ios - UIButton不更改图像？

当我单击UIButton saveButton时，我希望saveButton将其图像从saveIcon更改为doneIcon持续1.2秒。我已经这样实现了：

override func viewDidLoad() {
    //create save button
    let saveButton = UIButton(frame: CGRectMake(0, preview.frame.maxY + space, buttonSize, buttonSize))
    saveButton.setBackgroundImage(UIImage(named: "saveIcon"), forState: .Normal)
    saveButton.setBackgroundImage(UIImage(named: "doneIcon"), forState: .Disabled)
    saveButton.center.x = returnButton.center.x
    saveButton.addTarget(self, action: "save:", forControlEvents: .TouchUpInside)
    saveButton.addTarget(self, action: "canSaveAgain:", forControlEvents: .TouchUpInside)
    self.view.addSubview(saveButton)
}

func save(sender: UIButton){
    UIImageWriteToSavedPhotosAlbum(masterpiece, nil, nil, nil)
    sender.enabled = false
    self.performSelector("canSaveAgain:", withObject: sender, afterDelay: 1.2)
}

func canSaveAgain(sender: UIButton){
    sender.enabled = true
}

尽管saveButton已被启用和禁用，但是即使禁用时我将其图像设置为saveButton（即：doneIcon），saveButton.setBackgroundImage(UIImage(named: "doneIcon"), forState: .Disabled)也不会更改其图像。

如果有人能告诉我为什么会这样以及如何临时更改UIButton的图像，我将不胜感激！

最佳答案

我发现了我的问题！实际上，单击UIButton时有两种方法被调用。也就是说，当我按下按钮时，我正在呼叫save:和canSaveAgain:。结果，我立即将按钮同时设置为禁用和启用。

我编辑的代码：

override func viewDidLoad() {
    super.viewDidLoad()

    //create save button
    let saveButton = UIButton(frame: CGRectMake(0, preview.frame.maxY + space, buttonSize, buttonSize))
    saveButton.setImage(UIImage(named: "saveIcon"), forState: .Normal)
    saveButton.setImage(UIImage(named: "doneIcon"), forState: .Disabled)
    saveButton.center.x = returnButton.center.x
    saveButton.addTarget(self, action: "save:", forControlEvents: .TouchUpInside)
    self.view.addSubview(saveButton)
}

func save(sender: UIButton){
    UIImageWriteToSavedPhotosAlbum(masterpiece, nil, nil, nil)
    sender.enabled = false
    self.performSelector("canSaveAgain:", withObject: sender, afterDelay: 1.0)
}

func canSaveAgain(sender: UIButton){
    sender.enabled = true
}