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Application UI model

Brew MP implements a top visible application UI model, where only one application can draw directly to the display. When an application is successfully started (EVT_APP_START), it becomes top visible or in the foreground. It then receives all keypad and touch and multitouch events and can draw directly to the display.

If another application is started, the system attempts to suspend (EVT_APP_SUSPEND) the previously top-visible application. If the application handles this event, it remains loaded and can still perform all normal tasks. It will not receive keypad, touch, or multitouch events and cannot draw to the display. Applications that do not handle EVT_APP_SUSPEND are unloaded.

Brew MP maintains a list of applications with the top-visible application at the top of the list and the suspended applications in order below. When the top-visible application is closed (EVT_APP_STOP), Brew MP resumes (EVT_APP_RESUME) the next previously suspended application. If that application was unloaded, it is restarted.

Applications can also place themselves in the background. These applications are not in the application history stack, and only come to the foreground if they are started.

A running application can be in one of three states:

  1. Top-visible/foreground: There is only one top-visible application in Brew MP at any given time.
  2. Suspended: There can be multiple. A suspended application can be resumed when the application that caused it to be suspended has terminated.
  3. Background: There can be multiple, and they run in the background.

For more information on suspending and resuming applications, see the Application Management and Technology Guide for Developers, in on the Brew MP website, as well as Event handling function.