Asp.net MVC 实现JSONP

JSONP可以帮我们解决跨域访问的问题。JSONP is JSON With Padding. 这里我们将不再解释其原理。我们来看在ASP.NET MVC 3 如何实现。首先我们需要定义一个JsonpResult. 代码像这样, 直接继承自JsonResult, override了ExecuteResult方法

public class JsonpResult : JsonResult
{
    private static readonly string JsonpCallbackName = "callback";
    private static readonly string CallbackApplicationType = "application/json";    /// <summary>
    /// Enables processing of the result of an action method by a custom type that inherits from the <see cref="T:System.Web.Mvc.ActionResult"/> class.
    /// </summary>
    /// <param name="context">The context within which the result is executed.</param>
    /// <exception cref="T:System.ArgumentNullException">The <paramref name="context"/> parameter is null.</exception>
    public override void ExecuteResult(ControllerContext context)
    {
        if (context == null)
        {
            throw new ArgumentNullException("context");
        }
        if ((JsonRequestBehavior == JsonRequestBehavior.DenyGet) &&
              String.Equals(context.HttpContext.Request.HttpMethod, "GET"))
        {
            throw new InvalidOperationException();
        }
        var response = context.HttpContext.Response;
        if (!String.IsNullOrEmpty(ContentType))
            response.ContentType = ContentType;
        else
            response.ContentType = CallbackApplicationType;
        if (ContentEncoding != null)
            response.ContentEncoding = this.ContentEncoding;
        if (Data != null)
        {
            String buffer;
            var request = context.HttpContext.Request;
            var serializer = new JavaScriptSerializer();
            if (request[JsonpCallbackName] != null)
                buffer = String.Format("{0}({1})", request[JsonpCallbackName], serializer.Serialize(Data));
            else
                buffer = serializer.Serialize(Data);
            response.Write(buffer);
        }
    }
}

接着简单定义一个扩展方法:

public static class ContollerExtensions
{
    /// <summary>
    /// Extension methods for the controller to allow jsonp.
    /// </summary>
    /// <param name="controller">The controller.</param>
    /// <param name="data">The data.</param>
    /// <returns></returns>
    public static JsonpResult Jsonp(this Controller controller, object data)
    {
        JsonpResult result = new JsonpResult()
        {
            Data = data,
            JsonRequestBehavior = JsonRequestBehavior.AllowGet
        };        return result;
    }
}

在Controller里使用它, 我们的Controller叫ApiController，其中的Action:

/// <summary>
/// Get some basic information with a JSONP GET request.
/// </summary>
/// <remarks>
///    Sample url:
///    http://localhost:50211/Api/GetInformation?key=test&callback=json123123
/// </remarks>
/// <param name="key">key</param>
/// <returns>JsonpResult</returns>
public JsonpResult GetInformation(string key)
{
    var resp = new Models.CustomObject();
    if (ValidateKey(key))
    {
        resp.Data = "You provided key: " + key;
        resp.Success = true;
    }
    else
    {
        resp.Message = "unauthorized";
    }    return this.Jsonp(resp);
}private bool ValidateKey(string key)
{
    if (!string.IsNullOrEmpty(key))
        return true;
    return false;
}

上面的方法接收一个string的参数，接着我们在前面加一个前缀字符串，最后返回就是Jsonp Result.

传值的Model:

public class CustomObject
{
    public bool Success { get; set; }
    public object Data { get; set; }
    public string Message { get; set; }
}

运行WebSite，访问 http://localhost:50211/Api/GetInformation?callback=myfunction&key=haha

我们可以看到这样的结果:

myfunction({"Success":true,"Data":"You provided key: haha","Message":null})

好的，现在让我们在另一个站点里使用它：

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Index</title>
    <script src="../../Scripts/jquery-1.4.1.min.js" type="text/javascript"></script>
    <script type="text/javascript">
        $(document).ready(function () {
            $('.result').hide();            $('#test').click(function () {
                $('.result').fadeOut('fast');
                $('.result').html('');                $.ajax({
                    url: 'http://localhost:50211/Api/GetInformation',
                    data: { key: $('input[name=key]').val() },
                    type: "GET",
                    dataType: "jsonp",
                    jsonpCallback: "localJsonpCallback"
                });
            });
        });        function localJsonpCallback(json) {
            //do stuff...
            if (json.Success) {
                $('.result').html(json.Data);
            }
            else {
                $('.result').html(json.Message);
            }            $('.result').fadeIn('fast');
        }
    </script>
</head>
<body>
    <div>
        Enter key: <input type="text" name="key" value="some data key, this parameter is optional" />
        <br /><input type="button" value="Test JSONP" id="test" />
        <div class="result">
        </div>
    </div>
</body>
</html>

这里使用的JQuery的Ajax来调用它, 熟悉JQuery的应该能看懂，结果是在button下div显示字符串:

You provided key: some data key, this parameter is optional

在这里，也可以使用getJSON方法。
好了，就这么简单。希望对您Web开发有帮助。

摘自：http://www.cnblogs.com/wintersun/archive/2012/05/25/2518572.html

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