问题
I am trying to implement a CheckBox ComboBox. I followed this link as a reference
http://www.codeproject.com/Articles/31105/A-ComboBox-with-a-CheckedListBox-as-a-Dropdown?msg=4152597#xx4152597xx
But there are some problems with this example.
1) After the drop-down list is shown, the very first mouse single-click to change the selected item's check-status always fails to do so, but succeeding single-clicks are fine. It seems the very first single-click is swallowed. I did some trace works but failed to find an answer.
2) The form loses focus when the list opens.
来源：https://stackoverflow.com/questions/9214564/combobox-with-checkboxes-in-winforms