如何在Swift中将String类型变量转换为CFString？

概述我从iOS教程中学到了这一点,但它不起作用 func imagePickerController(picker: UIImagePickerController!, didFinishPickingMediaWithInfo info: NSDictionary!) { var mediaType = info.objectForKey(UIImagePickerControllerMed 我从iOS教程中学到了这一点,但它不起作用

func imagePickerController(picker: UIImagePickerController!,dIDFinishPickingMediawithInfo info: NSDictionary!) {    var mediaType = info.objectForKey(UIImagePickerControllerMediaType) as String    var originalimage,editedImage,imagetoUse: UIImage    // Handle a still image picked from a photo album    if (CFStringCompare(CFStringRef(mediaType),kUTTypeImage,0) == CFComparisonResult.CompareEqualTo) {        editedImage = info.objectForKey(UIImagePickerControllerEditedImage) as UIImage        originalimage = info.objectForKey(UIImagePickerControllerOriginalimage) as UIImage        if (editedImage) {            imagetoUse = editedImage        } else {            imagetoUse = originalimage        }        // Do something with imagetoUse    }

它经常提醒我

CFStringRef is not constructible with ‘@lvalue String’

所以我尝试了这个：

// Handle a still image picked from a photo album    var temp = mediaType as CFString    if (CFStringCompare(temp,0) == CFComparisonResult.CompareEqualTo) {        editedImage = info.objectForKey(UIImagePickerControllerEditedImage) as UIImage        originalimage = info.objectForKey(UIImagePickerControllerOriginalimage) as UIImage

它提醒我

Cannot convert the Expression’s type ‘CFString’ to type ‘$T1’

解决方法 Swift.String和Nsstring自动桥接,Nsstring和CFString可以相互转换,但你不能(现在？)传递上从Swift字符串一直到CFString,而不需要额外的强制转换.

这是一个Swift字符串,一个接受CFString的函数,以及如何通过强制转换为Nsstring来调用它：

var str = "Hello,playground"func takesCFString(s: CFString) {}takesCFString(str as Nsstring)

注意,您不需要使用CFStringRefin Swift(而且大多数CFString API的Swift声明都没有).编译器利用Xcode 5引入的CF类型的自动ARC桥接,让您可以像Swift(或ObjC)对象那样处理这些类型.

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