undo drawing code

undoDrawing.java

import java.util.ArrayList;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
 
public class DrawView extends View implements OnTouchListener {
    private Canvas  mCanvas;
    private Path    mPath;
    private Paint       mPaint;   
    private ArrayList<Path> paths = new ArrayList<Path>();
    private ArrayList<Path> undonePaths = new ArrayList<Path>(); 
 
    private Bitmap im;
    public DrawView(Context context) 
    { 
        super(context);
        setFocusable(true);
        setFocusableInTouchMode(true);      
        this.setOnTouchListener(this);
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setColor(0xFFFFFFFF);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeWidth(6);
        mCanvas = new Canvas();
        mPath = new Path();
 
        im=BitmapFactory.decodeResource(context.getResources(),R.drawable.ic_launcher);
 
 
    }                
        @Override 
        protected void onSizeChanged(int w, int h, int oldw, int oldh) {
            super.onSizeChanged(w, h, oldw, oldh);
        } 
 
        @Override 
        protected void onDraw(Canvas canvas) {
            //mPath = new Path(); 
            //canvas.drawPath(mPath, mPaint); 
            for (Path p : paths){
                canvas.drawPath(p, mPaint);
            } 
            canvas.drawPath(mPath, mPaint);
        } 
 
        private float mX, mY;
        private static final float TOUCH_TOLERANCE = 4;
 
        private void touch_start(float x, float y) {
            undonePaths.clear();
            mPath.reset();
            mPath.moveTo(x, y);
            mX = x;
            mY = y;
        } 
        private void touch_move(float x, float y) {
            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;
            } 
        } 
        private void touch_up() { 
            mPath.lineTo(mX, mY);
            // commit the path to our offscreen 
            mCanvas.drawPath(mPath, mPaint);
            // kill this so we don't double draw 
            paths.add(mPath);
            mPath = new Path();            
 
        } 
 
        public void onClickUndo () {  
            if (paths.size()>0) 
            {  
               undonePaths.add(paths.remove(paths.size()-1));
               invalidate();
             } 
            else 
            { 
 
            } 
             //toast the user  
        } 
 
        public void onClickRedo (){ 
           if (undonePaths.size()>0) 
           {  
               paths.add(undonePaths.remove(undonePaths.size()-1)); 
               invalidate();
           }  
           else  
           { 
 
           } 
             //toast the user  
        } 
 
    @Override 
    public boolean onTouch(View arg0, MotionEvent event) {
          float x = event.getX();
          float y = event.getY();
 
          switch (event.getAction()) {
              case MotionEvent.ACTION_DOWN:
                  touch_start(x, y);
                  invalidate();
                  break; 
              case MotionEvent.ACTION_MOVE:
                  touch_move(x, y);
                  invalidate();
                  break; 
              case MotionEvent.ACTION_UP:
                  touch_up(); 
                  invalidate();
                  break; 
          } 
          return true; 
    } 
}