c# - 自托管 Web Api C# 与 Windows 窗体错误

Question

我拿了一个示例项目webapi Self Hosting，微软的页面。 webapi正常启动，但是访问地址的时候报如下错误。我正在使用 VS2010 和 Windows 窗体。控制台应用程序正常工作，而 Windows 窗体不工作。

程序代码:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Web.Http.SelfHost;
using System.Web.Http;
using System.Net.Http;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {

        HttpSelfHostServer server;
        HttpSelfHostConfiguration config;

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {

            var config = new HttpSelfHostConfiguration("http://localhost:9090");

            config.Routes.MapHttpRoute(
                "API Default", "api/{controller}/{id}",
                new { id = RouteParameter.Optional });

            using (HttpSelfHostServer server = new HttpSelfHostServer(config))
            {
                server.OpenAsync().Wait();
            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            HttpClient client = new HttpClient();
            client.BaseAddress = new Uri("http://localhost:9090");

            //Console.WriteLine("Products in '{0}':", category);

            string query = string.Format("api/products?category={0}", "testes");

            var resp = client.GetAsync(query).Result;
            //resp.EnsureSuccessStatusCode();

            var products = resp.Content.ReadAsAsync<string>().Result;
            MessageBox.Show(products);
        }
    }
}

Controller :

namespace SelfHost
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Net;
    using System.Web.Http;


    public class ProductsController : ApiController
    {

        public string GetProductsByCategory(string category)
        {
            return (category ?? "Vazio");
        }
    }
}

错误:

This XML file does not appear to have any style information associated with it. The document tree is shown below.
<Error>
<Message>An error has occurred.</Message>
<ExceptionMessage>
Object reference not set to an instance of an object.
</ExceptionMessage>
<ExceptionType>System.NullReferenceException</ExceptionType>
<StackTrace>
at System.Web.Http.SelfHost.HttpSelfHostServer.ProcessRequestContext(ChannelContext channelContext, RequestContext requestContext)
</StackTrace>
</Error>

Answer 1

我看到您的代码有很多错误，但我认为我无法将它们全部包含在评论中。也许如果你修复它们 - 这个异常就会消失。

问题:

1. 在这段代码 server.OpenAsync().Wait(); 之后，您调用 server 上的 Dispose 方法(因为您将所有内容包装在 using 语句中)。这意味着当 OpenAsync 完成时(并且此任务将在服务器运行时完成)- 紧接着您将关闭服务器。

2. 当您在任务上调用 Wait 时，您在主线程上遇到了一堆死锁。查看这篇文章http://blogs.msdn.com/b/pfxteam/archive/2011/01/13/10115163.aspx对此。

这是我尝试重写您的示例以解决这两个问题:

public partial class Form1 : Form
{
    HttpSelfHostServer server;
    HttpSelfHostConfiguration config;

    public Form1()
    {
        InitializeComponent();
    }

    private async void button1_Click(object sender, EventArgs e)
    {
        config = new HttpSelfHostConfiguration("http://localhost:9090");

        config.Routes.MapHttpRoute(
            "API Default", "api/{controller}/{id}",
            new { id = RouteParameter.Optional });

        HttpSelfHostServer server = new HttpSelfHostServer(config);
        await server.OpenAsync();
        // Server is running: you can show something to user like - it is running
        MessageBox.Show("Server is ready!");
    }

    private async void button2_Click(object sender, EventArgs e)
    {
        HttpClient client = new HttpClient();
        client.BaseAddress = new Uri("http://localhost:9090");

        string query = string.Format("api/products?category={0}", "testes");

        var resp = await client.GetAsync(query);

        var products = await resp.Content.ReadAsAsync<string>();
        MessageBox.Show(products);
    }
}