WPF textbox清空

选中checkbox1后，textbox1内容清空且变为只读状态

<CheckBox x:Name="cb" Width="20" Height="20" Checked="cb_Checked"/>
        <TextBox x:Name="test" Width="100" Height="20" />


private void cb_Checked(object sender, RoutedEventArgs e)
        {
            if (((CheckBox)sender).IsChecked.Value)
            {
                this.test.Text = "";
                this.test.Focus();
            }
        }