jquery ajax 发送到 MVC 控制器时不断收到 400（错误请求）

我的 ajax 调用看起来像这样

$.ajax({ //actually approve or reject the promotion
                url: url,
                type: "POST",
                data: '{'+data.PromotionId+','+data.UserId+','+data.ReasonText+'}',
                dataType: "json",
                //contentType: "application/json; charset=utf-8",
                success: function (data) {
                    if (indicator == 'A') {
                        alert('Promotion approved successfully!');
                    }
                    else {
                        alert('Promotion rejected successfully.');
                    }

                    var homelink = '<%: Url.Action("Index","Home") %>';
                    window.location.href = (homelink);


                    returndata = data;
                },
                error: function (xhRequest, ErrorText, thrownError) {
                    alert("Failed to process promotion correctly, please try again");
                    console.log('xhRequest: ' + xhRequest + "\n");
                    console.log('ErrorText: ' + ErrorText + "\n");
                    console.log('thrownError: ' + thrownError + "\n");
                }
            });

我的 MVC 控制器如下所示：

 [HttpPost]
    public HttpResponseMessage ApprovePromotion(PromotionDecision decision)
    {
        if (ModelState.IsValid && decision != null)
        {
            bool status = PromotionBo.ApprovePromotion(decision);
            if (status == true)
                return new HttpResponseMessage(HttpStatusCode.OK);
        }
        return new HttpResponseMessage(HttpStatusCode.BadRequest);
    }

我原以为这两个方法的语法都是正确的，但是每次我进行 ajax 调用时，我都会收到 400 响应。我做错了什么？

您正在向服务器发送一个完全损坏且无效的 JSON 字符串。控制器操作拒绝它是正常的。除此之外，您还发表了评论contentType参数指定您要发送 JSON 请求。

所以这是执行请求的正确方法：

$.ajax({ //actually approve or reject the promotion
    url: url,
    type: "POST",
    data: JSON.stringify({ 
        // Those property names must match the property names of your PromotionDecision  view model
        promotionId: data.PromotionId, 
        userId: data.UserId, 
        reasonText: data.ReasonText
    }),
    contentType: "application/json; charset=utf-8",
    success: function (data) {
        if (indicator == 'A') {
            alert('Promotion approved successfully!');
        }
        else {
            alert('Promotion rejected successfully.');
        }

        var homelink = '<%: Url.Action("Index","Home") %>';
        window.location.href = (homelink);

        returndata = data;
    },
    error: function (xhRequest, ErrorText, thrownError) {
        alert("Failed to process promotion correctly, please try again");
        console.log('xhRequest: ' + xhRequest + "\n");
        console.log('ErrorText: ' + ErrorText + "\n");
        console.log('thrownError: ' + thrownError + "\n");
    }
});

请注意我如何使用JSON.stringify现代浏览器原生内置的方法，可确保发送到服务器的 JSON 正确并且所有值都正确编码。如果您需要支持石器时代的浏览器，您可以包括json2.js https://github.com/douglascrockford/JSON-js脚本到您的页面，它将定义JSON.stringify方法。

重要说明：绝对不会像代码中一样使用字符串连接构建 JSON 字符串。

或者，如果您不想发送 JSON 请求，您可以发送标准application/x-www-form-urlencoded要求：

$.ajax({ //actually approve or reject the promotion
    url: url,
    type: "POST",
    data: { 
        promotionId: data.PromotionId, 
        userId: data.UserId, 
        reasonText: data.ReasonText
    },
    success: function (data) {
        if (indicator == 'A') {
            alert('Promotion approved successfully!');
        }
        else {
            alert('Promotion rejected successfully.');
        }

        var homelink = '<%: Url.Action("Index","Home") %>';
        window.location.href = (homelink);

        returndata = data;
    },
    error: function (xhRequest, ErrorText, thrownError) {
        alert("Failed to process promotion correctly, please try again");
        console.log('xhRequest: ' + xhRequest + "\n");
        console.log('ErrorText: ' + ErrorText + "\n");
        console.log('thrownError: ' + thrownError + "\n");
    }
});

这应该以相同的方式工作，并且控制器操作应该能够正确绑定模型。

备注：我注意到您在成功回调中使用了以下行：returndata = data;。这让我相信您正在以某种方式尝试在成功回调之外使用异步 AJAX 请求的结果，这是不可能的。我不知道你用这个做什么returndata变量，但我觉得这是错误的。