I solved the problem as follows. It does not change seek bar value if touched outside the thumb image.
holder.vertical_seekBar.setOnTouchListener(new OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
if(event.getAction() == MotionEvent.ACTION_MOVE ||
event.getAction() == MotionEvent.ACTION_UP ||
event.getAction() == MotionEvent.ACTION_DOWN){
Rect seekBarThumbRect = holder.vertical_seekBar.getSeekBarThumb().getBounds();
int seekBarHeight = holder.vertical_seekBar.getHeight();
if(seekBarThumbRect.left - (seekBarThumbRect.right - seekBarThumbRect.left) / 2 < (Math.abs(seekBarHeight - event.getY())) &&
seekBarThumbRect.right + (seekBarThumbRect.right - seekBarThumbRect.left) / 2 > (Math.abs(seekBarHeight - event.getY())) &&
seekBarThumbRect.top < event.getX() &&
seekBarThumbRect.bottom > event.getX())
return false;
}
return true;
}
});