Asp.Net Core 2.0 之旅---@Html.Action

想必只要 接触了 net core的小伙伴们 已经发现 @html.Action()方法 官方已经不提供支持了，转而使用
ViewComponents替代了，同时也增加了TagHelper。但是 如果想用以前的@Html.Action()方法，我们其实可以自己动手去实现它。

下面就开始 实现之旅吧！

1、创建 静态类 HtmlHelperViewExtensions，其命名空间为  Microsoft.AspNetCore.Mvc.Rendering。这样我们直接用@Html直接可以 使用Action方法了。

namespace Microsoft.AspNetCore.Mvc.Rendering
{
public static class HtmlHelperViewExtensions
{
public static IHtmlContent Action(this IHtmlHelper helper, string action, object parameters = null)
{
var controller = (string)helper.ViewContext.RouteData.Values["controller"];

return Action(helper, action, controller, parameters);
}

public static IHtmlContent Action(this IHtmlHelper helper, string action, string controller, object parameters = null)
{
var area = (string)helper.ViewContext.RouteData.Values["area"];

return Action(helper, action, controller, area, parameters);
}

public static IHtmlContent Action(this IHtmlHelper helper, string action, string controller, string area, object parameters = null)
{
if (action == null)
throw new ArgumentNullException("action");

if (controller == null)
throw new ArgumentNullException("controller");

var task = RenderActionAsync(helper, action, controller, area, parameters);

return task.Result;
}

private static async Task<IHtmlContent> RenderActionAsync(this IHtmlHelper helper, string action, string controller, string area, object parameters = null)
{
// fetching required services for invocation
var serviceProvider = helper.ViewContext.HttpContext.RequestServices;
var actionContextAccessor = helper.ViewContext.HttpContext.RequestServices.GetRequiredService<IActionContextAccessor>();
var httpContextAccessor = helper.ViewContext.HttpContext.RequestServices.GetRequiredService<IHttpContextAccessor>();
var actionSelector = serviceProvider.GetRequiredService<IActionSelector>();

// creating new action invocation context
var routeData = new RouteData();
foreach (var router in helper.ViewContext.RouteData.Routers)
{
routeData.PushState(router, null, null);
}
routeData.PushState(null, new RouteValueDictionary(new { controller = controller, action = action, area = area }), null);
routeData.PushState(null, new RouteValueDictionary(parameters ?? new { }), null);

//get the actiondescriptor
RouteContext routeContext = new RouteContext(helper.ViewContext.HttpContext) { RouteData = routeData };
var candidates = actionSelector.SelectCandidates(routeContext);
var actionDescriptor = actionSelector.SelectBestCandidate(routeContext, candidates);

var originalActionContext = actionContextAccessor.ActionContext;
var originalhttpContext = httpContextAccessor.HttpContext;
try
{
var newHttpContext = serviceProvider.GetRequiredService<IHttpContextFactory>().Create(helper.ViewContext.HttpContext.Features);
if (newHttpContext.Items.ContainsKey(typeof(IUrlHelper)))
{
newHttpContext.Items.Remove(typeof(IUrlHelper));
}
newHttpContext.Response.Body = new MemoryStream();
var actionContext = new ActionContext(newHttpContext, routeData, actionDescriptor);
actionContextAccessor.ActionContext = actionContext;
var invoker = serviceProvider.GetRequiredService<IActionInvokerFactory>().CreateInvoker(actionContext);
await invoker.InvokeAsync();
newHttpContext.Response.Body.Position = 0;
using (var reader = new StreamReader(newHttpContext.Response.Body))
{
return new HtmlString(reader.ReadToEnd());
}
}
catch (Exception ex)
{
return new HtmlString(ex.Message);
}
finally
{
actionContextAccessor.ActionContext = originalActionContext;
httpContextAccessor.HttpContext = originalhttpContext;
if (helper.ViewContext.HttpContext.Items.ContainsKey(typeof(IUrlHelper)))
{
helper.ViewContext.HttpContext.Items.Remove(typeof(IUrlHelper));
}
}
}
}
}

2、 在Startup中的 ConfigureServices 方法添加：

services.AddSingleton<IHttpContextAccessor, HttpContextAccessor();

services.AddSingleton<IActionContextAccessor, ActionContextAccessor>();

（备注：因为net core 默认不将IHttpContextAccessor，IActionContextAccessor 依赖注入，所以需要手动进行依赖注入）

3、在页面中，我们就可以直接用 @Html.Action()方法 直接请求 控制器的方法了。          

4、小结：如今微软官方已经提供了 新的 TagHelper、View components 来替代之前的写法。这个教程只适用于对视图层不想做更变的小伙伴使用。如果 是新项目的，还是建议使用 View components!