SCNetworkReachabilitySetCallback failing in Swift

Question

I'm attempting to use the following code to set a callback for an SCNetworkReachability

// Create callback
let callback:(SCNetworkReachability!, SCNetworkReachabilityFlags, UnsafeMutablePointer<Void>) -> () = { (target: SCNetworkReachability!, flags: SCNetworkReachabilityFlags, info: UnsafeMutablePointer<Void>) in
    // Do something
}

// Create UnsafeMutablePointer and initialise with callback
let p = UnsafeMutablePointer<(SCNetworkReachability!, SCNetworkReachabilityFlags, UnsafeMutablePointer<Void>) -> Void>.alloc(1)
p.initialize(callback)

// convert UnsafeMutablePointer to COpaquePointer
let cp = COpaquePointer(p) 

// convert COppaquePointer to CFunctionPointer
let fp = CFunctionPointer<(SCNetworkReachability!, SCNetworkReachabilityFlags, UnsafeMutablePointer<Void>) -> Void>(cp)

if SCNetworkReachabilitySetCallback(reachability, fp, nil) != 0 {

    println(SCError()) // SCError() is returning 0
}

The SCNetworkReachabilitySetCallback call is failing - has anyone else had any success with this? Any idea where this might be wrong?

Answer 1

As of swift 1.2 you cannot pass functions written in swift using CFunctionPointer. It has mainly been introduced for passing around function pointers already defined in C to some other C (or objectiveC) routines.

One possible work around would be to use objc_block in swift eg:

    let block: @objc_block (SCNetworkReachabilityRef, SCNetworkReachabilityFlags, UnsafePointer<Void>) -> Void = {
        [weak self]
        (reachability: SCNetworkReachabilityRef, flags: SCNetworkReachabilityFlags, data: UnsafePointer<Void>) in

        // Do something e.g. check if network reachability has changed

        if flags & SCNetworkReachabilityFlags(kSCNetworkReachabilityFlagsReachable) == 0 {

        }
    }

    let blockObject = imp_implementationWithBlock(unsafeBitCast(block, AnyObject.self))
    let fp = unsafeBitCast(blockObject, SCNetworkReachabilityCallBack.self)

    // e.g. you can use 169.254.0.0 for local wifi connection

    var reachability = SCNetworkReachabilityCreateWithName(kCFAllocatorDefault, ("169.254.0.0" as NSString).UTF8String).takeRetainedValue()
    var context = SCNetworkReachabilityContext()

    if SCNetworkReachabilitySetCallback(reachability!, fp, &context) == 1 {
        if SCNetworkReachabilityScheduleWithRunLoop(reachability!, CFRunLoopGetCurrent(), NSDefaultRunLoopMode) == 0 {
            println(SCError())
        }
    }

Answer 2

The SCNetworkReachabilitySetCallback function returns a Boolean.

https://developer.apple.com/LIBRARY/ios/documentation/SystemConfiguration/Reference/SCNetworkReachabilityRef/index.html#//apple_ref/c/func/SCNetworkReachabilitySetCallback

The TRUE value is typically defined as 1.

Thus

if SCNetworkReachabilitySetCallback(reachability, fp, nil) != 0 {

    println(SCError()) // SCError() is returning 0
}

would likely only ever print 0.