文档中是这样描述的:
void QAction::trigger () [slot]
This is a convenience slot that calls activate(Trigger).
void QAction::triggered ( bool checked = false ) [signal]
This signal is emitted when an action is activated by the user; for example, when the user clicks a menu option, toolbar button, or presses an action's shortcut key combination, or when trigger() was called. Notably, it is not emitted when setChecked() or toggle() is called.
If the action is checkable, checked is true if the action is checked, or false if the action is unchecked.