当尝试通过c＃从html访问上传文件时，如何修复visual studio中的Null Reference错误？

Question

我一直在建立一个网站，并尝试在我的注册页面添加一个字段，用户可以上传自己的个人资料照片。我打算将给定的照片保存到项目中的文件夹中，但无法弄清楚为什么我会继续获得NullReferenceException。

protected void Page_Load(object sender, EventArgs e)
{
    string gender, Fname, Lname, username, pass, Sorientation, country;
    if (Request.Form["sub"] != null)
    {
        HttpPostedFile profile;
        profile = Request.Files["profile-image"];
        string FileName = System.IO.Path.GetFileName(profile.FileName);
        profile.SaveAs(Server.MapPath(System.IO.Path.Combine("D:/.... /Profiles/", FileName)));    `
    }
    //..
}

const realFileBtn = document.getElementById("profile-image");
const customBtn = document.getElementById("custom-button");
const customTxt = document.getElementById("custom-text");

customBtn.addEventListener("click", function () {
    realFileBtn.click();
});

realFileBtn.addEventListener("change", function () {
    if (realFileBtn.value) {
        customTxt.innerHTML = realFileBtn.value.match(
            /[\/\\]([\w\d\s\.\-\(\)]+)$/
        )[1];
    } else {
        customTxt.innerHTML = "No image was chosen. Profile will be set as default!";
    }
});

<input type="file" id="profile-image" name="profile-image" hidden="hidden" accept=".gif,.jpg,.jpeg,.png,.BMP"  />
<button type="button" id="custom-button" style=" padding: 4px;
  color: transparentize( rgba(255,255,255,1),0.8 );
  background-color: rgb(255, 96, 207);
  border-radius: 10px;
  cursor: pointer;">Upload custom image </button>
<br />
<span id="custom-text">No image was chosen. Profile will be set as default!</span>

Answer 1

我猜您的表单翻译如下：

确保你有enctype作为multipart/form-data

<form action="enter path" method="post" enctype="multipart/form-data">
    <input  type="file" id="profile-image" name="profile-image" hidden="hidden" accept=".gif,.jpg,.jpeg,.png,.BMP" />
    <button type="submit" >Submit</button>
</form>

进行空检查以避免NullReferenceException

if (Request.Files.Count > 0)
{
    HttpPostedFileBase profile;
    profile = Request.Files[0]; 

    if (profile != null && profile.ContentLength > 0)
    {
        var fileName = Path.GetFileName(profile.FileName);
        profile.SaveAs(Server.MapPath(Path.Combine("D:/.... /Profiles/", fileName)));
    }
}

Answer 2

您需要使用asp:FileUpload控件而不是<input type="file" />才能根据请求获取发布的文件。

<asp:FileUpload id="ProfileImage" runat="server" id="profile-image" name="profile-image" hidden="hidden" accept=".gif,.jpg,.jpeg,.png,.BMP" /> 

然后您可以通过ProfileImage控件访问上传的文件

protected void Page_Load(object sender, EventArgs e)
{
    //..
    //check if user sent a file
    if (ProfileImage.HasFile)
    {
        HttpPostedFile profile = ProfileImage.PostedFile;
        string FileName = System.IO.Path.GetFileName(profile.FileName);
        profile.SaveAs(Server.MapPath(System.IO.Path.Combine("D:/.... /Profiles/", FileName)));
    }
    //..
}