The main principle of responsive mobile design is to adapt the presentation of the content to the current context. Let’s take a look at the redesigned item details page in the latest release of Android Market client (shown here are Galaxy Nexus, Iconia A100 and Xoom):

In order to take advantage of the available screen estate, the layout and styling of different elements differ between the various size ranges (with two switching points at 600dp and 800dp). The thumbnail becomes progressively larger, application title and developer name are displayed with different foreground colors, the rating stars move from the byline section into the summary section in left column and the overall styling of the top banner is different.

Having three different layout definitions for the same page can result in a lot of duplicate resources and Java code. To prevent this from happening, we strive to follow these two guidelines:

• Use include and merge tags to extract common pieces of layouts for reusal. For example, all three layouts above have the same inner layout for screenshots, +1 and description sections (and many others not shown here). Having a single definition means less maintenance and simpler bug fixes.
• Use the same android:id values for elements that display the specific content, even if they are located in different parts of your layouts. For example, the text views that show the application title and developer name live in layouts that are not reused across the different representations – due to different target designs. However, the Java code that populates the values does not have to be aware of the layout differences. Using the same android:id means that you can use View.findViewById() API and confine the differences to XML files only.

Support for multiple presentation buckets is implemented with the resource selectors introduced in Android 3.2. Earlier implementations of large screen support in Android Market client used the -w resource selector, switching to two column representation of the details page at 1000dp (depending on the specific page). A new, more compact layout for the two-column representation allows us to switch as early as 800dp, with an additional switching point at 600dp to take advantage of the available width for better layout of the summary section. Instead of using -w600dp and -w800dp, we use a combination of -w and -h. Here is why.

When you identify the target layout (in our case two-column layout with different scrolling points in the columns), when you identify where does each piece of your content go, where you create the visual language for styling the content and finalize the pixel-perfect metrics – this is when you identify how much space do you need at minimum to switch to that representation. Knowing the complexity and density of the content, and knowing the visual styling of the building blocks you then decide what is the specific value where switching to the different representation not only allows the user to complete the target flows in a much more comfortable fashion, but also results in a balanced and pleasing visual appearance.

Using -w selector only ignores the restrictions imposed by non-scrollable content. In the 600dp-800dp range, the summary section is taller and remains locked. If we use this representation on a device with, say, 600*300dp viewable area, the scrolling content will take an uncomfortably small screen area. In the 800dp+ range that displays two column view, the colored banned area is even taller and remains locked as well (with action buttons in left column snapping). The same scrolling considerations apply here as well. And so, in addition to using -w selector, we “augment” it with -h:

• layout/details.xml for the default size bucket
• layout-w600dp-h540dp for the medium size bucket
• layout-w800dp-h540dp for the large size bucket
• values-w1000dp-h540dp for some additional value for extra large size bucket

A few things to note.

• The current most common hardware configuration for 7″ tablets is 1024*600dp. In landscape mode, the position of the system status bar means that applications have less than 600dp height available to them. If your target switching point is around 1024dp (and our two-column layout switching point is 800dp), the value for -h should take this into consideration. Note that things may change in the future, and the set of best practices will follow.
• Once you start using the new resource selectors, you should get familiar with the rules for finding the best-match resource.
• For example, -sw600dp will “win” over -w800dp, -w800dp-h540dp or -w1000dp even for landscape Xoom (which is 1280*800 without the system bar). This means that if you want to use a combination of -w and -h, you should use them in all folders, even when the values are the same and you think that -sw is just a shortcut. It’s not.
• As another example, -w800dp-h540dp will “win” over -w1000dp even for landscape Xoom. This is the reason to have -w1000dp-h540dp in our current implementation.

Stay tuned for more in the coming months as we continue refining and polishing the application across the entire gamut of supported devices.