Swift-如何在按钮上显示图像？

override func viewDidLoad()
{
    super.viewDidLoad()

    var birdTexture1 = UIImage(named: "fish.png") as UIImage
    button1.frame = CGRectMake(100,10,50,150)
    button1.setimage(birdTexture1,forState: .normal)

    button1.setTitle("Testing",forState: UIControlState.normal)
    button1.addTarget(self,action: "btnAction:",forControlEvents:  UIControlEvents.TouchUpInside)
    self.view.addSubview(button1)

    // Do any additional setup after loading the view,typically from a nib.
}

通过上面的代码,我得到了以下输出

但实际图像是这样的 –