Objective c MIDISend：在iPhone上播放音符

我正在尝试生成一个音符，使用Objective-C和MIDI通过iPhone扬声器播放。我有下面的代码，但它没有做任何事情。我做错了什么

MIDIPacketList packetList;

packetList.numPackets = 1;

MIDIPacket* firstPacket = &packetList.packet[0];

firstPacket->timeStamp = 0; // send immediately

firstPacket->length = 3;

firstPacket->data[0] = 0x90;

firstPacket->data[1] = 80;

firstPacket->data[2] = 120;

MIDIPacketList pklt=packetList;

MIDISend(MIDIGetSource(0), MIDIGetDestination(0), &pklt);

---

你有三个问题：

声明

MIDIPacketList

不会分配内存或初始化结构

您正在将MIDIGetSource的结果（它返回一个

MIDIEndpointRef

）作为第一个参数传递到

MIDISend

，在那里它需要一个

MIDIPortRef

。（您可能忽略了有关此问题的编译器警告。永远不要忽略编译器警告。）

在iOS中发送MIDI音符不会发出任何声音。如果您没有将外部MIDI设备连接到iOS设备，则需要使用CoreAudio设置可以生成声音的设备。这超出了这个答案的范围

因此，此代码将运行，但除非您有外部硬件，否则不会发出任何声音：

//Look to see if there's anything that will actually play MIDI notes
NSLog(@"There are %lu destinations", MIDIGetNumberOfDestinations());

// Prepare MIDI Interface Client/Port for writing MIDI data:
MIDIClientRef midiclient = 0;
MIDIPortRef midiout = 0;
OSStatus status;
status = MIDIClientCreate(CFSTR("Test client"), NULL, NULL, &midiclient);
if (status) {
    NSLog(@"Error trying to create MIDI Client structure: %d", (int)status);
}
status = MIDIOutputPortCreate(midiclient, CFSTR("Test port"), &midiout);
if (status) {
    NSLog(@"Error trying to create MIDI output port: %d", (int)status);
}

Byte buffer[128];
MIDIPacketList *packetlist = (MIDIPacketList *)buffer;
MIDIPacket *currentpacket = MIDIPacketListInit(packetlist);
NSInteger messageSize = 3; //Note On is a three-byte message
Byte msg[3] = {0x90, 80, 120};
MIDITimeStamp timestamp = 0;
currentpacket = MIDIPacketListAdd(packetlist, sizeof(buffer), currentpacket, timestamp, messageSize, msg);
MIDISend(midiout, MIDIGetDestination(0), packetlist);