WPF DataGrid DataGridComboBoxColumn取值问题

[XiaoZuo123456789]

后台：窗口打开事件
DataGridComboBoxColumn cm = new DataGridComboBoxColumn();
cm.Header = "code";
cm.SelectedValueBinding = new Binding("code");
cm.DisplayMemberPath = "name";
cm.SelectedValuePath = "code";

this.data.Columns.Add(cm);

DataGridComboBoxColumn dd = data.Columns[0] as DataGridComboBoxColumn;
DataTable dt = new DataTable();
dt.Columns.Add("code");
dt.Columns.Add("name");
dt.Rows.Add("1", "a");
dt.Rows.Add("2", "b");
dt.Rows.Add("3", "c");
dt.Rows.Add("4", "d");
dd.ItemsSource = dt.DefaultView;


DataTable dte = new DataTable();

dte.Columns.Add("code1");
dte.Columns.Add("tex");
dte.Rows.Add("1","a");
dte.Rows.Add("2", "b");
dte.Rows.Add("3", "c");
dte.Rows.Add("4", "d");
data.ItemsSource = dte.DefaultView;
前台：
<DataGrid Name="data" Margin="172,10,102,125"/>
<TextBox Name="txt1" Width=" 120" Height=" 24" Margin="10,156,629,195"/>
<Button Content="Button" HorizontalAlignment="Left" Margin="10,108,0,0" VerticalAlignment="Top" Width="75" Click="Button_Click_2"/>


我想单击按钮获取到下拉框选择的值
还有就是 能够添加指定列 或者最后一列嘛

[XiaoZuo123456789]

求大神解答

[XiaoZuo123456789]

分不够 我可以加的

[XiaoZuo123456789]

都没人嘛