从 C 样式指针访问 self [重复]

Question

我正在开发一个使用 MIDI 设备的应用程序。在操场上玩了一些 CoreMIDI 之后，我找到了如何获取 MIDI 输入信号，所以我实现了这个：

func makeInputSource() {
    var midiClient : MIDIClientRef = 0
    var inPort : MIDIPortRef = 0

    MIDIClientCreate("WobClient" as CFString, nil, nil, &midiClient)
    MIDIInputPortCreate(midiClient, "WobClient_InPort" as CFString, {
        (pktList: UnsafePointer<MIDIPacketList>, readProcRefCon: UnsafeMutableRawPointer?, srcConnRefCon: UnsafeMutableRawPointer?) in
        let packetList : MIDIPacketList = pktList.pointee
        var packet : MIDIPacket = packetList.packet

        for _ in 1...packetList.numPackets {
            let bytes = Mirror(reflecting: packet.data).children
            var params : [UInt64] = []

            var i = packet.length
            for (_, attr) in bytes.enumerated() {
                let string = String(format: "%02X ", attr.value as! UInt8)
                params.append(UInt64(strtoul(string, nil, 16)))
                i -= 1

                if (i <= 0) {
                    break
                }
            }

            packet = MIDIPacketNext(&packet).pointee
        }
    }, nil, &inPort)
    MIDIPortConnectSource(inPort, self.source, &self.source)
}

这就像使用信号的魅力。现在，我想使用信号来编辑NSSlider 的值，所以很自然地，我想出的是这样的：

self.slider_one?.integerValue = params[2]

但是，当我尝试这样做时，我收到以下错误：

A C function pointer cannot be formed from a closure that captures context

所以我想知道的是，有没有一种方法可以从该闭包内部访问self，还是有其他方法可以快速使用 MIDI 输入？

谢谢。

--- 编辑： 如题，我修改后的代码：

func makeInputSource() {
    var midiClient : MIDIClientRef = 0
    var inPort : MIDIPortRef = 0
    var observer = UnsafeRawPointer(Unmanaged.passUnretained(self).toOpaque())

    MIDIClientCreate("WobClient" as CFString, nil, nil, &midiClient)
    MIDIInputPortCreate(midiClient, "WobClient_InPort" as CFString, {
        (pktList: UnsafePointer<MIDIPacketList>, readProcRefCon: UnsafeMutableRawPointer?, srcConnRefCon: UnsafeMutableRawPointer?) in
        let packetList : MIDIPacketList = pktList.pointee
        var packet : MIDIPacket = packetList.packet

        for _ in 1...packetList.numPackets {
            let bytes = Mirror(reflecting: packet.data).children
            var params : [UInt64] = []

            var i = packet.length
            for (_, attr) in bytes.enumerated() {
                let string = String(format: "%02X ", attr.value as! UInt8)
                params.append(UInt64(strtoul(string, nil, 16)))
                i -= 1

                if (i <= 0) {
                    break
                }
            }

            let mySelf = Unmanaged<Wob>.fromOpaque(observer).takeUnretainedValue()
            mySelf.slider_one?.integerValue = 25 // 25 is a test value 
            packet = MIDIPacketNext(&packet).pointee
        }

    }, &observer, &inPort)
    MIDIPortConnectSource(inPort, self.source, &self.source)

}

Answer 1

通常你可以将一些上下文传递给 C 函数，例如：

struct MyContext {
   var setSliderValue: (Int) -> Void        
}

var context = MyContext(setSliderValue: { sliderValue in
    Dispatch.queue.async {
       self.slider_one?.integerValue = sliderValue
    }
))

然后将其传递给您的 C 函数：

MIDIInputPortCreate(midiClient, "WobClient_InPort" as CFString, { ... }, &context, &inPort)

在你的闭包函数内部：

let readContext = readProcRefCon!.assumingMemoryBound(to: MyContext.self)
readContext.pointee.setSliderValue(params[2])

（未经测试编写）