Legacy Document

Inside Macintosh: Macintosh Toolbox Essentials /

Chapter 1 - Introduction to the Macintosh Toolbox / Overview of the Macintosh Toolbox

Events

At the core of every Macintosh application is the application's event loop. The event loop is that piece of code in an application that processes and responds to user actions and other events. You can use the Event Manager to retrieve information about these actions. For example, you can get information that tells your application whether the user pressed a key or the mouse button, whether one of your application's windows needs updating as a result of the user moving windows, or whether some other hardware or software action requires a response from your application.

You should structure your application so that it can respond to events and so that the user is able to perform tasks in any order. For example, a user should be able to type text in a window, select a graphic and copy it, open a new document, paste in the graphic, open another document, and then go back to the first window to select text and change its typeface, size, or style.

Your application should respond to events in a way that lets the user switch between your application and others whenever the user chooses to do so (for example, by clicking in a window belonging to another application). Your application should also yield time to other applications when it isn't busy. System software provides a cooperative multitasking environment that allows users to switch between many open applications and that allows applications to receive available processing time when other applications aren't using the processor. System software coordinates the scheduling of processing time between your application and other applications.

You can also let your application communicate with other applications in order to request services or information from another application or to provide services to other applications. You can use the Event Manager or Apple Event Manager to do this.

The chapter "Event Manager" in this book describes how to structure your event loop and event-handling code to receive notification of user actions and changes in the processing status of your application, how to communicate with other applications, and how to respond to these events.