ASP.NET Web API RC版本新特性：Web API的帮助文档制作

InfoQ上有一篇文章是 使用IAPIExplorer列举ASP.NET Web API，文章针对的版本是ASP.NET Web API Beta版本写，IAPIExplorer已经包含在RC版本里了...

InfoQ上有一篇文章是 ​​使用IAPIExplorer列举ASP.NET Web API​​，文章针对的版本是ASP.NET Web API Beta版本写，IAPIExplorer已经包含在RC版本里了，而且发现ASP.NET Web API的HttpConfiguration 的RC版本比Beta版本多了一个属性：

public DefaultServices Services { get; internal set; }

Debug进去可以看到默认有18个服务,IAPIExplorer 就是其中之一：

​​

使用该API可以完成的工作有：

• 产生文档
• 创建机器可读的元数据
• 创建一个测试客户端

微软员工Yao发表了两篇文章（​​ASP.NET Web API: Introducing IApiExplorer/ApiExplorer​​​和​​ASP.NET Web API: Generating a Web API help page using ApiExplorer​​）分别用于展示如何使用API打印Web API列表以及如何创建帮助文档。

所以我们创建帮助文档主要就是参照这篇文章就可以了​​ASP.NET Web API: Generating a Web API help page using ApiExplorer​​；作者在文章里面已经实现了一个IDocumentationProvider，它是通过代码的注释XML文档去生成，这是一个非常好的实现了：

public class XmlCommentDocumentationProvider : IDocumentationProvider  
    { 
        XPathNavigator _documentNavigator; 
        private const string _methodExpression = "/doc/members/member[@name='M:{0}']";
        private static Regex nullableTypeNameRegex = new Regex(@"(.*\.Nullable)" + Regex.Escape("`1[[") + "([^,]*),.*"); 
        public XmlCommentDocumentationProvider(string documentPath) 
        { 
            XPathDocument xpath = new XPathDocument(documentPath); 
            _documentNavigator = xpath.CreateNavigator();
        }  
        public virtual string GetDocumentation(HttpParameterDescriptor parameterDescriptor)  
    { 
        ReflectedHttpParameterDescriptor reflectedParameterDescriptor = parameterDescriptor as ReflectedHttpParameterDescriptor; 
            if (reflectedParameterDescriptor != null) 
            {  
                XPathNavigator memberNode = GetMemberNode(reflectedParameterDescriptor.ActionDescriptor); 
                if (memberNode != null)
                {  
                    string parameterName = reflectedParameterDescriptor.ParameterInfo.Name; 
                    XPathNavigator parameterNode = memberNode.SelectSingleNode(string.Format("param[@name='{0}']", parameterName)); 
                    if (parameterNode != null) 
                    {  
                        return parameterNode.Value.Trim(); 
                    }  
                }  
            } 
            return "No Documentation Found."; 
        }  
        public virtual string GetDocumentation(HttpActionDescriptor actionDescriptor)
        {  
            XPathNavigator memberNode = GetMemberNode(actionDescriptor);
            if (memberNode != null) 
            {  
                XPathNavigator summaryNode = memberNode.SelectSingleNode("summary"); 
                if (summaryNode != null) 
                {  
                    return summaryNode.Value.Trim(); 
                }  
            }  
            return "No Documentation Found."; 
        }  
        private XPathNavigator GetMemberNode(HttpActionDescriptor actionDescriptor) 
        { 
            ReflectedHttpActionDescriptor reflectedActionDescriptor = actionDescriptor as ReflectedHttpActionDescriptor; 
            if (reflectedActionDescriptor != null) 
            {  
                string selectExpression = string.Format(_methodExpression, GetMemberName(reflectedActionDescriptor.MethodInfo)); 
                XPathNavigator node = _documentNavigator.SelectSingleNode(selectExpression); 
                if (node != null) 
                { 
                    return node; 
                }  
            }  
            return null;
        }  
        private static string GetMemberName(MethodInfo method) 
        { 
            string name = string.Format("{0}.{1}", method.DeclaringType.FullName, method.Name);  
            var parameters = method.GetParameters(); 
            if (parameters.Length != 0)  
            {  
                string[] parameterTypeNames = parameters.Select(param => ProcessTypeName(param.ParameterType.FullName)).ToArray(); 
                name += string.Format("({0})", string.Join(",", parameterTypeNames)); 
            } 
            return name; 
        }  
        private static string ProcessTypeName(string typeName)  
        { 
            //handle nullable 
            var result = nullableTypeNameRegex.Match(typeName); 
            if (result.Success) 
            { 
                return string.Format("{0}{{{1}}}", result.Groups[1].Value, result.Groups[2].Value); 
            }  
            return typeName; 
        }  
    }

把XML 文档的位置在Application_Start 中将IDocumentationProvider服务替换为我们的自定义服务。

var config = GlobalConfiguration.Configuration;
config.Services.Replace(typeof(IDocumentationProvider), new XmlCommentDocumentationProvider(HttpContext.Current.Server.MapPath("~/App_Data/MvcApplication2.XML")));有个ApiExplorerSettingsAttribute 可以控制API是否在帮助页面上出现：
/// <summary>
/// DELETE api/values/5
/// </summary>
/// <param name="id"></param>  
[ApiExplorerSettings(IgnoreApi = true)]
public void Delete(int id)
{
}

还可以控制整个ApiController 的文档是否发布出来，只需要通过在类级别应用ApiExplorerSettingsAttribute

[ApiExplorerSettings(IgnoreApi = true)]

public class MySpecialController : ApiController

{

通过IAPIExplorer 这个API我们可以为我们的Web API 做出很棒的文档了，而且这个接口的设计也是可扩展的。可以制作Web页面也可以制作一个HelpController来做，推荐封装成一个HelpController，这样就可以适应WebAPi的Web Host或者是Self Host了。 

​​Part 1: Basic Help Page customizations​​

Changing the help page URI

Providing API documentations

Customizing the view

​​Part 2: Providing custom samples on the Help Page​​

Setting custom sample objects

Setting the samples when the action returns an HttpResponseMessage

​​Part 3: Advanced Help Page customizations​​

Adding additional information to the HelpPageApiModel

Creating new sample display templates

​​Making ASP.NET Web API Help Page work on self-hosted services​​

​​Extending Web API Help Page with information from attributes​​

​​Using curl to POST request into ASP.NET Web Api service​​