In an event driven system I/O is user driven, unlike a tty interface where I/O is permitted only at times chosen by the program. These events may require considerable redrawing of the screen. This is the role of the window manager. A window manager is most conveniently implemented as a class library.
There is a hierarchical arrangement of widgets (windows, buttons, sliders etc.) that receive messages. This hierarchy is well exemplified in the Tk system where the syntax of the interface construction carries the hierarchy within it. Thus a widget within a window that receives a message passes the message on to the window to which it belongs. Although if it knows of another window it can pass the message there instead.
Event dispatching can be handled in one of three ways.
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Last Changed: 8 May 1995