public SlideModel set(int location, SlideModel object) {
    SlideModel slide = mSlides.get(location);
    if (null != object) {
      int removeSize = 0;
      int addSize = object.getSlideSize();
      if (null != slide) {
        removeSize = slide.getSlideSize();
      }
      if (addSize > removeSize) {
        checkMessageSize(addSize - removeSize);
        increaseMessageSize(addSize - removeSize);
      } else {
        decreaseMessageSize(removeSize - addSize);
      }
    }

    slide = mSlides.set(location, object);
    if (slide != null) {
      slide.unregisterAllModelChangedObservers();
    }

    if (object != null) {
      object.registerModelChangedObserver(this);
      for (IModelChangedObserver observer : mModelChangedObservers) {
        object.registerModelChangedObserver(observer);
      }
    }

    notifyModelChanged(true);
    return slide;
  }
 public SlideModel remove(int location) {
   SlideModel slide = mSlides.remove(location);
   if (slide != null) {
     decreaseMessageSize(slide.getSlideSize());
     slide.unregisterAllModelChangedObservers();
     notifyModelChanged(true);
   }
   return slide;
 }
 public boolean remove(Object object) {
   if ((object != null) && mSlides.remove(object)) {
     SlideModel slide = (SlideModel) object;
     decreaseMessageSize(slide.getSlideSize());
     slide.unregisterAllModelChangedObservers();
     notifyModelChanged(true);
     return true;
   }
   return false;
 }