datagridview绑定后添加行

DataTable dt =new DataTable();

private void Form1_Load(object sender, EventArgs e)
{
dt.Columns.Add("ColumnName");
dt.Rows.Add("值one");
dt.Rows.Add("值two");
dataGridView1.DataSource = dt;
}

private void button1_Click(object sender, EventArgs e)
{
dt = (DataTable)this.dataGridView1.DataSource;
DataRow row = dt.NewRow();
int rowscount = dt.Rows.Count;
dt.Rows.InsertAt(row, rowscount);
dt.Rows[dataGridView1.Rows.Count - 2][0] = "2";//默认值

//dataGridView1.Rows.Add();
}