swift：在导航栏中设置按钮图像 [英] swift: setting back button image in nav bar

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)
    }

我试图把它们放到viewWillLoad，但得到同样的错误

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

控制台显示错误消息：

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

我不知道哪个部分出了问题。好像back_img不是零，但我得错误说它是零

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

我已经通过查看示例代码找到了答案。
1）在故事板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）将图像添加到按钮

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：图像应该添加到Images.xcassets文件夹中，参见示例代码， UICatalog ，了解详情。

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

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