[This post is by Scott Main, lead tech writer for developer.android.com. — Tim Bray]

Android tablets are becoming more popular, and we're pleased to note that the vast majority of apps resize to the larger screens just fine. To keep the few apps that don't resize well from frustrating users with awkward-looking apps on their tablets, Android 3.2 introduces a screen compatibility mode that makes these apps more usable on tablets. If your app is one of the many that do resize well, however, you should update your app as soon as possible to disable screen compatibility mode so that users experience your app the way you intend.

Beginning with Android 3.2, any app that does not target Android 3.0 (set either android:minSdkVersion or android:targetSdkVersion to “11” or higher) or does not explicitly set android:xlargeScreens="true" in the <supports-screens> element will include a button in the system bar that, when touched, allows users to select between two viewing modes on large-screen devices.

“Stretch to fill screen” is normal layout resizing (using your app’s alternative resources for size and density) and “Zoom to fill screen” is the new screen compatibility mode.

When the user enables this screen compatibility mode, the system no longer resizes your layout to fit the screen. Instead, it runs your app in an emulated normal/mdpi screen (approximately 320dp x 480dp) and scales that up to fill the screen---imagine viewing your app at the size of a phone screen then zooming in about 200%. The effect is that everything is bigger, but also more pixelated, because the system does not resize your layout or use your alternative resources for the current device (the system uses all resources for a normal/mdpi device). Here’s a comparison of what it looks like (screen compatibility mode enabled on the right):

In cases where an app does not properly resize for larger screens, this screen compatibility mode can improve the app’s usability by emulating the app’s phone-style look, but zoomed in to fill the screen on a tablet.

However, most apps (even those that don’t specifically target Honeycomb) look just fine on tablets without screen compatibility mode, due to the use of alternative layouts for different screen sizes and the framework’s flexibility when resizing layouts. Unfortunately, if you haven’t said so in your manifest file, the system doesn’t know that your application properly supports large screens. Thus, if you’ve developed your app against any version lower than Android 3.0 and do not declare support for large screens in your manifest, the system is going to offer users the option to enable screen compatibility mode.

So, if your app is actually designed to resize for large screens, screen compatibility mode is probably an inferior user experience for your app and you should prevent users from using it. The easiest way to make sure that users cannot enable screen compatibility mode for your app is to declare support for xlarge screens in your manifest file’s <supports-screens> element. For example:

<manifest ... > <supports-screens android:xlargeScreens="true" /> ... </manifest>

That’s it! No more screen compatibility mode.

Note: If your app is specifically designed to support Android 3.0 and declares either android:minSdkVersion or android:targetSdkVersion with a value of “11” or greater, then your app is already in the clear and screen compatibility mode will not be offered to users, but adding this attribute certainly won’t hurt.

In conclusion, if your app has set the android:minSdkVersion and android:targetSdkVersion both with values less than “11” and you believe your app works well on large and xlarge screens (for example, you’ve tested on a Honeycomb tablet), you should make the above addition to your manifest file in order to disable the new screen compatibility mode.

If your app does not resize properly for large screens, then users might better enjoy your app using screen compatibility mode. However, please follow our guide to Supporting Multiple Screens so that you can also disable screen compatibility mode and provide a user experience that’s optimized for large-screen devices.