AJAX＆QUOT;回调是未定义＆QUOT;错误 [英] ajax "callback is undefined" error

问题描述

目前我正在试图返回一个数据库调用，以填补一个下拉框。当我去循环通过返回的列表，但是，我得到一个回调是不确定的错误。我试过这个code两种方式，也不是工作。

I am currently trying to return a database call to fill a dropdown box. When I go to cycle through the list returned, however, I am getting a "callback is undefined" error. I've tried this code two ways, and neither is working.

我已经试过：

$('#Vehicle_KovId_value').change(function () {
        var kovID = $(this).val();
        var drop2 = $('#Vehicle_BodyStyle_value');
        if (kovID != null && kovID != '') {
            drop2.get(0).options.length = 0;
            drop2.get(0).options[0] = new Option('Please Select One', '-1');
            $.ajax({
                type: "GET",
                url: '/Ajax/Index',
                async: false,
                data: { KovID: kovID },
                contentType: "application/object; charset=utf-8",
                success: function (record) {
                    drop2.get(0).options.length = 0;
                    drop2.get(0).options[0] = new Option("Please Select One", "-1");
                    $.each(function (index, item) {
                    drop2.get(0).options[drop2.get(0).options.length] = new Option(item.Display, item.Value);
                    });
                },
                error: function () {
                    $('#Vehicle_BodyStyle_value').get(0).options.length = 0;
                    $('#Vehicle_BodyStyle_value').get(0).options[0] = new Option("Error!", "-1");
                    alert("Failed to load styles");
                }
            });
        }
    });

我也试过：

$('#Vehicle_KovId_value').change(function () {
        var kovID = $(this).val();
        var drop2 = $('#Vehicle_BodyStyle_value');
        if (kovID != null && kovID != '') {
            drop2.get(0).options.length = 0;
            drop2.get(0).options[0] = new Option('Please Select One', '-1');
            $.ajax({
                type: "GET",
                url: '/Ajax/Index',
                async: false,
                data: { KovID: kovID },
                contentType: "application/object; charset=utf-8",
                success: function (record) {
                    drop2.get(0).options.length = 0;
                    drop2.get(0).options[0] = new Option("Please Select One", "-1");
                    fillBStyles(record);
                    //                    $.each(function (index, item) {
                    //                        drop2.get(0).options[drop2.get(0).options.length] = new Option(item.Display, item.Value);
                    //                    });
                },
                error: function () {
                    $('#Vehicle_BodyStyle_value').get(0).options.length = 0;
                    $('#Vehicle_BodyStyle_value').get(0).options[0] = new Option("Error!", "-1");
                    alert("Failed to load styles");
                }
            });
        }
    });

    function fillBStyles(r) {
        var drop2 = $('#Vehicle_BodyStyle_value');
        $.each(function (index, item) {
            drop2.get(0).options[drop2.get(0).options.length] = new Option(item.Display, item.Value);
        });

    }

其中

这两个给我的错误：

Both of which give me the error:

类型错误：回调未定义

该数据对象被返回，记录，就是我要拉两件从数据库对象的列表。

The data object being returned, record, is a list of database objects that I have to pull two pieces from.

我怎样才能解决这个回调的错误，使我可以用我的数据，我的功能？

How can I fix this "callback" error so that I can use my data in my function?

推荐答案

一个回调将被执行后的predecessor完成它的操作，并返回一个值的函数。在这种情况下，你有两个回调，成功与失败。

A callback is the function to be executed immediately after its predecessor completes it's operation and returns a value. In this case you have two callbacks, success and failure.

函数声明没有内部块允许（的if / else /闭包），这意味着你的回调函数（声明的AJAX闭包）函数（记录）{} 不能放在那里是因为它是在你的如果（kovID = NULL和放大器;！＆安培;！kovID =''）{} 关闭

Function declarations are not allowed inside blocks (if/else/for closures) which means your callback function (which you declare inside your ajax closure) function (record) { } cannot be placed where it is since it is inside your if (kovID != null && kovID != '') { } closure.

幸运的是有一个简单的办法：申报你的成功回调函数外的if语句（把它放在自己在全球范围内）是这样的：

Fortunately there is an easy fix: declare your success callback function outside the if statement (put it by itself in global scope) like this:

function ajaxSuccess(record) {
                drop2.get(0).options.length = 0;
                drop2.get(0).options[0] = new Option("Please Select One", "-1");
                $.each(function (index, item) {
                drop2.get(0).options[drop2.get(0).options.length] = new Option(item.Display, item.Value);
                });
            }
// ...do other javascript stuff

和调用成功，函数是这样的：

and call the success function like this:

$.ajax({
            type: "GET",
            url: '/Ajax/Index',
            async: false,
            data: { KovID: kovID },
            contentType: "application/object; charset=utf-8",
            success: ajaxSuccess
//...blah blah blah

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