Provides features for managing event taps—filters for observing and altering the stream of low-level user input events in macOS.
Event taps make it possible to monitor and filter input events from several points within the system, prior to their delivery to a foreground application. Event taps complement and extend the capabilities of the Carbon event monitor mechanism, which allows an application to observe input events delivered to other processes (see the function GetEventMonitorTarget()).
Event taps are designed to serve as a Section 508 enabling technology. For example, consider a software system to assist a person with language impairments, designed to perform keyboard filtering with spoken review. Such a system could use an event tap to monitor all keystrokes, perform dictionary checks and matches, and recite the assembled word back to the user on detection of a word break in the input stream. If acceptable to the user, as indicated by an additional input keystroke or other gesture, the events would be posted into the system for delivery to the foreground application.
Introduced in OS X version 10.4, event taps provide functionality similar to the Win32 functions
SetWinEventHook when used to establish an out-of-context event hook, and
SendInput. Quartz Event Services also includes an older set of event-related functions declared in the file
CGRemoteOperation.h. These functions are still supported, but they are not recommended for new development.