无法将NSMutableArray类型的值分配给UIBarButtonItem类型

Question

I am developing an iOS audio app as a learning project. I'm having a problem in one of the functions, which checks if the player is playing or paused/stopped. If it's playing it should change the button in the button bar to a "pause" button, or if it's paused or stopped, change the button to a "play" button. I am assigning the button bar items to a variable "items" as a NSMutableArray, then make the necessary change to the button, then assign "items" back to the button bar items to update the display.

In my code I am getting an error on the line:

self.toolbar.items = items

The error message is

Cannot assign value of type NSMutableArray to Type UIBarButtonItem

I assume that I need to cast the NSMutableArray, I've tried using Array, and when I do the error goes away but the buttons break.

The related parts of my code are:

@IBOutlet weak var toolbar: UIToolbar!

@IBOutlet var playButton: UIBarButtonItem!


@IBAction func playPausePressed(sender: AnyObject) {
    let playbackState = self.player.playbackState as MPMusicPlaybackState
    let items = NSMutableArray(array: self.toolbar.items!)
    if playbackState == .Stopped || playbackState == .Paused{
        self.player.play()
        items[2] = self.pauseButton
    } else if playbackState == .Playing{
        self.player.pause()
        items[2] = self.playButton
    }
    self.toolbar.items = items
}

Any help or direction would be much appreciated. Thanks!

Answer 1

The error occurs because NSMutableArray is not related to Swift Array

Why not using the native property directly? Due to reference semantics it's not necessary to create a temporary array.

@IBAction func playPausePressed(sender: AnyObject) {
    let playbackState = self.player.playbackState as MPMusicPlaybackState
    var items = self.toolbar.items!
    if playbackState == .Stopped || playbackState == .Paused{
        self.player.play()
        items[2] = self.pauseButton
    } else if playbackState == .Playing{
        self.player.pause()
        items[2] = self.playButton
    }
}

Answer 2

I have a feeling that you could do better. Do you really need to switch between two different buttons for your items[2] ?

UIBarButtonItem can be used pretty much like a regular UIButton with different states. I'm assuming you'd want to switch between a play and pause image whenever your player is paused/playing. You could do this by setting two different images to your UIBarButtonItem ( setBackgroundImage(_:forState:barMetrics:) ) then by setting the appropriate state when your playbackState changes.