列表头全选和取消全选

• 有详细说明和Demo;
  参考：
  Toggling the States of all CheckBoxes Inside a DataGridView Column
  

More than a year and a half ago, I wrote an article, Selecting/ Deselecting all the CheckBoxes Inside a GridView for Web Forms. Last month, I got a chance to implement the same functionality for the DataGridView control for Windows Forms. Initially, I thought it would be as easy as in the case of the GridView for Web Forms, but it wasn't. It is a bit tricky in the case of the DataGridView control for Windows Forms. E.g., adding a header CheckBox in a column of the DataGridView control is not a straightforward job. So after doing a lot of research work and spending a lot of time on studying the functionality of the control, I have finally arrived at the following solution. All modifications and clarifications are most welcome!