How to correctly use the ASP.NET FileUpload control

My solution in code behind was:

System.Web.UI.WebControls.FileUpload fileUpload;

I don't know why, but when you are using FileUpload without System.Web.UI.WebControls it is referencing to YourProject.FileUpload not System.Web.UI.WebControls.FileUpload.

Adding a FileUpload control from the code behind should work just fine, where the HasFile property should be available (for instance in your Click event).

If the properties don't appear to be available (either as a compiler error or via intellisense), you probably are referencing a different variable than you think you are.

Instead of instantiating the FileUpload in your code behind file, just declare it in your markup file (.aspx file):

<asp:FileUpload ID="fileUpload" runat="server" />

Then you will be able to access all of the properties of the control, such as HasFile.

ASP.NET controls should rather be placed in aspx markup file. That is the preferred way of working with them. So add FileUpload control to your page. Make sure it has all required attributes including ID and runat:

<asp:FileUpload ID="FileUpload1" runat="server" />

Instance of FileUpload1 will be automatically created in auto-generated/updated *.designer.cs file which is a partial class for your page. You usually do not have to care about what's in it, just assume that any control on an aspx page is automatically instantiated.

Add a button that will do the post back:

<asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />

Then go to your *.aspx.cs file where you have your code and add button click handler. In C# it looks like this:

protected void Button1_Click(object sender, EventArgs e)
{
  if (this.FileUpload1.HasFile)
  {
    this.FileUpload1.SaveAs("c:\\" + this.FileUpload1.FileName);
  }
}

And that's it. All should work as expected.