当 AutoPostBack="True" 时，DropDownList 未触发 onbeforeunload

Question

我已经使用这些页面上描述的技术实现了“未保存的更改”警告：

Client/JS Framework for "Unsaved Data" Protection?

http://kenbrowning.blogspot.com/2009/01/using-jquery-to-standardize.html

这很好用，除了页面上的 DropDownList。它执行 AutoPostBack，我希望 onbeforeunload 触发，因为未保存的更改将丢失，但它不起作用。它应该引发 onbeforeunload 事件吗？我能以某种方式让它引发事件吗？

编辑： DropDownList 位于 UpdatePanel 内，因此这意味着它不会卸载页面，这就是未触发 onbeforeunload 的原因。有什么办法可以以编程方式触发事件吗？还是我必须推出自己的模仿确认对话框？

编辑2 我现在有一个解决方案，可以将对话框添加到来自 UpdatePanel 的异步回发中。我已经编辑了原始脚本，添加了对 setConfirmAsyncPostBack() 的调用，如我的解决方案中所述。

这是我的 javascript：

/****Scripts to warn user of unsaved changes****/

//https://stackoverflow.com/questions/140460
//http://jonstjohn.com/node/23

//Activates the confirm message onbeforeunload.
function setConfirmUnload(on) {

    setConfirmAsyncPostBack();

    if (on) {
        removeCheckFromNoWarnClasses();
        fixIEonBeforeUnload();
        window.onbeforeunload = unloadMessage
        return;
    }

    window.onbeforeunload = null
}

function unloadMessage() {

    return 'You have unsaved changes.';
}

//Moves javascript from href to onclick to prevent IE raising onbeforeunload unecessarily
//http://kenbrowning.blogspot.com/2009/01/using-jquery-to-standardize.html
function fixIEonBeforeUnload() {

    if (!$.browser.msie)
        return;
    $('a').filter(function() {
        return (/^javascript\:/i).test($(this).attr('href'));
    }).each(function() {
        var hrefscript = $(this).attr('href');
        hrefscript = hrefscript.substr(11);
        $(this).data('hrefscript', hrefscript);
    }).click(function() {
        var hrefscript = $(this).data('hrefscript');
        eval(hrefscript);
        return false;
    }).attr('href', '#');
}

//Removes warnings from Save buttons, links, etc, that have been can be given "no-warn" or "no-warn-validate" css class
//"no-warn-validate" inputs/links will only remove warning after successful validation
//use the no-warn-validate class on buttons/links that cause validation. 
//use the no-warn class on controls that have CausesValidation=false (e.g. a "Save as Draft" button).
function removeCheckFromNoWarnClasses() {

    $('.no-warn-validate').click(function() {
        if (Page_ClientValidate == null || Page_ClientValidate()) {
            setConfirmUnload(false);
        }
    });

    $('.no-warn').click(function() {
        setConfirmUnload(false);
    });
}

//Adds client side events to all input controls to switch on confirmation onbeforeunload
function enableUnsavedChangesWarning() {

    $(':input').one('change', function() {
        window.onbeforeunload = function() {
            return 'You have unsaved changes.';
        }
    });

    removeCheckFromNoWarnClasses();
}

在我的 ASP.NET 页面中，当用户进行更改时：

    if (changed)
    {
        ...
        //Confirm unload if there are unsaved changes. 
        //NB we also have to call fixIEonBeforeUnload() to fix links, done in in page load to include links that are rendered during callbacks
        ScriptManager.RegisterStartupScript(Page, GetType(), "unsavedchanges", "setConfirmUnload(true);", true);
    }
    else
        ...

Answer 1

另见How to prevent AutoPostBack when DropDownlist is selected using jQuery

//http://msdn.microsoft.com/en-us/magazine/cc163413.aspx
//https://stackoverflow.com/questions/2424327/prevent-asp-net-dopostback-from-jquery-submit-within-updatepanel
//Adds an event handler to confirm unsaved changes when an asynchronous postback is initialised by an UpdatePanel
function setConfirmAsyncPostBack() {

    if (typeof (Sys.WebForms) === "undefined" || typeof (Sys.WebForms.PageRequestManager) === "undefined")
        return;

    var prm = Sys.WebForms.PageRequestManager.getInstance();
    prm.add_initializeRequest(confirmAsyncPostBack);
}

//An event handler for asynchronous postbacks that confirms unsaved changes, cancelling the postback if they are not confirmed
//Adds the confirmation to elements that have a css class of "warn"
function confirmAsyncPostBack(sender, args) {
    if (window.onbeforeunload != null && args.get_postBackElement().className == "warn" && !unloadConfirmed())
        args.set_cancel(true);
}

//Displays a confirmation dialog that imitates the dialog displayed by onbeforeunload
function unloadConfirmed() {

    var confirmed = confirm("Are you sure you want to navigate away from this page?\n\n" + unloadMessage() + "\n\nPress OK to continue or Cancel to stay on the current page.");
    if (confirmed)
        window.onbeforeunload = null;
    return confirmed;
}