如何在UIImagePickerControllerMediaType上使用switch语句？

Question

如何在UIImagePickerControllerMediaType上使用switch语句？

下面的示例引发的怪编译器错误：

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

我可以建议两种方式来解决这种不便。

投到字符串

很简单，但需要额外的打字。

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

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

为CFString字符串类型

更棘手，但少打字实现模式匹配运营商如果您需要经常CFString切换。

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 
} 

见 “表达模式” 在语言参考Patterns章（SWIFT 2.2）。

Answer 2

另一种方式来解决，这是铸造NSString：

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

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