Efficient Event Registration: Motivation

Suppose we have a GUI that allows us to Cut and Paste

The “Cut” action can be performed by (1) a menu item and (2) a button.

Of course, we can only

cut when we’ve highlighted

an object or area of text,

so sometimes our

cut option is enabled,

sometimes it’s disabled

Enabled

Disabled

. . . We have to keep the

button and menu in sync.

If more objects are added that perform “Cut” operations, we have to rewrite the program