extension may not contain stored properties and no member problems in swift

Question

I am not able to understand why I am getting these errors. someone please help me. Here is the source code

import UIKit
import AVFoundation

// MARK: - PlaySoundsViewController: AVAudioPlayerDelegate

extension PlaySoundsViewController: AVAudioPlayerDelegate {

    var audioEngine = AVAudioEngine()


    // MARK: Alerts

    struct Alerts {
    static let DismissAlert = "Dismiss"
    static let RecordingDisabledTitle = "Recording disabled"
    static let RecordginDisabledMessage = "Youve disabled this app from recording your microphone. Check settings"
    static let RecodingFailedTitle = "Recording failed"
    static let RecordingFailedMessage = "Something went wrong with the recording"
    static let AudioRecordedError = "Audio Recorder Error"
    static let AudioSessionError = "Audio Session Error"
    static let AudioRecordingError = "Audio Recording Error"
    static let AudioFileError = "Audio File Error"
    static let AudioEngineError = "Audio Engine Error"
    }

    // MARK: PlayingState (raw values correspond to sender tags)

    enum PlayingState { case playing, notPlaying }

    // MARK: Audio Functions

    func setupAudio() {
        // initialize (recording) audio file
        do {
            audioFile = try AVAudioFile(forReading: recordedAudioURL as URL)
        } catch {
            showAlert(Alerts.AudioFileError, message: String(describing: error))
        }        
    }

    func playSound(rate: Float? = nil, pitch: Float? = nil, echo: Bool = false, reverb: Bool = false) {

        // initialize audio engine components
        audioEngine = AVAudioEngine()

        // node for playing audio
        audioPlayerNode = AVAudioPlayerNode()
        audioEngine.attach(audioPlayerNode)

        // node for adjusting rate/pitch
        let changeRatePitchNode = AVAudioUnitTimePitch()
        if let pitch = pitch {
            changeRatePitchNode.pitch = pitch
        }
        if let rate = rate {
            changeRatePitchNode.rate = rate
        }
        audioEngine.attach(changeRatePitchNode)

        // node for echo
        let echoNode = AVAudioUnitDistortion()
        echoNode.loadFactoryPreset(.multiEcho1)
        audioEngine.attach(echoNode)

        // node for reverb
        let reverbNode = AVAudioUnitReverb()
        reverbNode.loadFactoryPreset(.cathedral)
        reverbNode.wetDryMix = 50
        audioEngine.attach(reverbNode)

        // connect nodes
        if echo == true && reverb == true {
            connectAudioNodes(audioPlayerNode, changeRatePitchNode, echoNode, reverbNode, audioEngine.outputNode)
        } else if echo == true {
            connectAudioNodes(audioPlayerNode, changeRatePitchNode, echoNode, audioEngine.outputNode)
        } else if reverb == true {
            connectAudioNodes(audioPlayerNode, changeRatePitchNode, reverbNode, audioEngine.outputNode)
        } else {
            connectAudioNodes(audioPlayerNode, changeRatePitchNode, audioEngine.outputNode)
        }

        // schedule to play and start the engine!
        audioPlayerNode.stop()
        audioPlayerNode.scheduleFile(audioFile, at: nil) {

            var delayInSeconds: Double = 0

            if let lastRenderTime = self.audioPlayerNode.lastRenderTime, let playerTime = self.audioPlayerNode.playerTime(forNodeTime: lastRenderTime) {

                if let rate = rate {
                    delayInSeconds = Double(self.audioFile.length - playerTime.sampleTime) / Double(self.audioFile.processingFormat.sampleRate) / Double(rate)
                } else {
                    delayInSeconds = Double(self.audioFile.length - playerTime.sampleTime) / Double(self.audioFile.processingFormat.sampleRate)
                }
            }

            // schedule a stop timer for when audio finishes playing
            self.stopTimer = Timer(timeInterval: delayInSeconds, target: self, selector: #selector(PlaySoundsViewController.stopAudio), userInfo: nil, repeats: false)
            RunLoop.main.add(self.stopTimer!, forMode: RunLoopMode.defaultRunLoopMode)
        }

        do {
            try audioEngine.start()
        } catch {
            showAlert(Alerts.AudioEngineError, message: String(describing: error))
            return
        }

        // play the recording!
        audioPlayerNode.play()
    }

    func stopAudio() {

        if let audioPlayerNode = audioPlayerNode {
            audioPlayerNode.stop()
        }

        if let stopTimer = stopTimer {
            stopTimer.invalidate()
        }

        configureUI(.notPlaying)

        if let audioEngine = audioEngine {
            audioEngine.stop()
            audioEngine.reset()
        }
    }

    // MARK: Connect List of Audio Nodes

    func connectAudioNodes(_ nodes: AVAudioNode...) {
        for x in 0..<nodes.count-1 {
            audioEngine.connect(nodes[x], to: nodes[x+1], format: audioFile.processingFormat)
        }
    }

    // MARK: UI Functions

    func configureUI(_ playState: PlayingState) {
        switch(playState) {
        case .playing:
            setPlayButtonsEnabled(false)
            stopButton.isEnabled = true
        case .notPlaying:
            setPlayButtonsEnabled(true)
            stopButton.isEnabled = false
        }
    }

    func setPlayButtonsEnabled(_ enabled: Bool) {
        snailButton.isEnabled = enabled
        chipmunkButton.isEnabled = enabled
        rabbitButton.isEnabled = enabled
        vaderButton.isEnabled = enabled
        echoButton.isEnabled = enabled
        reverbButton.isEnabled = enabled
    }

    func showAlert(_ title: String, message: String) {
        let alert = UIAlertController(title: title, message: message, preferredStyle: .alert)
        alert.addAction(UIAlertAction(title: Alerts.DismissAlert, style: .default, handler: nil))
        self.present(alert, animated: true, completion: nil)
    }
}

The screenshot of the error is in the link below.

Screenshot !

Answer 1

You can not declare var audioEngine = AVAudioEngine() inside an extension. Declare it inside PlaySoundsViewController class instead.

Extensions are meant to augment behaviours, not fundamentally change a class.

@source: Why can't you add stored properties to extensions?