Windows.Forms’ DialogResult does not have OK as a member

I found this code to show up a “file browse” dialog from C#:

OpenFileDialog ofd = new OpenFileDialog();
DialogResult b = ofd.ShowDialog();
if (b == DialogResult.OK)
{
  CopySourceFiles.Text = ofd.FileName;
}

The problem was that it was giving an error saying that DialogResult did not have a member named OK. So I had to fully qualify DialogResult as the following snippet shows:

OpenFileDialog ofd = new OpenFileDialog();
System.Windows.Forms.DialogResult b = ofd.ShowDialog();
if (b == System.Windows.Forms.DialogResult.OK)
{
  CopySourceFiles.Text = ofd.FileName;
}