MVC Controller与ActionResult的返回值

MVC Controller与ActionResult的返回值
Action的要求
• 必须是一个公有方法
• 必须返回ActionResult类型
• 必须是实例方法
• 不能是范型方法
• 没有标注NonActionAttribute
• 不能被重载（overload）

Controller 提供了众多的方法让我们返回各种类型的 ActionResult。

1. View

最常用的一种，用于返回一个 "标准" 页面。

protected internal virtual ViewResult View(string viewName, string masterName, object model)
{
  if (model != null)
  {
    base.ViewData.Model = model;
  }

  return new ViewResult
  {
    ViewName = viewName,
    MasterName = masterName,
    ViewData = base.ViewData,
    TempData = base.TempData
  };
}

public class ViewResult : ViewResultBase
{
  protected override ViewEngineResult FindView(ControllerContext context)
  {
    ViewEngineResult result = ViewEngineCollection.FindView(context, ViewName, MasterName);

    if (result.View != null)
    {
      return result;
    }

    ...
  }
}

这个页面默认是 ViewPage，也可以是我们自己定义的其它模板引擎页面。

MVC 还提供了强类型的 ViewPage<TModel>。

public class User
{
  public string Name { get; set; }
  public int Age { get; set; }
}

public class TestController : Controller
{
  public ActionResult Index()
  {
    ViewData["message"] = "Hello, World!";
    var model = new User { Name = "Tom", Age = 13 };

    return View(model);
  }
}

Index.aspx

<%@ Page Language="C#" Inherits="System.Web.Mvc.ViewPage<Learn.MVC.Controllers.User>" %>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
  <title>Index</title>
</head>
<body>
  Name: <%= Model.Name %>; Age: <%= Model.Age %>
</body>
</html>

在 WebForm 时代，我们就已经习惯了将一个页面分解成多个 UserControl，现在我们依然可以这么做。htmlHelper 专门提供了 RenderPartial 扩展方法，从当前视图目录(Views\xxx)下载入 .ascx 页面。

public static class RenderPartialExtensions
{
  public static void RenderPartial(this HtmlHelper htmlHelper, partialViewName, model, viewData)
  {
    htmlHelper.RenderPartialInternal(partialViewName, viewData, model, ViewEngines.Engines);
  }
}

public class HtmlHelper
{
  internal virtual void RenderPartialInternal(string partialViewName, ViewDataDictionary viewData,
    object model, ViewEngineCollection viewEngineCollection)
  {
    ...

    ViewDataDictionary newViewData = null;

    if (model == null)
    {
      if (viewData == null)
        newViewData = new ViewDataDictionary(ViewData);
      else
        newViewData = new ViewDataDictionary(viewData);
    }
    else
    {
      if (viewData == null)
        newViewData = new ViewDataDictionary(model);
      else
        newViewData = new ViewDataDictionary(viewData) { Model = model };
    }

    ViewContext newViewContext = new ViewContext(ViewContext, ViewContext.View,
      newViewData, ViewContext.TempData);

    IView view = FindPartialView(newViewContext, partialViewName, viewEngineCollection);

    view.Render(newViewContext, ViewContext.HttpContext.Response.Output);
  }

  internal static IView FindPartialView(viewContext, partialViewName, viewEngineCollection)
  {
    ViewEngineResult result = viewEngineCollection.FindPartialView(viewContext, partialViewName);

    if (result.View != null)
    {
      return result.View;
    }

    ...
  }
}

RenderPartialInternal 调用 FindParitialView 从视图引擎中载入 .ascx，同时将当前的环境参数传递给它。也就是说 RenderPartial 只是一种视图级别的行为，并不会再次触发 Controller Action 操作，这点要和 Controller.PartialView() 区别开来。

Index.aspx

<%@ Page Language="C#" Inherits="System.Web.Mvc.ViewPage<Learn.MVC.Controllers.User>" %>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
  <title>Index</title>
</head>
<body>
  Name: <%= Model.Name %>; Age: <%= Model.Age %>
  <br />
  <% Html.RenderPartial("Part"); %>
</body>
</html>

Part.ascx

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<Learn.MVC.Controllers.User>" %>

<%= ViewData["message"] %>
<br />
<%= Model.Name %>

2. Content

Content 用于输出(Response.Write) "静态" 片段。

protected internal virtual ContentResult Content(content, contentType, contentEncoding)
{
  return new ContentResult
  {
    Content = content,
    ContentType = contentType,
    ContentEncoding = contentEncoding
  };
}

public class ContentResult : ActionResult
{
  public string Content { get; set; }

  public override void ExecuteResult(ControllerContext context)
  {
    ...

    HttpResponseBase response = context.HttpContext.Response;

    if (!String.IsNullOrEmpty(ContentType))
    {
      response.ContentType = ContentType;
    }
    if (ContentEncoding != null)
    {
      response.ContentEncoding = ContentEncoding;
    }
    if (Content != null)
    {
      response.Write(Content);
    }
  }
}

看看和 jQuery 的配合使用。

public class TestController : Controller
{
  public ActionResult Index()
  {
    return View();
  }

  public ActionResult Part()
  {
    return Content("<a href=\"http://www.rainsts.net\">Q.yuhen</a>");
  }
}

Index.aspx

<%@ Page Language="C#" Inherits="System.Web.Mvc.ViewPage" %>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
  <title>Index</title>
  <script src="http://www.cnblogs.com/Scripts/jquery-1.3.1.min.js" type="text/javascript"></script>
  <script type="text/javascript">
    $(function()
    {
      $("#div1").load("/test/part");
    });
  </script>
</head>
<body>
  <div id="div1">
  </div>
</body>
</html>

3. PartialView

Controller.PartialView() 和 HtmlHelper.RenderPartial() 的不同之处在于前者是再次执行 ActionInvoke 并返回一个 ActionResult 结果，后者只是使用现有的 ViewContext 显示一个视图片段。而与 Controller.Content() 的区别是 PartialView() 使用视图引擎输出一个 "动态" 的 ascx 结果。

protected internal virtual PartialViewResult PartialView(string viewName, object model)
{
  if (model != null)
  {
    ViewData.Model = model;
  }

  return new PartialViewResult
  {
    ViewName = viewName,
    ViewData = ViewData,
    TempData = TempData
  };
}

public class PartialViewResult : ViewResultBase
{
  protected override ViewEngineResult FindView(ControllerContext context)
  {
    ViewEngineResult result = ViewEngineCollection.FindPartialView(context, ViewName);

    if (result.View != null)
    {
      return result;
    }

    ...
  }
}

和 Content() 一样，我们通常将其和 jQuery 等 Ajax 框架配合使用。

public class TestController : Controller
{
  public ActionResult Index()
  {
    return View();
  }

  public ActionResult Part()
  {
    ViewData["time"] = DateTime.Now;
    var model = new User { Name = "Tom", Age = 13 };

    return PartialView(model);
  }
}

Index.aspx

<%@ Page Language="C#" Inherits="System.Web.Mvc.ViewPage" %>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
  <title>Index</title>
  <script src="http://www.cnblogs.com/Scripts/jquery-1.3.1.min.js" type="text/javascript"></script>
  <script type="text/javascript">
    $(function()
    {
      $("#div1").load("/test/part");
    });
  </script>
</head>
<body>
  <div id="div1">
  </div>
</body>
</html>

Part.ascx

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<Learn.MVC.Controllers.User>" %>

<%= ViewData["time"] %> <br />
<%= Model.Name %>; <%= Model.Age %>

4. Redirect / RedirectToAction / RedirectToRoute

Controller 提供了几种方式，让我们在不同的 Action 之间进行跳转。

public class MvcApplication : System.Web.HttpApplication
{
  public static void RegisterRoutes(RouteCollection routes)
  {
    ...

    routes.MapRoute
    (
      "Test2",
      "Test/T2/{name}/{age}",
      new { controller = "Test", action = "T2", name = "", age = 0 }
    );

    ...
  }
}

方法1:

Redirect() 直接用 Response.Redirect() 完成 url 跳转。

public class TestController : Controller
{
  public ActionResult Index()
  {
    return Redirect("/Test/T2/Tom/23");
  }

  public ActionResult T2(User user)
  {
    return Content(user.Name);
  }
}

相关细节：

protected internal virtual RedirectResult Redirect(string url)
{
  ...
  return new RedirectResult(url);
}

public class RedirectResult : ActionResult
{
  public override void ExecuteResult(ControllerContext context)
  {
    ...

    string destinationUrl = UrlHelper.Content(Url, context.HttpContext);
    context.HttpContext.Response.Redirect(destinationUrl, false /* endResponse */);
  }
}

方法2:

RedirectToAction() 直接使用 Action Name 进行跳转。

public class TestController : Controller
{
  public ActionResult Index()
  {
    return RedirectToAction("T2", new { name = "Tom", age = 23 });
  }

  public ActionResult T2(User user)
  {
    return Content(user.Name);
  }
}

如果目标 Action 不在当前 Controller 类，则可以指定目标 Controller Name。

return RedirectToAction("T2", new { controller="Test2", name = "Tom", age = 23 });

相关细节：

protected internal virtual RedirectToRouteResult RedirectToAction(string actionName,
  string controllerName, RouteValueDictionary routeValues)
{
  RouteValueDictionary mergedRouteValues;

  if (RouteData == null)
  {
    mergedRouteValues = RouteValuesHelpers.MergeRouteValues(actionName,
      controllerName, null, routeValues, true /* includeImplicitMvcValues */);
  }
  else
  {
    mergedRouteValues = RouteValuesHelpers.MergeRouteValues(actionName,
      controllerName, RouteData.Values, routeValues, true /* includeImplicitMvcValues */);
  }

  return new RedirectToRouteResult(mergedRouteValues);
}

public class RedirectToRouteResult : ActionResult
{
  public override void ExecuteResult(ControllerContext context)
  {
    ...

    string destinationUrl = UrlHelper.GenerateUrl(RouteName, null /* actionName */,
      null /* controllerName */, RouteValues, Routes, context.RequestContext,
      false /* includeImplicitMvcValues */);

    ...
    context.HttpContext.Response.Redirect(destinationUrl, false /* endResponse */);
  }
}

可以看到 RedirectToRouteResult.ExecuteResult 中使用 Route 相关信息拼接成目标 Url 后进行跳转。

方法3:

RedirectToRoute() 则是直接用 MapRoute 时定义的 Route Name 进行跳转。

public class TestController : Controller
{
  public ActionResult Index()
  {
    return RedirectToRoute("Test2", new { name = "Tom", age = 23 });
  }
}

相关细节：

protected internal virtual RedirectToRouteResult RedirectToRoute(string routeName, RouteValueDictionary routeValues)
{
  return new RedirectToRouteResult(routeName, RouteValuesHelpers.GetRouteValues(routeValues));
}

执行过程和 RedirectToAction() 相同。

5. Json

Json() 在编写 Ajax 时非常有用，可以将 Entity 等对象序列化成 JSON 格式供 Javascript 使用。

public class TestController : Controller
{
  public ActionResult Index()
  {
    return View();
  }

  public ActionResult GetUser(string name)
  {
    var user = new User { Name = name, Age = 23 };
    return Json(user);
  }
}

Index.aspx

<%@ Page Language="C#" Inherits="System.Web.Mvc.ViewPage" %>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
  <title>Index</title>
  <script src="http://www.cnblogs.com/Scripts/jquery-1.3.1.min.js" type="text/javascript"></script>
  <script type="text/javascript">
    $(function()
    {
      $("#btnTest").click(function()
      {
        $.getJSON
        (
          "/Test/GetUser",
          { name: "Tom" },
          function(json)
          {
            alert(json.Name + ";" + json.Age);
          }
        );
      });
    });
  </script>
</head>
<body>
  <input type="button" id="btnTest" value="Test" />
</body>
</html>

很好用，不是吗？看看相关细节。

protected internal virtual JsonResult Json(object data, string contentType, Encoding contentEncoding)
{
  return new JsonResult
  {
    Data = data,
    ContentType = contentType,
    ContentEncoding = contentEncoding
  };
}

public class JsonResult : ActionResult
{
  public override void ExecuteResult(ControllerContext context)
  {
    ...

    if (Data != null)
    {
      JavaScriptSerializer serializer = new JavaScriptSerializer();
      response.Write(serializer.Serialize(Data));
    }
  }
}

使用 System.Web.Script.Serialization.JavaScriptSerializer 完成 JSON 序列化操作，也就是说我们还可以用 ScriptIgnoreAttribute 排除某些属性。

6. Javascript

某些时候，我们需要根据一些逻辑判断来载入执行不同的 Javascript 代码。

public class TestController : Controller
{
  public ActionResult Index()
  {
    return View();
  }

  public ActionResult GetJs(int id)
  {
    switch (id)
    {
      case 1:
        return JavaScript("alert('Hello, C#!');");
      case 2:
        return JavaScript("alert('Hello, MVC!');");
      default:
        return null;
    }
  }
}

Index.aspx

<%@ Page Language="C#" Inherits="System.Web.Mvc.ViewPage" %>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
  <title>Index</title>
  <script src="http://www.cnblogs.com/Scripts/jquery-1.3.1.min.js" type="text/javascript"></script>
  <script type="text/javascript">
    $(function()
    {
      $("#btnTest").click(function()
      {
        var id = $("#txtId").val();
        $.getScript("/Test/GetJs/" + id);
      });
    });
  </script>
</head>
<body>
  <input type="text" id="txtId" value="1" />
  <input type="button" id="btnTest" value="Test" />
</body>
</html>

只是这种做法，似乎将 View 和 Controller 的耦合加大了…… 还不如直接用 Javascript 来处理这些。

protected internal virtual JavaScriptResult JavaScript(string script)
{
  return new JavaScriptResult { Script = script };
}

public class JavaScriptResult : ActionResult
{
  public override void ExecuteResult(ControllerContext context)
  {
    ...

    HttpResponseBase response = context.HttpContext.Response;
    response.ContentType = "application/x-javascript";

    if (Script != null)
    {
      response.Write(Script);
    }
  }
}

7. File (Download / Upload)

File() 提供了 Download 功能。

public class TestController : Controller
{
  public ActionResult Index()
  {
    return View();
  }

  public ActionResult Download(int id)
  {
    var filename = String.Format("~/Content/Download/{0}.rar", id);
    var fileDownloadName = String.Format("{0}.rar", id);

    return File(filename, "application/octet-stream", fileDownloadName);
  }
}

当我们在浏览器请求 "/Test/Download/1" 是就会打开下载窗口，同时给出了保存文件名。

protected internal virtual FileContentResult File(byte[] fileContents, contentType, fileDownloadName)
{
  return new FileContentResult(fileContents, contentType) { FileDownloadName = fileDownloadName };
}

public abstract class FileResult : ActionResult
{
  public override void ExecuteResult(ControllerContext context)
  {
    ...
    HttpResponseBase response = context.HttpContext.Response;
    response.ContentType = ContentType;
    ...
    WriteFile(response);
  }

  protected abstract void WriteFile(HttpResponseBase response);
}

public class FileContentResult : FileResult
{
  protected override void WriteFile(HttpResponseBase response)
  {
    response.OutputStream.Write(FileContents, 0, FileContents.Length);
  }
}

文件上传是另一个常用的 Web 应用。

public class TestController : Controller
{
  public ActionResult Index()
  {
    return View();
  }

  public ActionResult Upload(HttpPostedFileBase file)
  {
    var filename = Server.MapPath("~/Content/Upload/" + Path.GetFileName(file.FileName));

    file.SaveAs(filename);
    return null;
  }
}

Index.aspx

<%@ Page Language="C#" Inherits="System.Web.Mvc.ViewPage" %>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
  <title>Index</title>
</head>
<body>
  <form action="/Test/Upload" enctype="multipart/form-data" method="post">
    <input type="file" name="file" />
    <input type="submit" name="upload" />
  </form>
</body>
</html>

MVC 提供了一个 HttpPostedFileBaseModelBinder 将 Request.Files 的信息直接映射给 Action 同名参数。

public class HttpPostedFileBaseModelBinder : IModelBinder
{
  public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
  {
    ...

    HttpPostedFileBase theFile = controllerContext.HttpContext.Request.Files[bindingContext.ModelName];

    // case 1: there was no <input type="file" ... /> element in the post
    if (theFile == null)
    {
      return null;
    }

    // case 2: there was an <input type="file" ... /> element in the post, but it was left blank
    if (theFile.ContentLength == 0 && String.IsNullOrEmpty(theFile.FileName))
    {
      return null;
    }

    // case 3: the file was posted
    return theFile;
  }
}

看看一次上传多个文件的演示。

public class TestController : Controller
{
  public ActionResult Index()
  {
    return View();
  }

  public ActionResult Upload(HttpPostedFileBase file1, HttpPostedFileBase file2)
  {
    var html = String.Format("{0}:{1}<br />{2}:{3}",
      file1.FileName, file1.InputStream.Length,
      file2.FileName, file2.InputStream.Length);

    return Content(html);
  }
}

Index.aspx

<%@ Page Language="C#" Inherits="System.Web.Mvc.ViewPage" %>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
  <title>Index</title>
</head>
<body>
  <form action="/Test/Upload" enctype="multipart/form-data" method="post">
    <input type="file" name="file1" />
    <input type="file" name="file2" />
    <input type="submit" name="upload" />
  </form>
</body>
</html>

我们上边所看到的Action都是return View();我们可以看作这个返回值用于解析一个aspx文件。而它的返回类型是ActionResult如
```
 public ActionResult Index()
 {
 return View();
 }
```
除了View（）之外那我们这里还能用于返回什么值呢？

一、ascx页面

场景：要返回代码片断，比如Ajax返回一个子页

我们先新建一个Action
```
 public ActionResult Ascx()
 {
 return PartialView();
 }
```
我们下面再建一个View，仍然是在Action中点右键，AddView。

注意图中勾选。

于是新建了一个ascx页，我们将之少做改写一下
```
<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl" %>
<div>
得到一个DIV
</div>
```
运行，得到页面

二、返回文本

除了上述情况，有时我们还会仅返回一段文本。

此时我们可以使用以下Action形式：
```
 public ActionResult Text(){
 return Content("这是一段文本");
 }
```
三、返回Json

有时我们在调用Ajax时还会要求返回对象为Json序列化的结果，如：
```
 public ActionResult ShowJson()
 {
 var m = new EiceIndexModel
 {
 Name = "邹健",
 Sex = true
 };
 return Json(m);
 }
```
返回文本：
```
{"Name":"邹健","Sex":true}
```
四、输出JS文件

大多时候js文件都是静态的，但有时js文件可能也要动态生成这时我们可以这样输出
```
 public ActionResult Js()
 {
 return JavaScript("var x=0;");
 }
```
我们访问之，得到一个正常页面但其Content-Type：application/x-javascript; charset=utf-8

五、页面跳转

1.跳转到Url
```
 public ActionResult rdurl()
 {
 return Redirect("http://www.baidu.com");
 }
```
2.跳转到Action
```
 public ActionResult rdaction()
 {
 return RedirectToAction("Index","Eice");
 }
```
3.跳转到Routing规则
```
 public ActionResult rdrouting()
 {
 return RedirectToRoute("Default",//Route名
 new{
 Controller = "Eice",
 Action = "Index"
 });
 }
```
六、显示文件
```
 public ActionResult fn()
 {
 return File(
 "/Content/site.css"//文件路径
 , "text/css"//文件类型
 );
 }
```
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原文地址：https://www.cnblogs.com/stalwart/p/1765172.html

MVC Controller与ActionResult的返回值

一、ascx页面

二、返回文本

三、返回Json

四、输出JS文件

五、页面跳转

六、显示文件