用 DBGrid 的 OnColExit,某单元格失去焦点时。从下面的说明看，行的变化也会触发
如果行变化不触的话，可以用 相应 Table 中的事件。
Occurs just before a cell in the grid loses input focus.
property OnColExit: TNotifyEvent;
Description
Write an OnColExit event handler to take specific action when a cell is about to lose focus. For example, use OnColExit to post edits to the underlying dataset when the user leaves a cell, rather than waiting for the user to leave the record.
A cell loses focus when
?The user navigates out of the cell using the keyboard. For example, when the user presses the Tab key or the Home key.
?The user clicks the mouse button down in another cell.
?The SelectedField or SelectedIndex property is set.
When the selected cell in the data-aware grid changes, first the OnColExit event occurs. Then the values of SelectedField and SelectedIndex are updated. Finally the OnColEnter event occurs. Thus, in an OnColExit event handler, the SelectedField or SelectedIndex property can be used to determine which column is about to lose focus.
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