Relative Layouts and Density Independent Pixels

Wherever possible you should avoid using hard-coded pixel values. This applies to layouts, Drawables and font sizes.

In particular you should avoid the Absolute Layout class, which depends on the specification of pixel-based coordinates for each child View. Instead, use an alternative Layout manager that describes the child Views relative to each other or the screen edges. For most complex UIs the Relative Layout is likely to be the best solution.

Within your layouts you should also avoid specifying View, Drawable, and font sizes using pixel values. Instead, define the height and width of Views using wrap_content or fill_parent where appropriate, and density-independent pixels (dp) or scale-independent pixels (sp) as required for View and font sizes, respectively.

Density- and scale-independent pixels are means of specifying screen dimensions that will scale to appear the same on hardware using different pixel densities. One density-independent pixel (dp) is equivalent to one pixel on a 160dpi screen. A line specified as 2dp wide will appear as 3 pixels on a display with 240dpi.

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