我希望有人可以帮助我使用 Xcode 8 和 swift 3 我有一个 Playground 文件 Xcode 7 swift 2，它涉及 Midi 输入的 Midi 回调，在 7 中一切正常

我尝试转换为 8，它引发了关于内存的错误和一些我认为不严重的名称更改，我还使用 PlaygroundSupport 重新定义了无限循环 但是我无法克服的错误涉及 MyMIDIReadProc at

MIDIInputPortCreate(midiClient, "MidiTest_InPort", MyMIDIReadProc, nil, &inPort);

错误说 无法将类型“(pktList: UnsafePointer, readProcRefCon: UnsafeMutablePointer, srcConnRefCon: UnsafeMutablePointer) -> Void”的值转换为预期的参数类型“MIDIReadProc”(又名“@convention(c) (UnsafePointer, Optional>, Optional>) -> ( )')

我的理解是它需要插入一些描述的@convention(c) 包装器。我认为我走在正确的轨道上，因为你可以包装一个函数，但我对把它放在哪里的知识已经用完了。我再次希望有人能提供建议

感谢阅读 由于我是自学的，所以对任何不好的语言表示歉意

这是原始的 Xcode 7 代码

            import Cocoa
            import CoreMIDI
            import XCPlayground

            func getDisplayName(obj: MIDIObjectRef) -> String
            {
                var param: Unmanaged<CFString>?
                var name: String = "Error";

                let err: OSStatus = MIDIObjectGetStringProperty(obj, kMIDIPropertyDisplayName, &param)
                if err == OSStatus(noErr)
                {
                    name =  param!.takeRetainedValue() as String
                }

                return name;
            }

            func MyMIDIReadProc(pktList: UnsafePointer<MIDIPacketList>,
                readProcRefCon: UnsafeMutablePointer<Void>, srcConnRefCon: UnsafeMutablePointer<Void>) -> Void
            {
                let packetList:MIDIPacketList = pktList.memory;
                let srcRef:MIDIEndpointRef = UnsafeMutablePointer<MIDIEndpointRef>(COpaquePointer(srcConnRefCon)).memory;
                print("MIDI Received From Source: \(getDisplayName(srcRef))");

                var packet:MIDIPacket = packetList.packet;
                for _ in 1...packetList.numPackets
                {
                    let bytes = Mirror(reflecting: packet.data).children;
                    var dumpStr = "";
                    // bytes mirror contains all the zero values in the ridiulous packet data tuple
                    // so use the packet length to iterate.
                    var i = packet.length;
                    for (_, attr) in bytes.enumerate()
                    {
                         dumpStr += String(format:"$%02X ", attr.value as! UInt8);
                        --i;
                        if (i <= 0)
                        {
                           break;
                        }
                    }

                    print(dumpStr)
                    packet = MIDIPacketNext(&packet).memory;
                }
            }

            var midiClient: MIDIClientRef = 0;
            var inPort:MIDIPortRef = 0;
            var src:MIDIEndpointRef = MIDIGetSource(0);

            MIDIClientCreate("MidiTestClient", nil, nil, &midiClient);
            MIDIInputPortCreate(midiClient, "MidiTest_InPort", MyMIDIReadProc, nil, &inPort);

            MIDIPortConnectSource(inPort, src, &src);

            // Keep playground running
            XCPlaygroundPage.currentPage.needsIndefiniteExecution = true;

这是转换后的 Xcode 8 代码

            var str = "Hello, playground"
            import Cocoa
            import CoreMIDI
            import XCPlayground
            import PlaygroundSupport


             func getDisplayName(obj: MIDIObjectRef) -> String
             {
             var param: Unmanaged<CFString>?
             var name: String = "Error";

             let err: OSStatus = MIDIObjectGetStringProperty(obj, kMIDIPropertyDisplayName, &param)
             if err == OSStatus(noErr)
             {
             name =  param!.takeRetainedValue() as String
             }

             return name;
             }


            func MyMIDIReadProc(pktList: UnsafePointer<MIDIPacketList>,
                                readProcRefCon: UnsafeMutablePointer<Void>, srcConnRefCon: UnsafeMutablePointer<Void>) -> Void
             {


             let packetList:MIDIPacketList = pktList.pointee;

             let srcRef:MIDIEndpointRef = UnsafeMutablePointer<MIDIEndpointRef>(OpaquePointer(srcConnRefCon)).pointee;
             print("MIDI Received From Source: \(getDisplayName(obj: srcRef))");

             var packet:MIDIPacket = packetList.packet;
             for _ in 1...packetList.numPackets
             {
             let bytes = Mirror(reflecting: packet.data).children;
             var dumpStr = "";

             var i = packet.length;
             for (_, attr) in bytes.enumerated()
             {
             dumpStr += String(format:"$%02X ", attr.value as! UInt8);
             i -= 1;
             if (i <= 0)
             {
             break;
             }

             }

             print(dumpStr)
             packet = MIDIPacketNext(&packet).pointee;
             }
             }

            var midiClient: MIDIClientRef = 0;
             var inPort:MIDIPortRef = 0;
             var src:MIDIEndpointRef = MIDIGetSource(0);

             MIDIClientCreate("MidiTestClient", nil, nil, &midiClient);

             MIDIInputPortCreate(midiClient, "MidiTest_InPort", MyMIDIReadProc, nil, &inPort);

            MIDIPortConnectSource(inPort, src, &src);


             PlaygroundPage.current.needsIndefiniteExecution = true

最佳答案

指针类型在 Swift 3 中发生了巨大变化。许多基于 C 的 API 的签名也相应地发生了变化。

手动执行这些更改会很痛苦。您可以让 Swift 为您工作，只需稍作修改。

尝试更改函数头:

func MyMIDIReadProc(pktList: UnsafePointer<MIDIPacketList>,
                                readProcRefCon: UnsafeMutablePointer<Void>, srcConnRefCon: UnsafeMutablePointer<Void>) -> Void
             {

闭包声明:

let MyMIDIReadProc: MIDIReadProc = {pktList, readProcRefCon, srcConnRefCon in

Swift 以这种方式完美地推断参数类型。

您可能需要修复指针类型转换:

    let srcRef:MIDIEndpointRef = UnsafeMutablePointer<MIDIEndpointRef>(OpaquePointer(srcConnRefCon)).pointee;

像这样:

    //I'm not sure using `!` is safe here...
    let srcRef: MIDIEndpointRef = UnsafeMutablePointer(srcConnRefCon!).pointee

(顺便说一句，你的 Xcode 7 代码中的等效部分有点多余。你不需要在那里使用中间 COpaquePointer。)

在 Swift 3 中，指针不能为 nil，可空指针用 Optionals 表示。您可能需要许多其他修复才能在 Swift 3 中使用基于 C 的 API。

关于xcode - Swift 2 到 swift 3 转换 Midi 输入，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/38258368/