我的ASP.NET MVC项目中对foreach循环的Nullreferenceexception [英] Nullreferenceexception on foreach loop in my ASP.NET MVC project

问题描述

 @ model List <   ecommerce.models.products  < span class =code-keyword>>  
 
 <   div     class   = < span class =code-keyword> product-left >  
 @foreach（模型中的var项目）
 { 
 <   div    < span class =code-attribute> class   =  col-md-4 chain-grid >  
 <   a     href   =  @ Url.Action（   详细信息  = ，    uiproductdetail   = ，new {id = item.ProductId}） >  <   img     class   =   img-responsive chain    src   =  @ item.ImageURL    alt   =  @ item.ProductName >  <   / a  >  
 <   span     class   =  star >  <   / span  >  
 <   div     class   =  grid-chain-bottom >  
 <   h6  < span class =code-keyword>>  <   a     href   =  @ Url.Action（    detail   = ，    uiproductdetail   = ，new {id = item.ProductId}） >  @ item.ProductName <   / a  >  <   / h6  >  
 <   div     class   = 星级价格 >  
  <   div     class   =  dolor-grid >  
 <   span    < span class =code-attribute> class   =  actual >  @item.ProductPrice₺<   / span  < span class =code-keyword>>  
 
 <   span     class   =  rating >  
 <   input     type   =  radio    class   =  rating-input    id   =  rating-input-1-5    name   =  rating-input-1 >  
 <  < span class =code-leadattribute> label     for   =  rating-input-1-5    class   =  rating-star1 >  <   / label  >  
 <  输入   类型  =  radio     class   =  rating-input    id   =  rating-input- 1-4   名称  =  rating-input-1 >  
 <   label     for   =  rating-input-1-4    class   =  rating-star1  >  <   / label  >  
 <   input     type   =   radio    class   =  rating-input    id   =  rating-input-1-3    name   =  rating-input-1 >  
 <   label       =  rating-input-1 -3    class   =  rating-star >  <   / label  >  
 <  输入    type   =  radio    class   =  rating-input    id   =  rating-input-1-2    name   =  rating-input-1 >  
 <   label     for   =  rating-input-1-2     class   = < span class =code-keyword> rating-star >  <  < span class =code-leadattribute> / label  >  
 <  输入    type   =  radio < span class =code-attribute>   class   =  rating-input    id   =  rating-input-1-1   名称  =  rating-input-1 >  
 <   label       =  rating-input-1-1    class   =  rating-star >  <   / label  >  
 <   / span  >  
 <   / div  >  
 <   a     class   =  now-get get-cart    href   = ＃ >  ADD TO CART <   / a  >  
 <   div    < span class =code-attribute> class   =  clearfix >  <   / div  >  
 <   / div  >  
 <   / div  >  
 
 <   / div  >  
 
} 
 <   / div  >  

我尝试过：



我工作使用Asp.Net MVC的电子商务项目。

解决方案

这是我们遇到的最常见问题之一，也是我们最不能回答的问题之一，但你最有能力回答自己。



让我解释一下错误的含义：你试图使用变量，属性或方法返回值但它包含null - 这意味着变量中没有类的实例。

它有点像一个口袋：你的衬衫里有一个口袋，用来握笔。如果你进入口袋并发现那里没有笔，你就不能在一张纸上签名 - 如果你尝试的话，你会得到非常有趣的外观！空口袋给你一个空值（这里没有笔！）所以你不能做任何你检索笔通常做的事情。它为什么空？这就是问题 - 可能是你今天早上离开家时忘了拿起你的笔，或者你昨晚把它拿到昨天的衬衫口袋里时可能会把笔留下来。



我们无法分辨，因为我们不在那里，更重要的是，我们甚至看不到你的衬衫，更不用说口袋里的东西了！



回到计算机，你做了同样的事情，不知何故 - 我们看不到你的代码，更不用说运行它了，找不到包含null的东西。

但是你可以 - 而Visual Studio将在这里帮助你。在调试器中运行您的程序，当它失败时，VS将向您显示它发现问题的行。然后，您可以开始查看它的各个部分，以查看哪个值为null，并开始回顾代码以找出原因。因此，在包含错误行的方法的开头放置一个断点，然后从头再次运行程序。这一次，VS会在错误发生前停止，让你通过查看代码来查看你的价值来检查发生了什么。



但我们做不到那 - 我们没有您的代码，如果我们拥有它，我们不知道如何使用它，我们没有您的数据。所以尝试一下 - 看看你能找到多少信息！

你的Model是null。我们无法知道为什么或修复它，您需要查看返回视图的代码以确保传递模型。您还应该学会调试代码，因为这些类型的问题很容易使用调试器来纠正，但我们无法纠正因为我们无法访问您的系统。



掌握Visual Studio 2010中的调试 - 初学者指南 [ ^

@model List<ecommerce.models.products>

<div class="product-left">
    @foreach (var item in Model)
    {
        <div class="col-md-4 chain-grid">
            <a href="@Url.Action(" detail=", " uiproductdetail=", new { id = item.ProductId })"><img class="img-responsive chain" src="@item.ImageURL" alt="@item.ProductName"></a>
            <span class="star"> </span>
            <div class="grid-chain-bottom">
                <h6><a href="@Url.Action(" detail=", " uiproductdetail=", new { id = item.ProductId })">@item.ProductName</a></h6>
                <div class="star-price">
                    <div class="dolor-grid">
                        <span class="actual">@item.ProductPrice₺</span>

                        <span class="rating">
                            <input type="radio" class="rating-input" id="rating-input-1-5" name="rating-input-1">
                            <label for="rating-input-1-5" class="rating-star1"> </label>
                            <input type="radio" class="rating-input" id="rating-input-1-4" name="rating-input-1">
                            <label for="rating-input-1-4" class="rating-star1"> </label>
                            <input type="radio" class="rating-input" id="rating-input-1-3" name="rating-input-1">
                            <label for="rating-input-1-3" class="rating-star"> </label>
                            <input type="radio" class="rating-input" id="rating-input-1-2" name="rating-input-1">
                            <label for="rating-input-1-2" class="rating-star"> </label>
                            <input type="radio" class="rating-input" id="rating-input-1-1" name="rating-input-1">
                            <label for="rating-input-1-1" class="rating-star"> </label>
                        </span>
                    </div>
                    <a class="now-get get-cart" href="#">ADD TO CART</a>
                    <div class="clearfix"> </div>
                </div>
            </div>

        </div>

    }
</div>

What I have tried:

I work on e-commerce project with Asp.Net MVC.

解决方案

This is one of the most common problems we get asked, and it's also the one we are least equipped to answer, but you are most equipped to answer yourself.

Let me just explain what the error means: You have tried to use a variable, property, or a method return value but it contains null - which means that there is no instance of a class in the variable.
It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try! The empty pocket is giving you a null value (no pen here!) so you can't do anything that you would normally do once you retrieved your pen. Why is it empty? That's the question - it may be that you forgot to pick up your pen when you left the house this morning, or possibly you left the pen in the pocket of yesterdays shirt when you took it off last night.

We can't tell, because we weren't there, and even more importantly, we can't even see your shirt, much less what is in the pocket!

Back to computers, and you have done the same thing, somehow - and we can't see your code, much less run it and find out what contains null when it shouldn't.
But you can - and Visual Studio will help you here. Run your program in the debugger and when it fails, VS will show you the line it found the problem on. You can then start looking at the various parts of it to see what value is null and start looking back through your code to find out why. So put a breakpoint at the beginning of the method containing the error line, and run your program from the start again. This time, VS will stop before the error, and let you examine what is going on by stepping through the code looking at your values.

But we can't do that - we don't have your code, we don't know how to use it if we did have it, we don't have your data. So try it - and see how much information you can find out!

Your Model is null. There is no way of us to know why that is or to fix it, you'll need to look at the code that returns the view to ensure a model is passed. You should also learn to debug your code as these types of problems are simple for you to rectify using the debugger, but impossible for us to rectify as we can't access your system.

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]

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