如何在 UIImagePickerController MediaType 上使用 switch 语句？

Question

如何在 UIImagePickerControllerMediaType 上使用 switch 语句？

以下示例抛出奇怪的编译器错误：

Expression pattern of type 'CFString' cannot match values of type 'CFString'.

func imagePickerController(picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : AnyObject]) {

    switch info[UIImagePickerControllerMediaType] as! CFString {

    case kUTTypeImage:
        break

    default:
        break
    }
}

Answer 1

我可以建议两种方法来解决这个不便。

转换为字符串

简单，但需要额外输入。

func imagePickerController(picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : AnyObject]) {

    switch info[UIImagePickerControllerMediaType] as! String {
        case String(kUTTypeImage):
            break
        default:
            break
    }
}

为 CFString 类型实现模式匹配运算符

更棘手，但如果您需要经常打开CFString，则输入更少。

func imagePickerController(picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : AnyObject]) {

    switch info[UIImagePickerControllerMediaType] as! CFString {
        case kUTTypeImage:
            break
        default:
            break
    }
}

func ~=(pattern: CFString, value: CFString) -> Bool {
    return pattern == value
}

参见语言参考 (Swift 2.2) Patterns 章节中的 "Expression Pattern" 部分。

Answer 2

解决此问题的另一种方法是转换为 NSString:

func imagePickerController(picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : AnyObject]) {

    switch info[UIImagePickerControllerMediaType] as! NSString {
        case kUTTypeImage:
            break
        default:
            break
    }
}