Implementing the functions for the actions

In the previous section, we added several actions to the menu and toolbar. However, if we click on these actions, nothing happens. That's because we have not written any handler for them yet. Qt uses a signal and slot connection mechanism to establish the relationship between events and their handlers. When users perform an operation on a widget, a signal of that widget will be emitted. Then, Qt will ascertain whether there is any slot connected with that signal. The slot will be called if it is found. In this section, we will create slots for the actions we have created in the preceding sections and make connections between the signals of the actions to these slots respectively. Also, we will set up some hotkeys for frequently used actions.