iOS CoreMIDI跳过MidiPackets

Question

在我的iOS应用程序中实现MIDI时，我遇到了问题，因为接收方回调似乎正在跳过MIDI消息和数据包。我正在使用Midi监视器检查我丢失了哪些MIDI消息，跳过，等等。

因此，百万美元的问题是为什么iOS要跳过某些MIDI消息？有时不会跳过MIDI消息，但有时会跳过MIDI消息。我不知道如何接近调试，因为我已经耗尽了我的大脑在这一点上。

我的接收器代码：

void MidiReceiver(const MIDIPacketList *packets, 
                  void *context, void *sourceContext) {
    dispatch_async(dispatch_get_main_queue(), ^{
    if (packets->numPackets > 0) {
        MIDIPacket *packet = (MIDIPacket *)packets->packet;

        // Loop through total number of packets
        for (int i = 0; i < packets->numPackets; i++) {
            // Go through each packet, iOS sometimes clumps all data into one packet
            // if the MIDI messages are triggered at the same time
            for (int j = 0; j < packet->length; j += 3) {
                NSArray *array = [[NSArray alloc] initWithObjects:[NSNumber numberWithUnsignedInt:packet->data[j]],
                                  [NSNumber numberWithUnsignedInt:packet->data[j+1]],
                                  [NSNumber numberWithUnsignedInt:packet->data[j+2]], nil];

                // Use the data to create do meaningful in the app
                [myViewController processMidiData:array];
            }

            // Next packet
            packet = MIDIPacketNext(packet);
        }
    }
});

监视器代码格式是：(时间)- (MIDI命令类型)- (CC、Val或流速)

Midi监视器调试：

12:45:32.697    Control 0
12:45:32.720    Control 1
12:45:32.737    Control 1
12:45:32.740    Control 2
12:45:32.750    Control 3
12:45:32.763    Note Off    A♯1 0
12:45:32.763    Note Off    F2  0
12:45:32.763    Note Off    D3  0
12:45:32.763    Control 4
12:45:32.770    Control 5
12:45:32.780    Control 6
12:45:32.790    Control 8
12:45:32.800    Control 9
12:45:32.810    Control 11
12:45:32.820    Control 13
12:45:32.832    Control 14
12:45:32.845    Control 16
12:45:32.850    Control 18
12:45:32.873    Control 21
12:45:32.883    Control 22
12:45:32.898    Control 24
12:45:32.913    Control 26
12:45:32.933    Control 27
12:45:32.948    Control 28
12:45:33.020    Control 27
12:45:33.030    Control 26
12:45:33.040    Control 25
12:45:33.050    Control 24
12:45:33.060    Control 22

我的应用程序调试监视器：

12:45:33.050    Control 0
12:45:33.051    Control 1
12:45:33.051    Control 1
12:45:33.051    Control 2
12:45:33.051    Control 3
12:45:33.083    Note Off    D3 0       <----- Where's A#1 and F2!!! :(
12:45:33.087    Control 4
12:45:33.087    Control 4
12:45:33.097    Control 5
12:45:33.100    Control 6
12:45:33.110    Control 8
12:45:33.120    Control 9
12:45:33.130    Control 11
12:45:33.140    Control 13
12:45:33.153    Control 14
12:45:33.165    Control 16
12:45:33.170    Control 18
12:45:33.193    Control 21
12:45:33.203    Control 22
12:45:33.218    Control 24
12:45:33.233    Control 26
12:45:33.256    Control 27
12:45:33.268    Control 28
12:45:33.341    Control 27
12:45:33.351    Control 26
12:45:33.361    Control 25
12:45:33.374    Control 24
12:45:33.381    Control 22

Answer 1

从库尔特·雷维斯那里得到了一些帮助，我似乎因为使用dispatch_async而发送数据包太晚了。

修改后的代码(我首先解析了数据包)：

void MidiReceiver(const MIDIPacketList *packets, 
              void *context, void *sourceContext) {

    NSMutableArray *packetData = [[NSMutableArray alloc] init];

    if (packets->numPackets > 0 && object != nil) {
        MIDIPacket *packet = &packets->packet[0];
        // Loop through total number of packets
        for (int i = 0; i < packets->numPackets; ++i) {
             int idx = 0;
             while (idx < packet->length) {
                 NSArray *array = [[NSArray alloc] initWithObjects:[NSNumber numberWithUnsignedInt:packet->data[idx]],
                                  [NSNumber numberWithUnsignedInt:packet->data[idx+1]],
                                  [NSNumber numberWithUnsignedInt:packet->data[idx+2]], nil];

                [packetData addObject:array];
                idx += 3;
             }
             packet = MIDIPacketNext(packet); 
         }
    }

    dispatch_async(dispatch_get_main_queue(), ^{
        for (NSArray *packet in packetData) {
            [object receiveMIDIInput:packet];
        }
    });
}