虽然上传文件objet引用未设置实例错误 [英] While uploading file objet reference is not set instance error

问题描述

我正在使用文件上传控件上传文件，我有一个按钮可以将其上传到服务器上但是它在代码的第一行出错了

I am uploading File using file Upload control and I have one button to upload it on server but but it gives error at first line in code as

Object reference not set to an instance of an object

我有文件上传控制为

I have File upload control as

<asp:FileUpload ID="fileuploadDoc" class="form-control" runat="server" />

还有服务器端验证为

also Have server side Validation as

<asp:RequiredFieldValidator ID="RequiredFieldVal" ControlToValidate="fileuploadDoc" runat="server" ErrorMessage="Choose File" ValidationGroup="valProPic" Display="Dynamic" Font-Size="Smaller" ForeColor="#CC0000"></asp:RequiredFieldValidator>
                                <asp:RegularExpressionValidator ID="RegularExpressionValidator6" ControlToValidate="fileuploadDoc" ErrorMessage="Only .png & .jpg images are alloweded" ValidationExpression="([a-zA-Z0-9\s_\\.\-:])+(.png|.jpg)$" runat="server" ValidationGroup="valProPic" Display="Dynamic" Font-Size="Smaller" ForeColor="#CC0000" />

和按钮

and button as

<asp:LinkButton runat="server" ID="btnaddfileuplod" ValidationGroup="valProPic" CssClass="btn btn-primary" OnClick="btnaddfileuplod_Click">Upload</asp:LinkButton>
                               <asp:LinkButton runat="server" ID="btnDeleteProPic" CausesValidation="false" CssClass="btn btn-default" OnClick="btnDeleteProPic_Click">Delete</asp:LinkButton>

我的尝试：



Uplaod按钮为

What I have tried:

Uplaod Button as

<asp:LinkButton runat="server" ID="btnaddfileuplod" ValidationGroup="valProPic" CssClass="btn btn-primary" OnClick="btnaddfileuplod_Click">Upload</asp:LinkButton>

点击Handlar as

On click Handlar as

protected void btnaddfileuplod_Click(object sender, EventArgs e)
    {
        int size1 = fileuploadDoc.PostedFile.ContentLength;
        bool flag = false;
        if (size1 > 0)
        {
            try
            {
                string imgPath = "";
                string filename = Path.GetFileName(fileuploadDoc.PostedFile.FileName);
                string extension = System.IO.Path.GetExtension(fileuploadDoc.FileName);
                imgPath = "img/" + Common.Get_SystemDate_IndianFormate().ToString("ddMMyyhhmmss") + extension;

                fileuploadDoc.SaveAs(Server.MapPath(imgPath));

                flag = true;
                lblUploadedProPicPath.Text = imgPath;
                imgProfile.ImageUrl = imgPath;
            }
            catch (Exception ex) { flag = false; }
        }
        if (!flag)
        {
            AlertMesg(false, "File uploading fail. Please try again...!");
        }
    }

另一页我有相同的按钮和相同代码它工作正常

但是这里它首先给出异常行

for another page I have Same Button and same code It Working Fine there
but here it is giving exception at first Line

推荐答案

runat =serverValidationGroup =valProPic Display =DynamicFont-Size =SmallerForeColor =＃CC0000/>

" runat="server" ValidationGroup="valProPic" Display="Dynamic" Font-Size="Smaller" ForeColor="#CC0000" />

和按钮

and button as

<asp:LinkButton runat="server" ID="btnaddfileuplod" ValidationGroup="valProPic" CssClass="btn btn-primary" OnClick="btnaddfileuplod_Click">Upload</asp:LinkButton>
                               <asp:LinkButton runat="server" ID="btnDeleteProPic" CausesValidation="false" CssClass="btn btn-default" OnClick="btnDeleteProPic_Click">Delete</asp:LinkButton>

我尝试过：



Uplaod按钮为

What I have tried:

Uplaod Button as

<asp:LinkButton runat="server" ID="btnaddfileuplod" ValidationGroup="valProPic" CssClass="btn btn-primary" OnClick="btnaddfileuplod_Click">Upload</asp:LinkButton>

单击Handlar作为

On click Handlar as

protected void btnaddfileuplod_Click(object sender, EventArgs e)
    {
        int size1 = fileuploadDoc.PostedFile.ContentLength;
        bool flag = false;
        if (size1 > 0)
        {
            try
            {
                string imgPath = "";
                string filename = Path.GetFileName(fileuploadDoc.PostedFile.FileName);
                string extension = System.IO.Path.GetExtension(fileuploadDoc.FileName);
                imgPath = "img/" + Common.Get_SystemDate_IndianFormate().ToString("ddMMyyhhmmss") + extension;

                fileuploadDoc.SaveAs(Server.MapPath(imgPath));

                flag = true;
                lblUploadedProPicPath.Text = imgPath;
                imgProfile.ImageUrl = imgPath;
            }
            catch (Exception ex) { flag = false; }
        }
        if (!flag)
        {
            AlertMesg(false, "File uploading fail. Please try again...!");
        }
    }

另一页我有相同的按钮和相同代码它在那里运行良好

但这里它在第一行提供异常

for another page I have Same Button and same code It Working Fine there
but here it is giving exception at first Line

这是我们被问到的最常见的问题之一，它也是一个我们最没有能力回答，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，你呢用来握笔。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！

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!

就像'Griff说的那样，在按钮点击处理程序的第一行代码上设置一个断点。开始查看变量和对象的内容，很容易找到哪个部分为空。



你不能使用没有对象的方法或属性不存在，或者是空的。你的代码假设一切都按你期望的方式工作。情况并非如此。现在由您来使用调试器来了解您的代码是如何工作的。

Like 'Griff said, set a breakpoint on the first line of code in your button click handler. Start looking at the contents of variables and objects and it'll be very easy to find which piece is null.

You cannot use methods or properties of an object that doesn't exist, or is null. You're code is assuming everything is working the way YOU expect. That isn't the case. Now it's up to YOU to use the debugger to understand how your code is really working.

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