Devices and Displays

Android powers millions of phones, tablets, and other devices in a wide variety of screen sizes and form factors. By taking advantage of Android's flexible layout system, you can create apps that gracefully scale from large tablets to smaller phones.

Be flexible

Stretch and compress your layouts to accommodate various heights and widths.

Optimize layouts

On larger devices, take advantage of extra screen real estate. Create compound views that combine multiple views to reveal more content and ease navigation.

Assets for all

Provide resources for different screen densities (DPI) to ensure that your app looks great on any device.

Strategies

So where do you begin when designing for multiple screens? One approach is to work in the base standard (normal size and MDPI) and scale it up or down for the other buckets. Another approach is to start with the device with the largest screen size, and then scale down and figure out the UI compromises you'll need to make on smaller screens.

Themes

Gmail in Holo Light.

Settings in Holo Dark.

Talk in Holo Light with dark action bar.

Themes are Android's mechanism for applying a consistent style to an app or activity. The style specifies the visual properties of the elements that make up your user interface, such as color, height, padding and font size. To promote greater cohesion between all apps on the platform, Android provides three system themes that you can choose from when building apps for Ice Cream Sandwich:

• Holo Light
• Holo Dark
• Holo Light with dark action bars

Applying these themes will go a long way in helping you to build apps that fit right into the general visual language of Android.

Pick the system theme that best matches the needs and design aesthetics for your app. If your desire is to have a more distinct look for your app, using one of the system themes as a starting point for your customizations is a good idea. The system themes provide a solid foundation on top of which you can selectively implement your own visual stylings.

Source:http://developer.android.com