePolicy.ReloadIgnoringLocalAndRemoteCacheData, timeoutInterval: 15.0)){(data, response, error) in
        var urlContent = (NSString(data: data, encoding: NSUTF8StringEncoding))
        var humidContent:String = urlContent as String
        println(humidContent)

        dispatch_async(dispatch_get_main_queue()) {
            self.humidLabel.text = (humidContent)
        }
    }

    task.resume() 
}


@IBAction func refreshPressed(sender: AnyObject, forEvent event: UIEvent) //Updates UI with current temperature when refresh is pressed.
{
    getTemp()
}

@IBAction func refreshPress(sender: AnyObject, forEvent event: UIEvent) //Updates UI with current humidity when refresh is pressed.
{
     getHumid()
}

func appWasOpened(notification: NSNotification!)
{
    getHumid()
    getTemp()
}

deinit {
    NSNotificationCenter.defaultCenter().removeObserver(foregroundNotification)
}


override func viewDidLoad()
{
super.viewDidLoad()
NSNotificationCenter.defaultCenter().addObserver(self, selector:        
"appWasOpened:", name: UIApplicationWillEnterForegroundNotification, object:         
nil)
    }
}

试图添加第二个解决方案时，无法使用deinit()运行。

Answer 1

让应用程序每次打开时做一些事情的标准技巧是，在应用程序第一次打开时将日期存储在NSUserDefaults中，然后根据应用程序再次打开时的当前日期检查存储的日期。如果时间已经过了足够多的时间，你就会做这个动作，否则你就不会做了。如果你做了这个动作，那么你可以将当前的日期存储回NSUserDefaults中，开始一个新的句号。

Answer 2

第一个解决方案:您可以在viewcontroller中使用通知，将其添加到viewDidLoad中

NSNotificationCenter.defaultCenter().addObserverForName(UIApplicationWillEnterForegroundNotification, object: nil, queue: NSOperationQueue.mainQueue()) 
{ [unowned self] notification in

    getHumid()
    getTemp()

}

第二种解决方案:在viewDidLoad中交替使用

    NSNotificationCenter.defaultCenter().addObserver(self, selector: "appWasOpened:", name: UIApplicationWillEnterForegroundNotification, object: nil)

和viewController的一个新函数

func appWasOpened(notification: NSNotification!) 
{
    getHumid()
    getTemp()
}

在这两种情况下，()都需要覆盖denit (这将防止在取消分配视图控制器时调用观察)。

deinit {
   NSNotificationCenter.defaultCenter().removeObserver(self)
}