来自'UIImage'的沮丧？ 'UIImage'只展开选项 [英] Downcast from 'UIImage?' to 'UIImage' only unwraps optionals

问题描述

我正在用图片创建一个 UIButton ，

I'm creating a UIButton with an image,

我为此编写了以下代码：

I have written the below code for that:

    let btnImg=UIButton.buttonWithType(UIButtonType.Custom) as UIButton
    let img  = UIImage(named: "turn_left") as UIImage
    btnImg.setTitle("Turn left", forState: UIControlState.Normal)
    btnImg.setImage(img, forState: UIControlState.Normal)
    btnImg.frame = CGRectMake(10, 150, 200, 45)
    self.view.addSubview(btnImg)

但是我得到以下错误让img = UIImage（名称：turn_left）为UIImage ：

Swift Compiler error:
 Downcast from 'UIImage?' to 'UIImage' only unwraps optionals; did you mean to use '!'?

推荐答案

因为错误说你必须使用'！'，

As error Says You have to use '!' ,

尝试下面的代码，

   let img  = UIImage(named: "turn_left") as UIImage!  // implicitly unwrapped

OR

   let img : UIImage? = UIImage(named: "turn_left")  //optional

编辑

创建 img 之后，在使用之前需要检查nil。

After creating img you need to check it for nil before using it.

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