NinePatch (or stretchable) images are PNG files that mark the parts of an image that can be stretched. NinePatch images must be properly defined PNG files that end in .9.png. The resource identifier for NinePatches is the file name without the trailing .9.png.
A NinePatch is a variation of a PNG image that uses a one-pixel border to define the area of the image that can be stretched if the image is enlarged. To create a NinePatch, draw single-pixel black lines that represent stretchable areas along the left and top borders of your image. The unmarked sections won't be resized, and the relative size of each of the marked sections will remain the same as the image size changes.
NinePatches are a powerful tool for creating images for the backgrounds of Views or Activities that may have a variable size. For example, Android uses NinePatches to create button borders.
With the first four Android handsets all featuring 3.2'' HVGA screens, it was easy for developers to become complacent when designing their user interfaces. For almost a year after the release of the first Android handset, there was only one screen size and pixel density to design for.
The end of 2009 and start of 2010 heralded an explosion in the number of devices running Android, and with a larger variety of handsets came variation in screen sizes and pixel densities.
It's important to create your UIs knowing that your apps will be running on a broad variety of screen resolutions (including HVGA, QVGA, and two flavors of WVGA — 800x480 and 854x480). Similarly, the physical screen sizes have begun to vary beyond 3.2 inches to include the 3.7-inch Nexus One and Motorola Droid, and the 4-inch Sony Ericsson Xperia X10.
With the floodgates now open, you should expect your applications to be running on an even greater variety of hardware — potentially including tablets, netbooks, and consumer electronics.
The following sections will begin by describing the range of screens you need to consider, and how to support them, before summarizing some of the best practices for ensuring your applications are resolution- and density-independent. Finally, you'll learn how to test your applications against a variety of screen hardware without spending a fortune on phones.
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Quick start guide to skyrocket your offline and online business success with mobile apps. If you know anything about mobile devices, you’ve probably heard that famous phrase coined by one of the mobile device’s most prolific creators proclaiming that there’s an app for pretty much everything.