Question

How do I restrict file types with the HTML input file type?

I have this

<input type="file" id="fileUpload" name="fileUpload" size="23" accept="Calendar/ics"/>

I am trying to restrict the type to only the iCalendar format type.

I also want to check it on the server side. How do I do this in ASP.NET MVC?

Answer 1

Unfortunately, you can’t restrict the file extension like you can in a standard file browser dialog. You can, however, check the extension once the user selects a file.

You can add this event handler.

filebox.Attributes.Add("onchange", "fileSelectedChanged(this);");

and this JavaScript function

function fileSelectedChanged(obj) {
    var filePath = obj.value;

    var ext = filePath.substring(filePath.lastIndexOf('.') + 1).toLowerCase();
    if(ext != 'csv') {
        alert('Only files with the file extension CSV are allowed');
    } else {
        document.getElementById('form1').submit();
    }
}

You should also check it on the server, using:

filebox.PostedFile.FileName

and:

filebox.PostedFile.ContentType