ios – UIBarButtonItem更改播放/暂停按钮的图像

一切正常,但按钮不会改变.我也尝试使用.image属性而不是.setBackGroundImage方法,但是按钮在单击时变为空白.

这是代码

import UIKit
import AVFoundation

class ViewController: UIViewController {

var audioPlayer = AVAudioPlayer()

var pauseImage:UIImage?
var playImage:UIImage?

@IBOutlet weak var btnPlayPause: UIBarButtonItem!

@IBOutlet weak var sldVolume: UiSlider!

@IBAction func sldVolumeChanged(sender: AnyObject) {

    audioPlayer.volume = sldVolume.value

}

@IBAction func actpressedPlayPause(sender: AnyObject) {

    if audioPlayer.playing {
        audioPlayer.pause()
        btnPlayPause.setBackgroundImage(playImage,forState: .normal,barMetrics: .Default)

    } else {
        audioPlayer.play()
        btnPlayPause.setBackgroundImage(pauseImage,barMetrics: .Default)
    }

}

@IBAction func actStoppressed(sender: AnyObject) {

    audioPlayer.stop()
    audioPlayer.currentTime = 0

}

override func viewDidLoad() {
    super.viewDidLoad()

    var pauseImagePath = NSBundle.mainBundle().pathForResource("pause",ofType: "png")
    pauseImagePath = pauseImagePath!.stringByAddingPercentEscapesUsingEncoding(NSUTF8StringEncoding)
    pauseImage = UIImage(contentsOfFile: pauseImagePath!)

    var playImagePath = NSBundle.mainBundle().pathForResource("play",ofType: "png")
    playImagePath = playImagePath!.stringByAddingPercentEscapesUsingEncoding(NSUTF8StringEncoding)
    playImage = UIImage(contentsOfFile: pauseImagePath!)



    var audioPath = NSBundle.mainBundle().pathForResource("minuetcminor",ofType: "mp3")

    audioPath = audioPath!.stringByAddingPercentEscapesUsingEncoding(NSUTF8StringEncoding)

    var error : NSError? = nil

    audioPlayer = AVAudioPlayer(contentsOfURL: NSURL(string: audioPath!),error: &error)

}

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


}