基于ASP.NET AJAX的WebPart开发与部署

            //get the existing ScriptManager if it exists on the page
            _AjaxManager = ScriptManager.GetCurrent(this.Page);

            if (_AjaxManager == null)
            {
                //create new ScriptManager and EnablePartialRendering
                _AjaxManager = new ScriptManager();
                _AjaxManager.EnablePartialRendering = true;

                // Fix problem with postbacks and form actions (DevDiv 55525)
                Page.ClientScript.RegisterStartupScript(typeof(AjaxBaseWebpart), this.ID, "_spOriginalFormAction = document.forms[0].action;", true);

                //tag:"form" att:"onsubmit" val:"return _spFormOnSubmitWrapper()" blocks async postbacks after the first one
                //not calling "_spFormOnSubmitWrapper()" breaks all postbacks
                //returning true all the time, somewhat defeats the purpose of the _spFormOnSubmitWrapper() which is to block repetitive postbacks, but it allows MS AJAX Extensions to work properly
                //its a hack that hopefully has minimal effect
                if (this.Page.Form != null)
                {
                    string formOnSubmitAtt = this.Page.Form.Attributes["onsubmit"];
                    if (!string.IsNullOrEmpty(formOnSubmitAtt) && formOnSubmitAtt == "return _spFormOnSubmitWrapper();")
                    {
                        this.Page.Form.Attributes["onsubmit"] = "_spFormOnSubmitWrapper();";
     &