从Objective C将回调/闭包转换为Swift

Question

所以我试图在Swift中实现Superpowered库，并且在回调初始化时遇到困难。我该如何转换该行：

    __unsafe_unretained Superpowered *self = (__bridge Superpowered *)clientdata;

进入斯威夫特？

以下是简化的Objective C实现：

@implementation Superpowered {
    SuperpoweredIOSAudioIO *audioIO;
    SuperpoweredBandpassFilterbank *filters;
    unsigned int samplerate;
}

static bool audioProcessing(void *clientdata, float **buffers, unsigned int inputChannels, unsigned int outputChannels, unsigned int numberOfSamples, unsigned int samplerate, uint64_t hostTime) {
    __unsafe_unretained Superpowered *self = (__bridge Superpowered *)clientdata;
    if (samplerate != self->samplerate) {
        self->samplerate = samplerate;
    };

    // Update position.
    self->lastNumberOfSamples = numberOfSamples;

    return false;
}

- (id)init {
    self = [super init];
    if (!self) return nil;
    samplerate = 44100;

    audioIO = [[SuperpoweredIOSAudioIO alloc] initWithDelegate:(id<SuperpoweredIOSAudioIODelegate>)self preferredBufferSize:12 preferredMinimumSamplerate:44100 audioSessionCategory:AVAudioSessionCategoryRecord channels:2 audioProcessingCallback:audioProcessing clientdata:(__bridge void *)self];
    [audioIO start];

    return self;
}

这是我的Swift版本的开始：

func bridge<T : AnyObject>(obj : T) -> UnsafeMutableRawPointer {
    return UnsafeMutableRawPointer(Unmanaged.passUnretained(obj).toOpaque())
    // return unsafeAddressOf(obj) // ***
}

func bridge<T : AnyObject>(ptr : UnsafeMutableRawPointer) -> T {
    return Unmanaged<T>.fromOpaque(ptr).takeUnretainedValue()
    // return unsafeBitCast(ptr, T.self) // ***
}

open class EchoesEngine: NSObject, CLLocationManagerDelegate, SuperpoweredIOSAudioIODelegate {

    public var audioIO:SuperpoweredIOSAudioIO
    static var lastNumberOfSamples:UInt32!
    static var samplerate:UInt32!

    override init() {
        super.init()
        audioIO = SuperpoweredIOSAudioIO.init(delegate: self, preferredBufferSize: 12, preferredMinimumSamplerate: 44100, audioSessionCategory: AVAudioSessionCategoryPlayAndRecord, channels: 2, audioProcessingCallback: EchoesEngine.audioProcessingCallback, clientdata: bridge(obj: self))
        …
    }

    @objc static let audioProcessingCallback : @convention(c) (UnsafeMutableRawPointer?, UnsafeMutablePointer<UnsafeMutablePointer<Float>?>?, UInt32, UInt32, UInt32, UInt32, UInt64) -> Bool = {
        (clientdata, buffers, inputChannels, outputChannels, numberOfSamples, _samplerate, hostTime) in
        /*
        let unsafePointer = Unmanaged<EchoesEngine>.fromOpaque(clientdata!).takeUnretainedValue()
        let pointer = AutoreleasingUnsafeMutablePointer<EchoesEngine>(unsafePointer)
        */

        self = bridge(ptr: clientdata!)

        if samplerate != _samplerate {
            samplerate = _samplerate
        }

        lastNumberOfSamples = numberOfSamples

        return false
    }

Answer 1

所以我发现在这种情况下，我试图施放的self实际上是一个新变量，提供了__unsafe_unretained对self的引用，传递给SuperpoweredIOSAudioIO的初始化器。

This answer几乎为我提供了所需的一切。 Swift 3.3改变了一些事情，这就是我最终的结果：

func bridge<T : AnyObject>(obj : T) -> UnsafeMutableRawPointer {
    return UnsafeMutableRawPointer(Unmanaged.passUnretained(obj).toOpaque())
    // return unsafeAddressOf(obj) // ***
}

func bridge<T : AnyObject>(ptr : UnsafeMutableRawPointer?) -> T {
    return Unmanaged<T>.fromOpaque(ptr!).takeUnretainedValue()
    // return unsafeBitCast(ptr, T.self) // ***
}