Книга: Beginning Android

Galleries, Give or Take the Art

Galleries, Give or Take the Art

The Gallery widget is not one ordinarily found in GUI toolkits. It is, in effect, a horizontally-laid-out listbox. One choice follows the next across the horizontal plane, with the currently-selected item highlighted. On an Android device, one rotates through the options through the left and right D-pad buttons.

Compared to the ListView, the Gallery takes up less screen space while still showing multiple choices at one time (assuming they are short enough). Compared to the Spinner, the Gallery always shows more than one choice at a time.

The quintessential example use for the Gallery is image preview — given a collection of photos or icons, the Gallery lets people preview the pictures in the process of choosing one.

Code-wise, the Gallery works much like a Spinner or GridView. In your XML layout, you have a few properties at your disposal:

• android:spacing controls the number of pixels between entries in the list.

• android:spinnerSelector controls what is used to indicate a selection — this can either be a reference to a Drawable (see the resources chapter) or an RGB value in #AARRGGBB or similar notation.

• android:drawSelectorOnTop indicates if the selection bar (or Drawable) should be drawn before (false) or after (true) drawing the selected child — if you choose true, be sure that your selector has sufficient transparency to show the child through the selector, otherwise users will not be able to read the selection.

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