combobox中动态加入几个checkbox，实现下拉框多选

combobox中动态加入几个checkbox，实现下拉框多选，将一个checkbox选中时其内容就会在combobox中显示出来，将另一个checkbox选中时其内容会跟在第一个checkbox的内容后面一起在combobox中显示出来。

前台代码：

　　　  <ComboBox Height="23" Name="cmbText" Width="120" IsReadOnly="False"  >
                <CheckBox Name="chk1" Content="aaaa" Checked="chk1_Checked"/>
                <CheckBox Name="chk2" Content="bbbb"  Checked="chk1_Checked"/>
                <CheckBox Name="chk3" Content="cccc"  Checked="chk1_Checked"/>
                <CheckBox Name="chk4" Content="dddd"  Checked="chk1_Checked"/>
            </ComboBox>

后台代码：

 　　StringBuilder sb = new StringBuilder();

        //选中的值就添加到下拉框的选择状态。
        private void chk1_Checked(object sender, RoutedEventArgs e)
        {
            CheckBox chk = (CheckBox)sender;

            sb.Append(chk.Content.ToString());

            cmbText.Text = string.Empty;
            cmbText.Items.Insert(cmbText.Items.Count, new ComboBoxItem() { Content = sb.ToString() });
            cmbText.Text = sb.ToString();
            foreach (var item in cmbText.Items)
            {
                if (item is CheckBox)
                {
                    CheckBox chks = item as CheckBox;
                    chks.Visibility = Visibility.Visible;
                }
                else
                {
                    ComboBoxItem c = item as ComboBoxItem;
                    c.Visibility = Visibility.Hidden;
                }
            }
        }

有一些细节需要优化。