blocks|key|1627008|text|这并不能解释为什么您的参数为空，但您可以直接深入研究该请求。不过，这可能不是最"MVC“的方式。在你的方法体中尝试这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1627009|var+upload+=+Request.Files["postedFile"]
if+(upload.ContentLength+>+0)
{
++//+Do+whatever
}|code-block|syntax|javascript|1627010|为了更加"MVC“，您可以将该代码从控制器中提取到IModelBinder实现中，并使用自定义对象作为您的方法的参数。此Scott+Hanselman+blog+post显示了实现自定义ModelBinder的步骤。|offset|length|1627011|entityMap|0|LINK|mutability|MUTABLE|url|http://www.hanselman.com/blog/IPrincipalUserModelBinderInASPNETMVCForEasierTesting.aspx^0|0|0|1O|P|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

This doesn't answer why your parameter is null, but you can dig into the request directly. This might not be the most "MVC" way of doing this though. try this in your method body:

<pre><code>var upload = Request.Files["postedFile"]
if (upload.ContentLength &gt; 0)
{
 // Do whatever
}
</code></pre>

To be more "MVC, "You could pull that code out of your controller into an IModelBinder implementation and using a custom object as a parameter to your method. This <a href="http://www.hanselman.com/blog/IPrincipalUserModelBinderInASPNETMVCForEasierTesting.aspx" rel="noreferrer">Scott Hanselman blog post</a> shows the steps to implement a custom ModelBinder.

blocks|key|1412343|text|我对<%25=+Html.BeginForm+...%25>也有一些奇怪的地方。所以，我使用了using。同样，在控制器端，我只是从request对象中获取上传的文件。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1412344|尝尝这个。它是有效的：|1412345|<%25+using+(Html.BeginForm("Post",+"Home",+FormMethod.Post,+new+{enctype+=+"multipart/form-data"}))
+++{%25>

++++<input+type="file"+id="postedFile"+name="PostedFile"+/>
++++<input+type="submit"+/>

<%25
}|code-block|syntax|javascript|1412346|%25>|1412347|[AcceptVerbs(HttpVerbs.Post)]
++++public+ActionResult+Post(FormCollection+form)
++++{
++++++HttpPostedFileBase+postedFile+=+++Request.Files["PostedFile"];
++++++++return+RedirectToAction("Index");
++++}|1412348|entityMap^0|2|O|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|V|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|W|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|X|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|Y|8|@]|D|@]|E|$K|L]]|$1|Q|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|R|$]]

I also get some quirks with <code>&lt;%= Html.BeginForm ...%&gt;</code>. So, I use the using. Again, on the Controller side, I just grab my uploaded files form the request object.

Try this. It works:

<pre><code>&lt;% using (Html.BeginForm("Post", "Home", FormMethod.Post, new {enctype = "multipart/form-data"}))
 {%&gt;

 &lt;input type="file" id="postedFile" name="PostedFile" /&gt;
 &lt;input type="submit" /&gt;

&lt;%
}
</code></pre>

%>

<pre><code>[AcceptVerbs(HttpVerbs.Post)]
 public ActionResult Post(FormCollection form)
 {
 HttpPostedFileBase postedFile = Request.Files["PostedFile"];
 return RedirectToAction("Index");
 }
</code></pre>

blocks|key|1627097|text|您使用的是哪个版本的MVC？现在，对于RC候选人，我尝试使用HttpPostedFile，但得到了一个“没有空白构造函数错误”。我不得不使用HttpPostedFileBase。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1627098|但更重要的是，您正在运行的MVC的版本，根据版本的不同，检索发布的文件的方式也会有所不同。|1627099|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Which version of MVC are you using?
Right now with the RC candidate I tried using HttpPostedFile and I got an "does not have a blank constructor error." I had to use HttpPostedFileBase.

More importantly though, is the version of MVC you're running on, depending on the version, how your retrieve a posted file will be different.

blocks|key|1412407|text|使用HttpPostedFileBase+(而不是HttpPostedFile)并将参数命名为与表单中完全相同的名称。例如：如果你有|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1412408|<input+type="file"+id="file1"+name="file1"+/>|code-block|syntax|javascript|1412409|你必须有方法的头部：|1412410|public+ActionResult+About(HttpPostedFileBase+file1)|1412411|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Use HttpPostedFileBase (not HttpPostedFile) and also name the parameter exactly as in the form. eg. if you have 

<pre><code>&lt;input type="file" id="file1" name="file1" /&gt;
</code></pre>

you have to have the method head: 

<pre><code>public ActionResult About(HttpPostedFileBase file1)
</code></pre>

blocks|key|1412441|text|我也有同样的问题：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1412442|您必须为input元素定义一个名称和id：|1412443|<input+type="file"+name="postedFile"+id="postedFileId"++/>+|code-block|syntax|javascript|1412444|诚挚的问候|1412445|斯特凡|1412446|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I had the same problem:

You have to define a name AND id for the input element:

<pre><code>&lt;input type="file" name="postedFile" id="postedFileId" /&gt; 
</code></pre>

Best regards

Stefan

blocks|key|1627197|text|您应该删除enctype属性末尾的空格：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1627198|new+{enctype="multipart/form-data+"}+=>+new+{enctype="multipart/form-data"}|code-block|syntax|javascript|1627199|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You should remove the space from the end of enctype attribute: 

<pre><code>new {enctype="multipart/form-data "} =&gt; new {enctype="multipart/form-data"}
</code></pre>

blocks|key|1627239|text|"multipart/form-data“后面的空格才是真正的问题所在...|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1627240|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

An empty space after "multipart/form-data " is the real issue...

blocks|key|1627303|text|你在使用jquery+mobile吗？如果是，则需要将@data_ajax设置为false|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1627304|new+{+enctype+=+"multipart/form-data",+@data_ajax+=+"false"+}|code-block|syntax|javascript|1627305|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

are you using jquery mobile? if yes, you'll need to set @data_ajax to false

<pre><code>new { enctype = "multipart/form-data", @data_ajax = "false" }
</code></pre>

blocks|key|1412678|text|此外，我发现文件上传所在的表单声明必须始终具有|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1412679|new+{enctype="multipart/form-data"}|code-block|syntax|javascript|1412680|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Additionally, I have found that the form declaration in which the file upload lies must always have 

<pre><code>new {enctype="multipart/form-data"}
</code></pre>

blocks|key|1412697|text|使用这个|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1412698|public+ActionResult+Upload(HttpPostedFileBase+excelfile)|code-block|syntax|javascript|1412699|更改HttpPostedFileBase的HttpPostedFile|offset|length|style|CODE|1412700|entityMap^0|0|0|2|I|L|E|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]|$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|N|$]]

use this

<pre><code>public ActionResult Upload(HttpPostedFileBase excelfile)
</code></pre>

change <code>HttpPostedFile</code> for <code>HttpPostedFileBase</code>

blocks|key|1627380|text|以下是上传文件所需的全部内容|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1627381|//in+your+model+
public+partial+class+Profile
{
++++[DisplayName("Image+Upload")]
++++[DataType(DataType.Upload)]+
++++public+HttpPostedFileBase+FileUpload+{+get;+set;+}
}



//+in+your+view
@model+ProjName.Blabla.Profile

@using+(Html.BeginForm("Edit",+"Profile",+FormMethod.Post,+new+{+enctype+=+"multipart/form-data"+}))
{
++++<input+type="file"+name="FileUpload"+id="FileUpload"+value="Choose+File"+class="form-control"+/>

++++<input+type="submit"+value="Save"+class="btn+btn-default"+/>
}|code-block|syntax|javascript|1627382|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Here are all the bits you need to uplaod a file

<pre><code>//in your model 
public partial class Profile
{
 [DisplayName("Image Upload")]
 [DataType(DataType.Upload)] 
 public HttpPostedFileBase FileUpload { get; set; }
}



// in your view
@model ProjName.Blabla.Profile

@using (Html.BeginForm("Edit", "Profile", FormMethod.Post, new { enctype = "multipart/form-data" }))
{
 &lt;input type="file" name="FileUpload" id="FileUpload" value="Choose File" class="form-control" /&gt;

 &lt;input type="submit" value="Save" class="btn btn-default" /&gt;
}
</code></pre>

blocks|key|1627428|text|<form+id="Form1"+method="post"+encType="multipart/form-data"+runat="server">|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1627429|将encType="multipart/form-data"添加到表单中。|unstyled|offset|length|style|CODE|1627430|entityMap^0|0|1|T|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|N|8|@$G|O|H|P|I|J]]|9|@]|A|$]]|$1|K|3|-4|5|F|7|Q|8|@]|9|@]|A|$]]]|L|$]]

<pre><code>&lt;form id="Form1" method="post" encType="multipart/form-data" runat="server"&gt;
</code></pre>

Add <code>encType="multipart/form-data"</code> to your form.

On the View: 

<pre><code>&lt;% =Html.BeginForm("About", "Home", FormMethod.Post, new {enctype="multipart/form-data "})%&gt;
 &lt;input type="file" name="postedFile" /&gt;
 &lt;input type="submit" name="upload" value="Upload" /&gt;
&lt;% Html.EndForm(); %&gt;
</code></pre>

In the Controller, there's something like this:

<pre><code>[AcceptVerbs(HttpVerbs.Post)]
public ActionResult About(HttpPostedFile postedFile)
{
 //but postedFile is null 
 View();
}
</code></pre>

<code>postedFile</code> is null in About(). How do I upload the file?

Uploaded HttpPostedFile is null

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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在视图上：<% =Html.BeginForm("About", "Home", FormMethod.Post, new {enctype="multipart/form-data "})%> <input type="file" name="postedFile" /> <input type="submit"...

问上传的HttpPostedFile为空
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问上传的HttpPostedFile为空EN