Now that you have written some Android code you
View, and the layout and widget subclasses of
View are among the most important classes
in Android. Typically, an Android user interface is built from widget views
organized in layouts: a
ListView in a
LinearLayout, for instance. A single
hierarchy of view objects gets loaded from a resource (or created by code)
Activity is started. It is
initialized and displayed on the device screen.
For small screens, this is fine: users move from
screen to screen to access different parts of a program’s UI, and the
Activity class (Android’s concept of a
task) supports a back stack that enables quick and intuitive traversal
through the strictly tree-structured interface. This changes completely,
however, when the UI is spread over the surface of a larger tablet screen.
Some parts of the screen remain constant over longer durations than others.
Some parts of the screen determine the contents of other parts. A card-stack
metaphor just doesn’t cut it.
It is entirely possible to implement UIs in which
some parts of the screen change in response to activities in another part,
simply by showing and hiding views. Android’s developers decided, however,
that they needed more than just convention to encourage great large-screen
UIs with a consistent feel and behavior. To facilitate this new kind of
interaction, they introduced a new feature based on the
Fragment class, as part of the ...