How to convert a swift String to CFString

Question

How can i create a CFString from a native swift String or NSString in swift

    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)

In this case, why not just use `let url = NSURL.fileURLWithPath(path, isDirectory:false)` — David Berry, Jun 06 '14 at 20:54
@EricD. I understand, but I think it is an IOS question and not only me, I suppose...thank you — ciccioska, Nov 04 '15 at 18:01

score 51 · Accepted Answer · edited Jan 14 '20 at 08:32

51

Just cast it:

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

Note that you'll need import Foundation for cast as CFString to work.
Otherwise if you only have import CoreFoundation, you'll need to force cast as! CFString.

edited Jan 14 '20 at 08:32

Cœur

37,241
25
195
267

answered Jun 06 '14 at 21:14

MagerValp

2,922
1
24
27

score 29 · Answer 2 · answered Jul 18 '14 at 07:55

29

If you want to convert a non-literal string, you have to cast it to NSString.

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

let cfstring:CFString = string as NSString

Swift knows how to convert a swift string to an NSString and an NSString to a CFString, but seems not to know how to do both steps in one.

answered Jul 18 '14 at 07:55

freytag

4,769
2
27
32

1

I'm hoping that this sort of issue will be improved as Swift evolves! Using Core Foundation from Swift hurts... – John M. P. Knox Jul 30 '14 at 20:24
Still an issue with 1.0 release :( – Tristan Warner-Smith Sep 24 '14 at 17:12

score 5 · Answer 3 · answered Jul 23 '14 at 00:52

5

You cast it between CFString and NSString, or between NSString and String. The trick is that you must double cast when going between CFString and String.

This works:

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

This gives the error "'CFString' is not a subtype of 'NSString'":

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

answered Jul 23 '14 at 00:52

jeremywhuff

2,911
3
29
33

any idea why is that? – Kamchatka Sep 13 '14 at 10:56
I don't know why - it would be much easier if this was not required. I guess that the compiler just hasn't matured enough to make this possible. – jeremywhuff Sep 15 '14 at 16:49

score 5 · Answer 4 · answered Jan 09 '16 at 20:33

5

Today I was trying to do this in a playground for testing a C API and just import Foundation made "string" as CFString work.

answered Jan 09 '16 at 20:33

BoteRock

467
6
12

score 0 · Answer 5 · answered Aug 07 '14 at 22:27

If you're trying to convert a variable that contains a Swift string to a CFString I think @freytag nailed it with his explanation.

In case anyone wanted to see an example I thought I'd include a code snippet where I cast a Swift string ("ArialMT" in this case) to an NSString in order to use it with the CTFontCreateWithName function from Core Text (which requires a CFString). (Note: the cast from NSString to CFString is implicit).

    // 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)

How to convert a swift String to CFString

5 Answers5

Linked