跟踪手指在屏幕上的位置生成音频样本并播放

public class FingerSynthesis extends Activity implements OnTouchListener
{
  AudioSynthesisTask audioSynth;//播放音频样本的线程
  static final float BASE_FREQUENCY = 440;//基准音频频率
  float synth_frequency = BASE_FREQUENCY; // 440 Hz, 随着手指的移动会发生改变
  boolean play = false;//控制是否生成音频样本
  @Override
  public void onCreate(Bundle savedInstanceState)
  {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    View mainView = this.findViewById(R.id.MainView);
    mainView.setOnTouchListener(this);
    audioSynth = new AudioSynthesisTask();
    audioSynth.execute();
  }
  @Override
  public void onPause()
  {
    super.onPause();
    play = false;
    finish();
  }
  public boolean onTouch(View v, MotionEvent event)
  {
    int action = event.getAction();
    switch (action)
    {
      case MotionEvent.ACTION_DOWN:
        play = true;//根据用户操作将play设置为true或者false
        synth_frequency = event.getX() + BASE_FREQUENCY;//跟踪用户手指的位置，做出相应的改变
        Log.v("FREQUENCY", "" + synth_frequency);
        break;
      case MotionEvent.ACTION_MOVE:
        play = true;
        synth_frequency = event.getX() + BASE_FREQUENCY;
        Log.v("FREQUENCY", "" + synth_frequency);
        break;
      case MotionEvent.ACTION_UP:
        play = false;
        break;
      case MotionEvent.ACTION_CANCEL:
        break;
      default:
        break;
    }
    return true;
  }
  private class AudioSynthesisTask extends AsyncTask<Void, Void, Void>
  {
    @Override
    protected Void doInBackground(Void... params)
    {
      final int SAMPLE_RATE = 11025;
      int minSize = AudioTrack.getMinBufferSize(SAMPLE_RATE,
          AudioFormat.CHANNEL_CONFIGURATION_MONO,
          AudioFormat.ENCODING_PCM_16BIT);
      AudioTrack audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC,
          SAMPLE_RATE, AudioFormat.CHANNEL_CONFIGURATION_MONO,
          AudioFormat.ENCODING_PCM_16BIT, minSize,
          AudioTrack.MODE_STREAM);
      audioTrack.play();
      short[] buffer = new short[minSize];
      float angle = 0;
      while (true)
      {
        if (play)
        {
          for (int i = 0; i < buffer.length; i++)
          {
            float angular_frequency = (float) (2 * Math.PI)
                * synth_frequency / SAMPLE_RATE;
            buffer[i] = (short) (Short.MAX_VALUE * ((float) Math
                .sin(angle)));//生成音频样本
            angle += angular_frequency;
          }
          audioTrack.write(buffer, 0, buffer.length);
        } else
        {
          try
          {
            Thread.sleep(50);
          } catch (InterruptedException e)
          {
            e.printStackTrace();
          }
        }
      }
    }
  }
}