CFDictionary get Value for Key in Swift3

Question

I've a problem with accessing a specific (or any) key in a CFDictionary. Honestly I don't really get the way you need to do this in Swift and I think it's overly complicated...

My Code:

if let session = DASessionCreate(kCFAllocatorDefault) {
let mountedVolumes = FileManager.default.mountedVolumeURLs(includingResourceValuesForKeys: [], options: [])!
for volume in mountedVolumes {
    if let disk = DADiskCreateFromVolumePath(kCFAllocatorDefault, session, volume as CFURL) {
        let diskinfo = DADiskCopyDescription(disk);   

        var volumeValue = CFDictionaryGetValue(diskinfo, <#T##key: UnsafeRawPointer!##UnsafeRawPointer!#>)


    }
}

What I want to achieve: Get the Value for the Key or field DAVolumeNetwork into the variable volumeValue. I guess I need to pass the kDADiskDescriptionVolumeNetworkKey to the CFDictionaryGetValue Method? How do I achieve this?

Martin R · Accepted Answer · 2017-03-14T13:33:05.973

Don't use CFDictionary in Swift. (It is possible, but not worth the effort, see below.)

CFDictionary is toll-free bridged with NSDictionary, which in turn can be cast to a Swift Dictionary.
The value of the kDADiskDescriptionVolumeNetworkKey key is a CFBoolean which can be cast to a Swift Bool.

Example:

if let session = DASessionCreate(kCFAllocatorDefault),
    let mountedVolumes = FileManager.default.mountedVolumeURLs(includingResourceValuesForKeys: []) {
    for volume in mountedVolumes {
        if let disk = DADiskCreateFromVolumePath(kCFAllocatorDefault, session, volume as CFURL),
            let diskinfo = DADiskCopyDescription(disk) as? [NSString: Any] {

            if let networkValue = diskinfo[kDADiskDescriptionVolumeNetworkKey] as? Bool {
                print(networkValue)
            }
        }
    }
}

Just for the sake of completeness: This is the necessary pointer juggling to call CFDictionaryGetValue in Swift 3:

if let session = DASessionCreate(kCFAllocatorDefault),
    let mountedVolumes = FileManager.default.mountedVolumeURLs(includingResourceValuesForKeys: []) {
    for volume in mountedVolumes {
        if let disk = DADiskCreateFromVolumePath(kCFAllocatorDefault, session, volume as CFURL),
            let diskinfo = DADiskCopyDescription(disk) {

            if let ptr = CFDictionaryGetValue(diskinfo, Unmanaged.passUnretained(kDADiskDescriptionVolumeNetworkKey).toOpaque()) {
                let networkValue = Unmanaged<NSNumber>.fromOpaque(ptr).takeUnretainedValue()
                print(networkValue.boolValue)
            }
        }
    }
}

Thank you for the explanation and code! I still don't really get the CFDictionary but it's good if it can be cast in something useful :) — nja, Mar 14 '17 at 13:44
@nja: CFDictionary uses a C API, passing void pointers around. In (Objective-)C you can simply pass an object pointer for a void pointer and vice versa. You cannot do that in Swift and have to use the Unmanaged type instead, compare http://stackoverflow.com/questions/33294620/how-to-cast-self-to-unsafemutablepointervoid-type-in-swift. — Martin R, Mar 14 '17 at 13:51
CFDictionary is toll-free bridged with NSDictionary, and this is the easiest/most performant way to get values out in Swift: https://stackoverflow.com/a/45625787/225810 — Gabriel, Aug 11 '17 at 01:59

score 1 · Answer 2 · answered Mar 14 '17 at 13:08

1

You can cast CFDictionaryRef to a Swift dictionary:

if let disk = DADiskCreateFromVolumePath(kCFAllocatorDefault, session, volume as CFURL), let diskinfo = DADiskCopyDescription(disk) as? [String: AnyObject] {
}

and then cast kDADiskDescriptionVolumeNetworkKey to a Swift string:

var volumeValue = diskinfo[kDADiskDescriptionVolumeNetworkKey as String]

answered Mar 14 '17 at 13:08

sbooth

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Casting a CFDictionary to Swift dictionary is expensive (not toll-free bridged). Best to cast to NSDictionary and use that: https://stackoverflow.com/a/45625787/225810 – Gabriel Aug 11 '17 at 02:00

CFDictionary get Value for Key in Swift3

2 Answers2

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