在iOS应用中调试MIDI

Question

我正在尝试在我的iOS应用中实现CoreMIDI，现在尝试调试它时遇到了麻烦。 目前，我有一个UILabel，只要我的MIDI回调被调用，它就会更新。 但是，我的UILabel从未更新！ 我不确定为什么会发生这种情况，我猜这是我在MIDI初始化中定义某些内容还是调用UILabel的原因。 我仍在尝试找出答案，但是有更好的方法在iOS应用程序上调试MIDI（因为iOS设备只有一个端口，并且在给定时间只能使用该端口连接到计算机或MIDI控制器） 。

我如何创建MIDI客户端：

Check(MIDIClientCreate(CFSTR("Yun Client"), NULL, NULL , &client));
Check(MIDIOutputPortCreate(client, CFSTR("Yun Output Port"), &outputPort));
Check(MIDIInputPortCreate(client, CFSTR("Yun Input Port"), MIDIInputCallback, 
                         (__bridge void *)self, &inputPort));
unsigned long sourceCount = MIDIGetNumberOfSources();

CFStringRef endpointName;
for (int i = 0; i < sourceCount; ++i) {
    MIDIEndpointRef endPoint = MIDIGetSource(i);
    endpointName = NULL;
    Check(MIDIObjectGetStringProperty(endPoint, kMIDIPropertyName, &endpointName));
    Check(MIDIPortConnectSource(inputPort, endPoint, NULL));
    [param addToMIDIInputsArray:[NSString stringWithFormat:@"%@", endpointName]];
}

我的MIDI回调：

// MIDI receiver callback
static void MIDIInputCallback(const MIDIPacketList *pktlist, 
                              void *refCon, void *connRefCon) {
    SynthViewController *vc = (__bridge SynthViewController*)refCon;

    MIDIPacket *packet = (MIDIPacket *)pktlist->packet;

    Byte midiCommand = packet->data[0] >> 4;
    NSInteger command = midiCommand;

    Byte noteByte = packet->data[1] & 0x7F;
    NSInteger note = noteByte;

    Byte velocityByte = packet->data[2] & 0x7F;
    float velocity = [[NSNumber numberWithInt:velocityByte] floatValue];

    // Note On event
    if (command == 9 && velocity > 0) {
        [vc midiKeyDown:(note+4) withVelocity:velocity];
    } 
    // Note off event
    else if ((command == 9 || command == 8) && velocity == 0) {
        [vc midiKeyUp:(note+4)];
    }

    [vc.logLabel addLogLine:[NSString stringWithFormat:@"%lu - %lu - %lu", 
                            (long)command, (long)note, (long)velocityByte]];
}

addLogLine方法：

- (void)addLogLine:(NSString *)line {
    NSString *str = [NSString stringWithFormat:@"%d - %@", _cnt++, line];
    _logLabel.text = str;
}

任何帮助都很棒！ 谢谢

Answer 1

MIDIInputPortCreate的标头文档中说：

将在CoreMIDI拥有的单独的高优先级线程上调用readProc。

您必须仅在主线程上更新UIKit。

解析传入的MIDI数据后，使用dispatch_async将控制权转移到主线程。

static void MIDIInputCallback(const MIDIPacketList *pktlist, 
                          void *refCon, void *connRefCon) {
    SynthViewController *vc = (__bridge SynthViewController*)refCon;
    // ...

    dispatch_async(dispatch_get_main_queue(), ^{
        // Note On event
        if (command == 9 && velocity > 0) {
           [vc midiKeyDown:(note+4) withVelocity:velocity];
        } 
        // Note off event
        else if ((command == 9 || command == 8) && velocity == 0) {
           [vc midiKeyUp:(note+4)];
        }

        [vc.logLabel addLogLine:[NSString stringWithFormat:@"%lu - %lu - %lu", (long)command, (long)note, (long)velocityByte]];
    });
}