Question

如何在swift

中从本机swift String或NSString创建CFString

    let path:String = NSBundle.mainBundle().pathForResource(name.stringByDeletingPathExtension, ofType:"pdf")
    let string:CFString = ??? path
    let url:CFURLRef = CFURLCreateWithFileSystemPath(allocator:kCFAllocatorDefault, filePath:string, pathStyle:CFURLPathStyle.CFURLPOSIXPathStyle, isDirectory:false)

Answer 1

投下它：

var str = "Hello, playground" as CFString
NSString(format: "type id: %d", CFGetTypeID(str))

Answer 2

如果要转换非文字字符串，则必须将其强制转换为NSString。

let replacement = "World"
let string = "Hello, \(replacement)"

let cfstring:CFString = string as NSString

Swift知道如何将swift字符串转换为NSString，将NSString转换为CFString，但似乎不知道如何在一个中执行这两个步骤。

Answer 3

您可以在CFString和NSString之间或NSString和String之间进行转换。诀窍是你必须在CFString和String之间进行双重演绎。

这有效：

var cfstr: CFString = "Why does Swift require double casting!?"
var nsstr: NSString = cfstr as NSString
var str: String = nsstr as String

这会给出错误＆＃34;＆＃39; CFString＆＃39;不是＆＃39; NSString＆＃39;＆＃34;：

的子类型

var cfstr: CFString = "Why does Swift require double casting!?"
var str: String = cfstr as String

Answer 4

今天我尝试在操场上测试C API并import Foundation使"string" as CFString工作。

Answer 5

如果您正在尝试将包含Swift字符串的变量转换为CFS字符串，我认为@freytag会用他的解释对其进行修改。

如果有人想看一个例子，我想我会包含一个代码片段，我将一个Swift字符串（＆＃34; ArialMT＆＃34;在这种情况下）转换为NSString，以便与之一起使用Core Text的CTFontCreateWithName函数（需要CFString）。（注意：从NSString到CFString的转换是隐式的）。

    // Create Core Text font with desired size
    let coreTextFont:CTFontRef = CTFontCreateWithName("ArialMT" as NSString, 25.0, nil) 

    // Center text horizontally
    var paragraphStyle: NSMutableParagraphStyle = NSMutableParagraphStyle()
    paragraphStyle.alignment = NSTextAlignment.Center

    // Center text vertically
    let fontBoundingBox: CGRect = CTFontGetBoundingBox(coreTextFont)
    let frameMidpoint = CGRectGetHeight(self.frame) / 2
    let textBoundingBoxMidpoint = CGRectGetHeight(fontBoundingBox) / 2
    let verticalOffsetToCenterTextVertically = frameMidpoint - textBoundingBoxMidpoint

    // Create text with the following attributes
    let attributes = [
        NSFontAttributeName : coreTextFont,
        NSParagraphStyleAttributeName: paragraphStyle,
        kCTForegroundColorAttributeName:UIColor.whiteColor().CGColor
    ]
    var attributedString = NSMutableAttributedString(string:"TextIWantToDisplay", attributes:attributes)

    // Draw text (CTFramesetterCreateFrame requires a path).
    let textPath: CGMutablePathRef = CGPathCreateMutable()
    CGPathAddRect(textPath, nil, CGRectMake(0, verticalOffsetToCenterTextVertically, CGRectGetWidth(self.frame), CGRectGetHeight(fontBoundingBox)))
    let framesetter: CTFramesetterRef = CTFramesetterCreateWithAttributedString(attributedString)
    let frame: CTFrameRef = CTFramesetterCreateFrame(framesetter, CFRangeMake(0, attributedString.length), textPath, nil)
    CTFrameDraw(frame, context)

如何将swift String转换为CFString

5 个答案: