swift - 仅在变量输出发生变化时触发事件

Question

我创建了以下抛硬币程序，该程序每秒每次抛硬币都会触发一个音频文件。我想知道如何更改此设置，以便仅当结果从正面变为反面时才触发音频，反之亦然。不是像现在这样每一秒。非常感谢任何帮助。

import UIKit
import AVFoundation

class ViewController: UIViewController {

var times: Timer!
var timer: Timer!
var coinFlip : Int = 0
var coinResult : String = ""
var audioPlayer : AVAudioPlayer!
let soundArray = ["note1", "note7"]

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
    times = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(fiftyFifty), userInfo: nil, repeats: true)
    timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(result), userInfo: nil, repeats: true)
    result()

}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

func fiftyFifty() -> Int {

    coinFlip = Int(arc4random_uniform(2))

    return coinFlip
}
func result() -> String {

    if coinFlip == 1 {
        coinResult = "Heads"
print("Heads")
        playSound(soundFileName: soundArray[0])
    }
    else {
        coinResult = "Tails"
print("Tails")
        playSound(soundFileName: soundArray[1])
    }
}

func playSound(soundFileName : String) {
    let soundURL = Bundle.main.url(forResource: soundFileName, withExtension: "wav")
    do {
        audioPlayer = try AVAudioPlayer(contentsOf: soundURL!)
    }
    catch  {
        print(error)
    }
    audioPlayer.play()
}
}

我现在对其进行了更改，添加了 result() 的新变量输出 coinResult。不确定这是否有帮助，但希望有帮助。

Answer 1

如果我理解得很好，当硬币翻转时，你想播放一首歌曲，在这种情况下，你可以简单地将 coinFlip 声明更改为:

var coinFlip : Int = 0 {
    didSet {
        result()
    }
}

didSet 是一个属性观察器，用于观察并响应属性值的变化。

didSet is called immediately after the new value is stored.

您可以在Apple's documentation中阅读有关属性观察者的更多信息。 .

<小时/>

编辑:您的代码将如下所示:

import UIKit
import AVFoundation

class ViewController: UIViewController {

var times: Timer!
var timer: Timer!

// Change this
var coinFlip : Int = 0 {
    didSet {
        result()
    }
}

var audioPlayer : AVAudioPlayer!
let soundArray = ["note1", "note7"]

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
    times = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(fiftyFifty), userInfo: nil, repeats: true)
    timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(result), userInfo: nil, repeats: true)
    result()

}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

func fiftyFifty() -> Int {

    coinFlip = Int(arc4random_uniform(2))

    return coinFlip
}
func result() {

    if coinFlip == 1 {
print("Heads")
        playSound(soundFileName: soundArray[0])
    }
    else {
print("Tails")
        playSound(soundFileName: soundArray[1])
    }
}

func playSound(soundFileName : String) {
    let soundURL = Bundle.main.url(forResource: soundFileName, withExtension: "wav")
    do {
        audioPlayer = try AVAudioPlayer(contentsOf: soundURL!)
    }
    catch  {
        print(error)
    }
    audioPlayer.play()
}
}