Expression resolves to an unused function

Question

First of all let me say that I am very new to programming. What I'm trying to do is add a button that when pressed plays music, and when pressed again the music stops. Ideally when the button is pressed for a third time the music will have reset. Whilst trying to achieve this I'm getting the error message "Expression resolves to an unused function", as I am very new all the help I find online doesn't make any sense to me.

import UIKit
import AVFoundation

class ViewController: UIViewController {
    @IBOutlet weak var janitor: UIImageView!
    var pianoSound = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("C", ofType: "m4a")!)
    var audioPlayer = AVAudioPlayer()

    override func viewDidLoad() {
        super.viewDidLoad()

        audioPlayer = AVAudioPlayer(contentsOfURL: pianoSound, error: nil)
        audioPlayer.prepareToPlay()
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }


        @IBAction func PianoC(sender: AnyObject) {

        audioPlayer.play()

            if audioPlayer.playing { audioPlayer.stop} else {  audioPlayer.play}
}
}

`stop` --> `stop()`, `play` --> `play()` ... – Martin R Apr 09 '15 at 21:05 — Martin R, Apr 09 '15 at 21:05

score 29 · Accepted Answer · answered Apr 10 '15 at 01:40

Swooping in here after Martin R's comment ...

if audioPlayer.playing { audioPlayer.stop} else {  audioPlayer.play}

On this line, you are not calling the stop and play functions, but simply accessing them. Resolving to an unused function is trying to tell you that you have an expression that is returning a function type, but you are never calling it (audioPlayer.stop and audioPlayer.play are the expressions in question here).

To rid yourself of this error, and probably produce the correct behavior, try calling the functions.

if audioPlayer.playing { 
    audioPlayer.stop()
} else {  
    audioPlayer.play()
}

score 10 · Answer 2 · answered Apr 06 '18 at 09:08

Swift 4: Just add the braces '()' next to the method name

override func viewWillAppear(_ animated: Bool) {
   addView //error: Expression resolves to an unused function
}

func addView(){
}

Solution:

override func viewWillAppear(_ animated: Bool) {
   addView()
}

score 5 · Answer 3 · answered Oct 16 '15 at 13:22

5

Here's a simplified version of Brian's answer:

audioPlayer.playing
    ? audioPlayer.stop()
    : audioPlayer.play()

answered Oct 16 '15 at 13:22

Rudolf Adamkovič

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@Fr4nc3sc0NL Why's that? – Rudolf Adamkovič Feb 17 '16 at 11:13
1

@RudolfAdamkovic You don't explain what this code is doing – grooveplex May 05 '16 at 20:02
1

@grooveplex It's a ternary expression. If the audio player is playing, it will be stopped. If not, it will start playing. – Rudolf Adamkovič May 05 '16 at 20:04
2

Its basically shorthand of if else condition. The code translates to - `If audioPlayer.playing audioPlayer.stop() else audioPlayer.play()` – Yash Tamakuwala Jun 30 '16 at 11:05

score 0 · Answer 4 · answered Sep 20 '16 at 16:25

if audioPlayer.playing { audioPlayer.stop} else { audioPlayer.play} is just accessing the member variables. It's not doing anything.

I am sure you're intention was to do audioPlayer.stop() and audioPlayer.start().

However just to explain the ERROR and not to solve your issue: had you done something like

if audioPlayer.playing { self.playerStatus= audioPlayer.stop} else {  self.playerStatus = audioPlayer.play}

Then you were actually doing something you were setting a parameter. accessing or just getting a parameter is stupid in the eyes of the compiler :)

Expression resolves to an unused function

4 Answers4

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