img_minus="tree_images/minus.gif";
img_plus="tree_images/plus.gif";
img_folder_close="tree_images/closedfolder.gif";
img_folder_open="tree_images/openfolder.gif";

function clickOnFolder(obj) {
	var srcIndex=0;
	for(var i=0;srcIndex==0&&i<document.all.length;i++)
		if(obj==document.all[i])srcIndex=i;
	var divElement = document.all[srcIndex+3]; //得到层对象
	var imgElement = document.all[srcIndex+1]; //得到图片对象
	var fimgElement = document.all[srcIndex]; //得到前导图片对象(即它本身)
	if (divElement.style.display == "none"){
		divElement.style.display = "";
		imgElement.src=img_folder_open;
		fimgElement.src=img_minus;
	} else {
		divElement.style.display = "none";
		imgElement.src=img_folder_close;
		fimgElement.src=img_plus;
	}
}