I've received a couple of requests lately about how to implement drag-and-drop multiple file uploads in Internet Explorer from within managed code. Fortunately for me, someone else has already taken the liberty of writing an article on the subject at large: Host Secure, Lightweight Client-Side Controls in Microsoft Internet Explorer. Just a couple of tweaks and it'll be accepting files via drag and drop too.

In MultiUploadCtrl.cs, we need to enable drag and drop processing in the user control. Setting AllowDrop=True handles that in one swoop, now all that's left is the plumbing to handle the dropped files. For the events, DragEnter and DragDrop, the following should work well:

private void MultiUploadCtrl_DragEnter(object sender, System.Windows.Forms.DragEventArgs e)
{
  if (e.Data.GetDataPresent("FileDrop"))
    e.Effect = DragDropEffects.Copy;
  else
    e.Effect = DragDropEffects.None;
}

private void MultiUploadCtrl_DragDrop(object sender, System.Windows.Forms.DragEventArgs e)
{
  new FileIOPermission(PermissionState.Unrestricted).Assert();
  foreach (string fileListItem in (e.Data.GetData("FileDrop") as string[]))
  {
    if (!fileTable.Contains(fileListItem))
    {
      AddFile(fileListItem);
    }
  }
  CodeAccessPermission.RevertAssert();
  UpdateFileSizeDescription();
}