I'm using a foreach loop to populate each row in a DataGridView with a string. I need to search the DataGridView to make sure that I don't add a string that is already there. What is the best way to do this?

Here is my code so far:

foreach (String file in openFileDialog.FileNames)
    {                                    
        // todo: make sure file string does not already exist in DataGridView
        dataGridView1.Rows.Add();
        dataGridView1.Rows[i].Cells[1].Value = file;
        i++;
    }