使用JQuery将div设置为100％高度的问题

Hi I'm using Jquery to animate a div from a set height to 100% and back to a set height again. This is used to show/hide text from a wordpress post that is longer then the set height (overflow is hidden). I'm not able to animate the div from the set height to 100% -- instead the div jumps to 100% of the height. It does animate back to it's set size smoothly. I can't fix a height for it to animate to because the posts will always have a different height according to how much has been written.Hi I'm using Jquery to animate a div from a set