NinePatchDrawable

NinePatchDrawable is a type of drawable used in the Android framework to render and scale bitmap images defined as nine-patch assets. A nine-patch image is a PNG file whose name ends with .9.png and includes a one-pixel border that encodes how the image can be stretched and where content should be placed. The top and left borders mark stretchable areas, while the bottom and right borders specify the content padding. This enables the central region to stretch while the corners and edges retain their shape, ensuring UI elements such as buttons and panels scale cleanly across different sizes and screen densities.

As a subclass of Drawable, NinePatchDrawable renders a bitmap according to the patch information and handles padding, transparency, and state changes. It preserves the visual integrity of corners and edges while permitting the middle area to resize to fit the view’s bounds. The drawable can be tinted, filtered, and used in standard view backgrounds or as part of more complex drawable compositions. It participates in the Android state system, so it can adapt its appearance in response to pressed, focused, or disabled states when defined in a stateful resource.

Creation and usage typically involve providing a properly prepared .9.png asset located in the app’s resources (for example, res/drawable). Tools such as the Draw 9-patch editor are used during asset creation to define stretchable regions and padding. NinePatchDrawable is commonly used for backgrounds and other scalable UI components, offering a robust solution for maintaining visual fidelity across layouts and densities.

See also: Drawable, NinePatch, 9-patch creation tools, ShapeDrawable, VectorDrawable.