Change line color in surface view and keep the previous line color

I followed the tutorial here https://github.com/vivekrk/SurfaceView-Sample and changed it to the code below.

Every time I click the button to change the color, the whole color, including the line that was already present in the view change. I only need a new line to change its color.
How to do it?

I am new to Android and any help would be greatly appreciated. Thanks in Advance.

CanvasView.java

import java.util.ArrayList;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.RectF;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

public class CanvasView extends SurfaceView implements SurfaceHolder.Callback {

    private static final float STROKE_WIDTH = 8;

    private UIThread uiThread;

    private Path mPath;

    public static Paint mPaint;

    private Path oldPath;

    private DrawableObject drawableObject = null;

    private float mX;
    private float mY;
    private float TOUCH_TOLERANCE = 8;

    private RectF dirtyRect;

    private int mMode = Constants.FREE_DRAWING;

    private ArrayList<DrawableObject> objectsToDraw;


    public static int colorofpaint;



    public CanvasView(Context context) {
        super(context);
        getHolder().addCallback(this);

        objectsToDraw = new ArrayList<DrawableObject>();

        mPath = new Path();
    }

    public void clearCanvas() {
        mPath.reset();
    }

    public void setDrawingMode(int drawingMode) {
        mMode = drawingMode;
    }

    @Override
    public void onDraw(Canvas canvas) {
        setPaintProperties();

        if (canvas != null) {
            canvas.drawColor(Color.WHITE);
            synchronized (objectsToDraw) {
                for (DrawableObject drawableObject : objectsToDraw) {
                    drawableObject.draw(canvas);
                }
            }
        }
    }

    public void stopUIThread() {
        uiThread.setRunning(false);
    }

    private void setPaintProperties() {
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        //mPaint.setColor(Color.RED);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeWidth(STROKE_WIDTH);
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width,
            int height) {
        oldPath = mPath;
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        float x = event.getX();
        float y = event.getY();

        switch (mMode) {
        case Constants.FREE_DRAWING:
            drawableObject = new FreeDrawing(mPath, mPaint);

            if (colorofpaint==1) {
                mPaint.setColor(Color.GREEN);
            }

            if (colorofpaint==2) {
                mPaint.setColor(Color.RED);
            }

            if (colorofpaint==3) {
                mPaint.setColor(Color.BLUE);
            }

            if (colorofpaint==4) {
                mPaint.setColor(Color.YELLOW);
            }

            if (colorofpaint==5) {
                mPaint.setColor(Color.CYAN);
            }

            if (colorofpaint==6) {
                mPaint.setColor(Color.BLACK);
            }

            if (colorofpaint==7) {
                mPaint.setColor(Color.MAGENTA);
            }


            break;


        default:
            break;
        }

        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            synchronized (objectsToDraw) {
                objectsToDraw.add(drawableObject);
            }
            mPath.moveTo(x, y);
            mX = x;
            mY = y;
            break;

        case MotionEvent.ACTION_MOVE:
            switch (mMode) {
            case Constants.FREE_DRAWING:
                float dx = Math.abs(x - mX);
                float dy = Math.abs(y - mY);

                if (dx >= TOUCH_TOLERANCE  || dy >= TOUCH_TOLERANCE) {
                    mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);

                    mX = x;
                    mY = y;
                }
                break;
            }
            break;

        case MotionEvent.ACTION_UP:
            switch (mMode) {
            case Constants.FREE_DRAWING:
                mPath.moveTo(x, y);
                break;
            }
            break;
        }
        return true;
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        uiThread = new UIThread(this);
        uiThread.setRunning(true);
        uiThread.start();
    }

    public void restoreOldPath() {
        mPath = oldPath;
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        uiThread.setRunning(false);
    }

    public RectF getDirtyRect() {
        if(dirtyRect == null) {
            dirtyRect = new RectF();
        }
        return dirtyRect ;
    }



}

      

        
        
        
      

    

UIThread.java

import android.graphics.Canvas;
import android.view.SurfaceHolder;

public class UIThread extends Thread {

    private static boolean toRun = false;
    private CanvasView canvasView;
    private SurfaceHolder surfaceHolder;

    public UIThread(CanvasView canvasView) {
        this.canvasView = canvasView;
        surfaceHolder = canvasView.getHolder();
    }

    public boolean isThreadRunning() {
        return toRun;
    }

    public void setRunning(boolean run) {
        toRun = run;
    }

    @Override
    public void run() {
        Canvas c;
        while (toRun) {
                c = null;
                try {
                    c = surfaceHolder.lockCanvas(null);
                    canvasView.onDraw(c);
                } finally {
                    if (c != null) {
                        surfaceHolder.unlockCanvasAndPost(c);
                    }
                }
        }
    }

}

      

        
        
        
      

    

FreeDrawing.java

import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;

public class FreeDrawing extends DrawableObject {

    private Path mPath;
    private Paint mPaint;

    public FreeDrawing(Path path, Paint paint) {
        mPath = path;
        mPaint = paint;
    }

    @Override
    public void draw(Canvas canvas) {
        canvas.drawPath(mPath, mPaint);
    }
}

      

        
        
        
      

    

DrawableObject.java

import android.graphics.Canvas;

public abstract class DrawableObject {

    abstract public void draw(Canvas canvas);

}

      

        
        
        
      

    

.Java constants

public class Constants {
//  XXX:Drawing modes
    public static final int FREE_DRAWING = 1000;
    public static final int LINE_DRAWING = 1001;
    public static final int RECT_DRAWING = 1002;
    public static final int SELECT = 1003;
}

      

        
        
        
      

    

SurfaceViewSampleActivity.java

import android.app.Activity;
import android.content.res.Configuration;
import android.graphics.Color;
import android.graphics.LightingColorFilter;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.FrameLayout;
import android.widget.RadioGroup;
import android.widget.RadioGroup.OnCheckedChangeListener;
import android.widget.Toast;

public class SurfaceViewSampleActivity extends Activity  {
    /** Called when the activity is first created. */
    private CanvasView view;
    private static final int CLEAR = 100;

    private FrameLayout surfaceViewFrame;

    private RadioGroup mode;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);



        surfaceViewFrame = (FrameLayout) findViewById(R.id.surfaceviewFrame);
        view = new CanvasView(this);
        surfaceViewFrame.addView(view, 0);

        CanvasView.colorofpaint=6;


        view.setDrawingMode(Constants.FREE_DRAWING);


        Button b1=(Button)findViewById(R.id.button1);
        b1.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                CanvasView.colorofpaint=2;
        //      view.setDrawingMode(Constants.FREE_DRAWING);
            }
        });



        Button b2=(Button)findViewById(R.id.button2);
        b2.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                CanvasView.colorofpaint=3;

                view.setDrawingMode(Constants.FREE_DRAWING);
            }
        });





    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        menu.add(0, CLEAR, 0, "Clear");
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case CLEAR:
            view.clearCanvas();
            break;
        }
        return true;
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        Toast.makeText(getApplicationContext(), "onConfigurationChanged", Toast.LENGTH_SHORT).show();
    }



}