Get Canvas coordinates after scaling up/down or dragging in android

I'm developing an application in which I'm pasting images, doing drawing and painting on canvas. This app can also Scale up/down the canvas or drag it to different location.
My problem is: I can't get the correct canvas coordinates after scaling or dragging the canvas. I want to draw finger paint after the canvas is scaled or dragged but unable to retrieve the right place where i've touched..:(
Also I'm new bee. Here is the code.

@Override
 public void onDraw(Canvas canvas) {
     super.onDraw(canvas);
 
     canvas.save();
     //canvas.translate(mPosX, mPosY);
     canvas.scale(mScaleFactor, mScaleFactor, super.getWidth() * 0.5f,
             super.getHeight() * 0.5f);
     mIcon.draw(canvas);
     for (Path path : listPath) {
         canvas.drawPath(path, paint);
     }
     canvas.restore();
 }
 
 public TouchExampleView(Context context, AttributeSet attrs, int defStyle) {
     super(context, attrs, defStyle);
 
 }
 
 @Override
 public boolean onTouchEvent(MotionEvent ev) {
     // Let the ScaleGestureDetector inspect all events.
     mScaleDetector.onTouchEvent(ev);
 
     final int action = ev.getAction();
     switch (action & MotionEvent.ACTION_MASK) {
     case MotionEvent.ACTION_DOWN: {
         final float x = ev.getX();
         final float y = ev.getY();
 
         mLastTouchX = x;
         mLastTouchY = y;
         mActivePointerId = ev.getPointerId(0);
         break;
     }
 
     case MotionEvent.ACTION_MOVE: {
         final int pointerIndex = ev.findPointerIndex(mActivePointerId);
         final float x = ev.getX(pointerIndex);
         final float y = ev.getY(pointerIndex);
 
         // Only move if the ScaleGestureDetector isn't processing a gesture.
         if (!mScaleDetector.isInProgress()) {
             final float dx = x - mLastTouchX;
             final float dy = y - mLastTouchY;
 
             mPosX += dx;
             mPosY += dy;
 
             invalidate();
         }
 
         mLastTouchX = x;
         mLastTouchY = y;
 
         break;
     }
 
     case MotionEvent.ACTION_UP: {
         mActivePointerId = INVALID_POINTER_ID;
         break;
     }
 
     case MotionEvent.ACTION_CANCEL: {
         mActivePointerId = INVALID_POINTER_ID;
         break;
     }
 
     case MotionEvent.ACTION_POINTER_UP: {
         final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
         final int pointerId = ev.getPointerId(pointerIndex);
         if (pointerId == mActivePointerId) {
             // This was our active pointer going up. Choose a new
             // active pointer and adjust accordingly.
             final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
             mLastTouchX = ev.getX(newPointerIndex);
             mLastTouchY = ev.getY(newPointerIndex);
             mActivePointerId = ev.getPointerId(newPointerIndex);
         }
         break;
     }
     }
 
     float objectNewX,objectNewY;
     if (mScaleFactor >= 1) {
         objectNewX = ev.getX() + (ev.getX() - super.getWidth() * 0.5f) * (mScaleFactor - 1);
         objectNewY = ev.getY() + (ev.getY() - super.getHeight() * 0.5f) * (mScaleFactor - 1);
     } else {
         objectNewX = ev.getX() - (ev.getX() - super.getWidth() * 0.5f) * (1 - mScaleFactor);
         objectNewY = ev.getY() - (ev.getY() - super.getHeight() * 0.5f) * (1 - mScaleFactor);
     }
 
     if (ev.getAction() == MotionEvent.ACTION_DOWN) {
         path = new Path();
         path.moveTo(objectNewX,objectNewY);
         path.lineTo(objectNewX,objectNewY);
     } else if (ev.getAction() == MotionEvent.ACTION_MOVE) {
         path.lineTo(objectNewX,objectNewY);
         listPath.add(path);
     } else if (ev.getAction() == MotionEvent.ACTION_UP) {
         path.lineTo(objectNewX,objectNewY);
         listPath.add(path);
     }
 
     return true;
 }
 
 private class ScaleListener extends
         ScaleGestureDetector.SimpleOnScaleGestureListener {
     @Override
     public boolean onScale(ScaleGestureDetector detector) {
         mScaleFactor *= detector.getScaleFactor();
 
         // Don't let the object get too small or too large.
         mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 5.0f));
 
         invalidate();
         return true;
     }
 }
 

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