在swift中从另一个ViewController调用函数 [英] Calling function from another ViewController in swift

问题描述

我已经查看过Stackoverflow但我无法得到答案。我想创建停止在另一个ViewController中播放声音的函数。但是当我点击停止按钮时，它会破解并显示EXC_BAD_INSTRUCTION（code = EXC_I386_INVOP，subcode = 0x0）。这是我的代码。

I have already looked in Stackoverflow but I can't get an answer. I want to create function that stop playing the sound in another ViewController. But when I clicked the stop button, it cracked and showed "EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)". This is my code.

First ViewController

First ViewController

import UIKit
import AVFoundation

class FirstVC: UIViewController {

   var metronome: AVAudioPlayer!
   override func viewDidLoad() {
       super.viewDidLoad()
   do {
        let resourcePath1 = Bundle.main.path(forResource: "music", ofType: "mp3")
        let url = NSURL(fileURLWithPath: resourcePath1!)
        try metronome = AVAudioPlayer(contentsOf: url as URL)

        metronome.prepareToPlay()
        metronome.play()
    } catch let err as NSError {
        print(err.debugDescription)
    }
}

和另一个Viewcontroller是

and another Viewcontroller is

import UIKit
class SecondVC: UIViewController {
   var metronomePlay = FirstVC()

@IBAction func stopBtnPressed(_ sender: Any) {
   metronomePlay.metronome.stop() //"EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)"
   }
}

推荐答案

您正在创建FirstVC的新副本，并在尚未初始化的内容上调用stop。

You are creating a NEW copy of FirstVC and calling stop on something that is not yet initialised.

在这种情况下你真的应该使用委托，比如

You should really use a delegate in this case, something like

protocol controlsAudio {
   func startAudio()
   func stopAudio()
}

class FirstVC: UIViewController, controlsAudio {
    func startAudio() {}
    func stopAudio() {}

    // later in the code when you present SecondVC
    func displaySecondVC() {
       let vc = SecondVC()
       vc.delegate = self
       self.present(vc, animated: true)
    }

}

class SecondVC: UIViewController {
    var delegate: controlsAudio?

    // to start audio call self.delegate?.startAudio)
    // to stop audio call self.delegate?.stopAudio)

}

所以你将第一个VC传递给第二个VC，所以当你调用这些函数时，你正在实际执行它正在使用的FirstVC，而不是创建一个新的。

So you are passing first VC to the second VC, so when you call these functions you are doing it on the actual FirstVC that is in use, rather than creating a new one.

如果您愿意，可以通过用<$ c $替换 var delegate：controlsAudio？来执行此操作c> var firstVC：FirstVC？并指定它，但我不推荐它

You could do this without protocols if you like by replacing the var delegate: controlsAudio? with var firstVC: FirstVC? and assigning that, but I wouldn't recommend it

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