Activity Objects and Navigating the User Interface Hierarchy

Most mobile handset user interfaces consist of a linked web, or hierarchy, of "screens"—user interface views that occupy the whole screen, except for areas where titles and indicator icons are displayed and where soft-key labels (if any) are displayed. Usually, these hierarchies are implemented by a single program that manages a "stack" of screens backward from the current screen (and sometimes forward, as well, as in an iPod-like UI). Intent and Activity objects work together, using inter-process communication, to link different parts of different applications' user interfaces into a coherent user experience with navigation that is unified and seamless when moving between applications. In this section we'll show how UI navigation and inter-process communication go hand-in-hand.

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