For the fileupload Server Control example, Asp.net cannot find the control for uploading files,

<Input id = "upfile4" type = file runat = "server">
It is automatically generated. I can use request. Form [upfile4] to access the value, but I cannot find the control using request. files. I can see that the value of request. Files. Count is 0.
Upfile4 is automatically generated.
Request. form can be found, but request. Files cannot be found. What is that?
On another page, the access is successful, CodeIs the same,
I add a fixed <input id = "upfil" type = file runat = "server">, request. files. if the value of count is still 0, I suspect there is a problem with my settings. It is not a problem with the code. I found the form attribute and finally found it.