请帮我用Android语法写一个录制midi文件的demo

好的，以下是一个简单的Android录制MIDI文件的demo，你可以参考一下：

1. 在Android Studio中创建一个新的项目
2. 在MainActivity.java文件中添加以下代码：

import android.media.midi.MidiDeviceInfo;
import android.media.midi.MidiDevice;
import android.media.midi.MidiManager;
import android.media.midi.MidiOutputPort;
import android.media.midi.MidiReceiver;
import android.os.Bundle;
import android.util.Log;

import androidx.appcompat.app.AppCompatActivity;

import java.io.IOException;

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MidiRecorder";

    private MidiManager mMidiManager;
    private MidiDevice mMidiDevice;
    private MidiOutputPort mMidiOutputPort;
    private MidiRecorder mMidiRecorder;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mMidiManager = (MidiManager) getSystemService(MIDI_SERVICE);
        if (mMidiManager == null) {
            Log.e(TAG, "MIDI not supported on this device");
            return;
        }

        MidiDeviceInfo[] infos = mMidiManager.getDevices();
        if (infos.length == 0) {
            Log.e(TAG, "No MIDI devices found");
            return;
        }

        // Choose the first device
        mMidiDevice = mMidiManager.openDevice(infos[0], null);
        if (mMidiDevice == null) {
            Log.e(TAG, "Failed to open MIDI device");
            return;
        }

        // Get the first output port
        mMidiOutputPort = mMidiDevice.getOutputPort(0);
        if (mMidiOutputPort == null) {
            Log.e(TAG, "Failed to open MIDI output port");
            return;
        }

        // Create a MIDI recorder
        mMidiRecorder = new MidiRecorder(mMidiOutputPort);

        // Start recording
        try {
            mMidiRecorder.startRecording();
        } catch (IOException e) {
            Log.e(TAG, "Failed to start recording", e);
            return;
        }

        // Wait for 30 seconds
        try {
            Thread.sleep(30000);
        } catch (InterruptedException e) {
            Log.e(TAG, "Interrupted while sleeping", e);
        }

        // Stop recording
        try {
            mMidiRecorder.stopRecording();
        } catch (IOException e) {
            Log.e(TAG, "Failed to stop recording", e);
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();

        if (mMidiRecorder != null) {
            try {
                mMidiRecorder.stopRecording();
            } catch (IOException e) {
                Log.e(TAG, "Failed to stop recording", e);
            }
        }

        if (mMidiOutputPort != null) {
            mMidiOutputPort.close();
        }

        if (mMidiDevice != null) {
            mMidiDevice.close();
        }
    }

    private static class MidiRecorder implements MidiReceiver {
        private static final int BUFFER_SIZE = 1024;

        private final MidiOutputPort mOutputPort;
        private final byte[] mBuffer;
        private final long[] mTimestamps;
        private int mCount;

        public MidiRecorder(MidiOutputPort outputPort) {
            mOutputPort = outputPort;
            mBuffer = new byte[BUFFER_SIZE];
            mTimestamps = new long[BUFFER_SIZE];
            mCount = 0;
        }

        public void startRecording() throws IOException {
            mOutputPort.connect(this);
        }

        public void stopRecording() throws IOException {
            mOutputPort.disconnect(this);
        }

        @Override
        public void onSend(byte[] data, int offset, int count, long timestamp) throws IOException {
            if (mCount + count > BUFFER_SIZE) {
                Log.w(TAG, "Buffer overflow");
                mCount = 0;
            }

            System.arraycopy(data, offset, mBuffer, mCount, count);
            mTimestamps[mCount] = timestamp;
            mCount += count;
        }

        public void saveToFile(String filename) throws IOException {
            // TODO: Save the MIDI data to a file
        }
    }
}

3. 在AndroidManifest.xml文件中添加以下权限：

<uses-permission android:name="android.permission.RECORD_AUDIO" />
<uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS" />

请注意，这只是一个简单的demo，你需要根据自己的需求对代码进行修改和完善。如果你遇到了问题，可以在评论区提问。