Actions in modern GUI applications, it happens quite regularly that a user action (like “save file”) can be invoked by several means: by choosing a menu item, clicking a toolbutton or pressing a hotkey. To avoid multiple implementations, all necessary items like menu text, keyboard shortcut, icon, etc., are collected in one so-called action. Instead of implementing a toolbutton or a menu entry, one simply adds the action to the relevant menu or toolbar, and it will appear as a menu entry or toolbutton, depending on the context.
Signals and Slots to allow for component programming, Qt uses (and invented) the following concept. Whenever an object changes status it issues a signal (for example, a button sends a clicked() signal when it changes status from idle to “received a mouse click”). Other objects can connect specially marked functions, or so-called slots, to signals in which they are interested; such a clicked() signal issued by the toolbutton used to open a file would be connected to a fileOpen() slot. As signals and slots are not standard C++ features, the meta object compiler, moc, is required as a preprocessor that converts the specific notation to C++. This is why Makefiles, even for simple Qt programs, become quite complex.
Statustip help text that appears in the statusbar when the user hesitates with the mouse over a widget item like a toolbutton or a menu item.
Toolbutton a button in a toolbar, often marked with an icon, that lets the user issue a command like “save file”.
Tooltip balloon help—a note, commonly on a yellow background that is issued when the user hesitates with the mouse over a widget item like a toolbutton or a menu item.
