swift:在导航栏中设置后退按钮图像

问题描述

我正在尝试在控制器的导航栏中设置后退按钮图像，这是我在 viewDidLoad() 中的代码:

I'm trying to set the back button image in nav bar in my controller, here's my code in viewDidLoad():

        var backImg: UIImage? = UIImage(named: "back_btn.png")
    println(backImg)
    if var back_img = backImg  {
        println("GET IT")
        println(back_img)
        println(UIControlState.Normal)
        println(UIBarMetrics.Default)
    self.navigationController.navigationBar.backItem.backBarButtonItem.setBackButtonBackgroundImage(back_img, forState: UIControlState.Normal, barMetrics: UIBarMetrics.Default)
    }

我试图将它们放到 viewWillLoad 中，但得到了同样的错误

I tried to put them to viewWillLoad, but getting the same error

带有错误消息的控制台:

Console with error message:

<UIImage: 0x7ff37bd85750>
GET IT
<UIImage: 0x7ff37bd85750>
VSC14UIControlState (has 1 child)
(Enum Value)
fatal error: unexpectedly found nil while unwrapping an Optional value

我不知道哪一部分出了问题.似乎 back_img 不是 nil，但我收到错误说它是 nil

I don't know which part went wrong. Seems like the back_img is not nil, but I got error saying it's nil

谢谢！

推荐答案

我通过查看示例代码找到了答案.1)在情节提要中创建一个条形按钮项.2) 使用 IBOutlet 将该按钮链接到控制器3) 给按钮添加图片

I have figured out by looking into sample code. 1) Create a bar button item in storyboard. 2) Link that button to controller using IBOutlet 3) Add image to the button

 var backImg: UIImage = UIImage(named: "back_btn")
 backBtn.setBackgroundImage(backImg, forState: .Normal, barMetrics: .Default)

PS:图片应添加到 Images.xcassets 文件夹，请参阅示例代码，UICatalog，了解详情.

PS: image should be added to Images.xcassets folder, see sample code, UICatalog , for details.

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