Question

我是从iOS教程中学到的，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不能与＆＃39; @lvalue String＆＃39;
构建

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, kUTTypeImage, 0) == CFComparisonResult.CompareEqualTo) {
        editedImage = info.objectForKey(UIImagePickerControllerEditedImage) as UIImage
        originalImage = info.objectForKey(UIImagePickerControllerOriginalImage) as UIImage

它提醒我

无法转换表达式＆＃39; CFString＆＃39;输入＆＃39; $ T1＆＃39;

Answer 1

Swift.String和NSString自动桥接，NSString和CFString可以相互投射，但你不能（现在？）过渡到所有的从Swift String到CFString的方式，无需额外演员或两次。

这是一个Swift字符串，一个带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)

请注意，您不需要在Swift中使用CFStringRef（并且CFString API的大多数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）对象一样处理这些类型。

Answer 2

var str = "string"
var cfstr:CFString = str as NSString // OR str.__conversion()

如何在Swift中将String类型变量转换为CFString？

2 个答案: