Most programming models support event-driven programming only through in-
version of control. Instead of calling blocking operations (e.g. for obtaining user
input), a program merely registers its interest to be resumed on certain events
(e.g. an event signaling a pressed button, or changed contents of a text field).
In the process, event handlers are installed in the execution environment which
are called when certain events occur. The program never calls these event han-
dlers itself. Instead, the execution environment dispatches events to the installed
handlers. Thus, control over the execution of program logic is "inverted".

[b]Virtually all approaches based on inversion of control suffer from the following
two problems[/b]: First, the interactive logic of a program is fragmented across
multiple event handlers (or classes, as in the state design pattern [13]). Second,
control flow among handlers is expressed implicitly through manipulation of
shared state [10].