如何在ASP.NET MVC5中上传多个文件 [英] How to upload multiple files in ASP.NET MVC5

问题描述

尝试使用asp.net mvc5中的ajax.beginform上传文件时出现此错误对象引用未设置为对象的实例



这是我的观点

Hi, been getting this error when trying to upload files using ajax.beginform in asp.net mvc5 "Object reference not set to an instance of an object"

here's my view

@using (Ajax.BeginForm("submitSchlAd1", "Ministry", new AjaxOptions { HttpMethod = "POST", UpdateTargetId = "error" }, new { @id = "schlregdiv", @class = "form-horizontal" }))
            {
                <label for="inputfile" class="col-sm-4 control-label">Admin's Passport</label>
                <input name="ad1file" type="file" onchange="imgdisp(this)" required>
                
                <label for="inputfile" class="col-sm-4 control-label">NOK Passport</label>
                <input name="ad1file" type="file" onchange="imgdispnok(this)" required>

                <button type="submit" class="btn btn-default">Submit</button>
            }

我的尝试：



这里是我的控制器功能

What I have tried:

and here's my controller function

[HttpPost]
        public ActionResult submitSchlAd1(IEnumerable<HttpPostedFileBase> ad1file)
        {
            FormData fd = new FormData();
            
            try
            {
                    foreach (var file in ad1file)
                    {
                        if (file.ContentLength > 0)
                        {
                            string filename = Path.GetFileName(file.FileName);
                            var path = Path.Combine(Server.MapPath("~/Content/UploadImg"), filename);
                            file.SaveAs(path);
                        
                            fd.ad1pass = System.IO.File.ReadAllBytes(path);
                        }
                    }
                    return View("Court");                
            }
            catch (Exception ex)
            {
                return View("Home");
            }
        }

i不知道我做错了什么，请指出我。



感谢您的一切帮助

i don't know what i'm doing wrong, please point out to me.

Thanks for every assistance

推荐答案

您没有显示带有对象参考消息的异常没有设置为对象的实例被抛出。



不用担心。这是检测和修复的最简单的案例之一。它只是意味着某些引用类型的某个成员/变量通过使用及其实例（非静态）成员进行解引用，这需要此成员/变量为非null，但实际上它似乎为null。只需在调试器下执行它，它将停止抛出异常的执行。在该行上设置一个断点，重新启动应用程序并再次到达这一点。评估下一行中涉及的所有引用，并查看哪一个为null，而不需要为null。解决这个问题之后，修复代码：要么确保将成员/变量正确初始化为非空引用，要么将其检查为null，如果为null，则执行其他操作。



另请参阅：想要在按钮点击时显示下一条记录。但是如果下一个记录功能的条件对象引用未设置为对象的实例则会出错。



有时候，你不能这样做在调试器下，由一个或另一个原因。一个非常讨厌的情况是，只有在调试信息不​​可用时构建软件时才会出现问题。在这种情况下，你必须使用更难的方式。首先，你需要确保你永远不会通过静默处理异常来阻止异常的传播（这是开发人员对自己的犯罪，但很常见）。您需要在每个线程的最顶层堆栈帧上捕获绝对所有异常。如果处理类型 System.Exception 的异常，则可以执行此操作。在处理程序中，您需要记录所有异常信息，尤其是 System.Exception.StackTrace ：

http://msdn.microsoft.com/en-us/library/system.exception.aspx ，

http://msdn.microsoft.com/en-us/library/ system.exception.stacktrace.aspx 。



堆栈跟踪只是一个字符串，显示从throw语句到处理程序的异常传播的完整路径。通过阅读，您总能找到目的。对于日志记录，使用类 System.Diagnostics.EventLog ：

http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx 。



祝你好运，

-SA

You did not show where the exception with the message "Object reference not set to an instance of an object" is thrown.

Not to worry. This is one of the very easiest cases to detect and fix. It simply means that some member/variable of some reference type is dereferences by using and of its instance (non-static) members, which requires this member/variable to be non-null, but in fact it appears to be null. Simply execute it under debugger, it will stop the execution where the exception is thrown. Put a break point on that line, restart the application and come to this point again. Evaluate all references involved in next line and see which one is null while it needs to be not null. After you figure this out, fix the code: either make sure the member/variable is properly initialized to a non-null reference, or check it for null and, in case of null, do something else.

Please see also: want to display next record on button click. but got an error in if condition of next record function "object reference not set to an instance of an object".

Sometimes, you cannot do it under debugger, by one or another reason. One really nasty case is when the problem is only manifested if software is built when debug information is not available. In this case, you have to use the harder way. First, you need to make sure that you never block propagation of exceptions by handling them silently (this is a crime of developers against themselves, yet very usual). The you need to catch absolutely all exceptions on the very top stack frame of each thread. You can do it if you handle the exceptions of the type System.Exception. In the handler, you need to log all the exception information, especially the System.Exception.StackTrace:
http://msdn.microsoft.com/en-us/library/system.exception.aspx,
http://msdn.microsoft.com/en-us/library/system.exception.stacktrace.aspx.

The stack trace is just a string showing the full path of exception propagation from the throw statement to the handler. By reading it, you can always find ends. For logging, it's the best (in most cases) to use the class System.Diagnostics.EventLog:
http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx.

Good luck,

—SA

你得到了错误，因为 ad1file 对象是 null 。

为了从<获取文件code>表单，您必须添加 enctype =multipart / form-data [ ^ ]属性

You are getting the error because ad1file object is null.
In order get the files from the Form, you will have to add enctype="multipart/form-data[^] attribute

@using (Ajax.BeginForm("submitSchlAd1", "Home", new AjaxOptions { HttpMethod = "POST", UpdateTargetId = "error" }, new { @enctype = "multipart/form-data" , @id = "schlregdiv", @class = "form-horizontal" }))
   {

你无法通过ajax上传文件，javascript无法访问文件系统以序列化数据。 Google如何使用MVC和jQuery上传文件，因为如果客户端有html5，这是可能的，如果他们没有html5，你需要使用专为旧版浏览器的ajax上传而设计的插件。



如果只是多件事不起作用，请尝试给不同的输入不同的名称，或称之为ad1File [0]和ad1File [1]

You can't upload files via ajax that way, javascript doesn't have access to the file system in order to serialise the data. Google how to upload files using MVC and jQuery, as this is possible if the client has html5, if they don't have html5 you'll need to use a plug-in designed for ajax uploads for older browsers.

If it's just the multiple thing not working, try giving the different inputs different names, or call them "ad1File[0]" and "ad1File[1]"

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