Just trying to send RGB values via three sliders in an Android App. I do not understand how many bytes I need to send as Latch.

MainActivity

package ioio.bosioio;

import ioio.lib.api.SpiMaster;
import ioio.lib.api.exception.ConnectionLostException;
import ioio.lib.util.BaseIOIOLooper;
import ioio.lib.util.IOIOLooper;
import ioio.lib.util.android.IOIOActivity;
import android.os.Bundle;
import android.view.Menu;
import android.widget.SeekBar;
import android.widget.SeekBar.OnSeekBarChangeListener;


public class MainActivity extends IOIOActivity {
  int red_ = 0;
	int green_ = 0;
	int blue_ = 0;
	int numLEDS = 12;
	byte[] buffer1_ = new byte[48];
	byte[] buffer2_ = new byte[48];



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

		// The first seekbar controls the RED.
		final SeekBar redBar = (SeekBar) findViewById(R.id.redBar);
		updateRed(redBar, redBar.getProgress());
		redBar.setOnSeekBarChangeListener(new OnSeekBarChangeListener() {
			@Override
			public void onStopTrackingTouch(SeekBar seekBar) {
			}

			@Override
			public void onStartTrackingTouch(SeekBar seekBar) {
			}

			@Override
			public void onProgressChanged(SeekBar seekBar, int progress,
					boolean fromUser) {
				updateRed(seekBar, progress);
			}
		});

		// The second seekbar controls the GREEN
		final SeekBar greenBar = (SeekBar) findViewById(R.id.greenBar);
		updateGreen(greenBar, greenBar.getProgress());
		greenBar.setOnSeekBarChangeListener(new OnSeekBarChangeListener() {
			@Override
			public void onStopTrackingTouch(SeekBar seekBar) {
			}

			@Override
			public void onStartTrackingTouch(SeekBar seekBar) {
			}

			@Override
			public void onProgressChanged(SeekBar seekBar, int progress,
					boolean fromUser) {
				updateGreen(seekBar, progress);
			}
		});
		//Blue
		final SeekBar blueBar = (SeekBar) findViewById(R.id.blueBar);
		updateBlue(blueBar, blueBar.getProgress());
		blueBar.setOnSeekBarChangeListener(new OnSeekBarChangeListener() {
			@Override
			public void onStopTrackingTouch(SeekBar seekBar) {
			}

			@Override
			public void onStartTrackingTouch(SeekBar seekBar) {
			}

			@Override
			public void onProgressChanged(SeekBar seekBar, int progress,
					boolean fromUser) {
				updateBlue(seekBar, progress);
			}
		});		

	}


	@Override
	protected void onStart() {
		super.onStart();
	}

	@Override
	protected void onStop() {
		super.onStop();
	}

	/** An RGB triplet. */
	private static class RGB {
		byte r;
		byte g;
		byte b;

		RGB(byte r, byte g, byte b) {
			this.r = r;
			this.g = g;
			this.b = b;
		}

		RGB() {
			clear();
		}

		public void clear() {
			r = g = b = 0;
		}
	}

	class IOIOThread extends BaseIOIOLooper {
		private SpiMaster spi_;

		@Override
		protected void setup() throws ConnectionLostException {
			spi_ = ioio_.openSpiMaster(5, 4, 3, 6, SpiMaster.Rate.RATE_50K);
		}

		@Override
		public void loop() throws ConnectionLostException {

			for (int i = 0; i < numLEDS; i++) {
				RGB tmpRGB = new RGB();
				tmpRGB.r =  (byte) (128 - (red_/2)*-1);
				tmpRGB.g =  (byte) (128 - (green_/2)*-1);
				tmpRGB.b =  (byte) (128 - (blue_/2)*-1);
				setLed(i, tmpRGB);
			}

			byte[] latch = new byte[] {0,0}; //latch! Huh?
			try{
				ioio_.beginBatch();   
				spi_.writeRead(0, buffer1_, buffer1_.length,buffer1_.length, null, 0);
				spi_.writeRead(0, latch, latch.length,latch.length, null, 0);
				ioio_.endBatch();
			} catch (InterruptedException e1) {
			}
		}
	}
	
	@Override
	protected IOIOLooper createIOIOLooper() {
		return new IOIOThread();
	}

	/**
	 * Set an LED to a certain color.
	 */
	private void setLed(int num, RGB rgb) {
		// Find the right buffer to write to (first or second half).
		byte[] buffer;
		if (num >= 16) {
			buffer = buffer2_;
			num -= 16;
		} else {
			buffer = buffer1_;
		}
		num *= 3;

		buffer[num++] = rgb.g;
		buffer[num++] = rgb.r;
		buffer[num++] = rgb.b;
	}

	/** Read the progress bar value and scale to [0-1]. */
	private void updateRed(SeekBar seekBar, int progress) {
		//frequency_ = Math.pow((double) progress / seekBar.getMax(), 2.0);
		red_ = progress;
	}

	/** Read the progress bar value and scale to [0-1]. */
	private void updateGreen(SeekBar seekBar, int progress) {
		//fadeRate_ = Math.pow((double) progress / seekBar.getMax(), 2.0);
		green_ = progress;
	}

	/** Read the progress bar value and scale to [0-1]. */
	private void updateBlue(SeekBar seekBar, int progress) {
		//fadeRate_ = Math.pow((double) progress / seekBar.getMax(), 2.0);
		blue_ = progress;
	}

}