asp.net - asp.net-ajax EndRequest 处理程序未触发

Question

我已经使用 aspnet ajax 来显示服务器请求的进度图像。代码：

Sys.WebForms.PageRequestManager.getInstance().add_beginRequest(BeginRequestHandler);
        Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequestHandler);
        function BeginRequestHandler(sender, args) {
            //             alert('B');
            var elem = args.get_postBackElement();
            ActivateAlertDiv('visible', 'AlertDiv', elem.value + ' processing...');
        }
        function EndRequestHandler(sender, args) {
            ActivateAlertDiv('hidden', 'AlertDiv', '');
        }
        function ActivateAlertDiv(visstring, elem, msg) {
            var adiv = $get(elem);
            adiv.style.visibility = visstring;
            //                    adiv.innerHTML = msg;
        }

BeginRequestHandler 被调用并且进度图像可见但 EndRequestHandler 未被调用。由于此进度图像连续运行。