是treeview兑现单选

        function getTargetElement(evt) {
            var elem
            if (evt.target) {
                elem = (evt.target.nodeType == 3) ? evt.target.parentNode : evt.target
            }
            else {
                elem = evt.srcElement
            }
            return elem
        }
        var lastC = null;
        function OnClientTreeNodeChecked(evt) {
            evt = (evt) ? evt : ((window.event) ? window.event : " ");
            if (evt == " ") {
                return;
            }
            var obj = getTargetElement(evt);
            var hasTreeNode = false;
            if (obj.tagName) {
                if (obj.tagName == "INPUT" && obj.type == "checkbox") {
                    if (lastC) lastC.checked = false
                    lastC = obj;
                    obj.checked = true;
                }
            }
        }

      TreeView1.Attributes.Add("onclick ", "OnClientTreeNodeChecked(event)");