Convert CFString to NSString - Swift
Solution 1
Swift.String and NSString are toll free bridged.
NSString and CFString can be cast to one another, but you can't directly cast from a Swift String to a CFString or vice versa.
Follow these steps to cast from a Core Foundation String to a Swift String:
var cfStr:CFString = "Soon, I'll be a Swift String"
var nsTypeString = cfStr as NSString
var swiftString:String = nsTypeString
Example for CFTypeRef:
var cfStr:CFTypeRef = "Soon, I'll be a Swift String"
var nsTypeString = cfStr as NSString
var swiftString:String = nsTypeString
Solution 2
At least as of Swift 2.0 (verify from a terminal with swift --version
), you can convert a CFString
to a native Swift String
with a simple as String
.
This is sufficient, since Swift's String
type can be used anywhere NSString
is expected.
An example with a kUTType*
constant (kUTType*
constants are defined by CoreServices and are CFString
s):
// Get UTF8 plain text from the pasteboard.
import AppKit
let str = NSPasteboard.generalPasteboard().stringForType(kUTTypeUTF8PlainText as String)
A more detailed example:
// Import at least the Foundation framework.
// Since Cocoa includes Foundation, `import Cocoa` works too.
// (Note that `import CoreServices`, even though it defines type `CFString`,
// is NOT enough - the conversion will fail.)
import Foundation
// Create a CFString.
// The fact that initializing from a `String` literal here works implies that
// the *reverse* cast - String -> CFString - also works.
var cfStr:CFString = "Cast me."
// Convert it to String.
var swiftStr = cfStr as String
To test what type you're dealing with:
cfStr is CFString // true
swiftStr is String // true
To get the string's type, use .dynamicType
; in a string context, this reports the type name but note that you may get the name of a private internal class back:
"cfStr is a \(cfStr.dynamicType) instance."
// -> "cfStr is a _NSContiguousString instance." !!
Still, you can treat this as a CFString
, as the is
test above shows.
Use _stdlib_getDemangledTypeName()
to get the true, underlying class name:
_stdlib_getDemangledTypeName(cfStr) // -> "ObjectC.CFString"
_stdlib_getDemangledTypeName(kUTTypeUTF8PlainText) // ditto
Solution 3
As for me, I like to make extentions and use them afterwards. It seems convenient and clear to read:
Extention:
extension CFString {
var string: String {
return self as String
}
}
Usage:
let specificQueryPart: [String: NSObject] = [
kSecReturnData.string: true as NSObject,
kSecAttrService.string: key as NSObject,
kSecMatchLimit.string: kSecMatchLimitOne
]
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user3185748
Updated on June 14, 2022Comments
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user3185748 about 2 years
I'm trying to write a program that will scan for available serial ports and present them in a popup menu. Why can I not take the
CFString
straight from theIORegistryEntryCreateCFProperty()
function and add it to the menu via string interpolation in the next line? For some reason my variable declaration is met with the error:"NSString is not a subtype of CFString".
import Foundation import Cocoa import IOKit import IOKit.serial @objc class Serial { init() { } @IBOutlet var serialListPullDown : NSPopUpButton! func refreshSerialList(defaultprompt: String) { let masterPort: mach_port_t = kIOMasterPortDefault let classesToMatch: CFDictionary = IOServiceMatching(kIOSerialBSDServiceValue).takeUnretainedValue() var matchingServices: io_iterator_t = 0 // remove everything from the pull down list serialListPullDown?.removeAllItems() // ask for all the serial ports let kernResult = IOServiceGetMatchingServices(masterPort, classesToMatch, &matchingServices) if kernResult == KERN_SUCCESS { // success while (io_object_t() == IOIteratorNext(matchingServices)) { var serialport = IORegistryEntryCreateCFProperty(io_object_t(), kIOCalloutDeviceKey, kCFAllocatorDefault, 0) serialListPullDown?.addItemWithTitle("\(serialport)") } } else { // error } } }
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user3185748 almost 10 yearsSo that would become this? imgur.com/ecm3JHM Because it's returning the same error for me.
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Woodstock almost 10 yearsIORegistryEntryCreateCFProperty returns a CFTypeRef, so you need to declare your var type CFTypeRef not CFString
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Woodstock almost 10 years@user3185748 CFTypeRef is like Any for Core Foundation
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user3185748 almost 10 yearsFirstly, thank you for your patience as I try to wrap my head around this. The suggested CFTypeRef however doesn't appear to fix the issue: imgur.com/DxKrGiX
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Woodstock almost 10 years@user3185748 no problem, OK next lets look at what you are calling IORegistryEntryCreateCFProperty with. What type is kIOCalloutDeviceKey? I think it needs to be a CFString, cast it like this: CFSTR(kIOCalloutDeviceKey)
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user3185748 almost 10 yearsThat seems a little closer, now it's just giving me: "Use of unresolved identifier 'CFSTR'".
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Woodstock almost 10 yearsLet us continue this discussion in chat.
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mklement0 over 8 yearsPerhaps recent changes to Swift changed the behavior: It seems that at least as of Swift version 2.0 you can now convert directly from
CFString
:var swiftString:String = cfStr as String
. Yourvar swiftString:String = nsTypeString
example now needs suffixas String
in order to compile.