StateListDrawable

StateListDrawable is an Android drawable subclass that manages a limited set of drawable resources keyed by view states. It is commonly used to provide different visual representations for UI components such as buttons, checkboxes, and list items depending on their current state (pressed, focused, selected, enabled, etc.). The drawable map is defined in an XML file located in the res/drawable directory, using the <selector> element to list each <item> with a state specification. When the Android framework renders a view, it queries the StateListDrawable for the drawable that matches the view’s current state set and displays it.

The state list can reference other drawables (bitmaps, shape XMLs, or color resources) as well as nine-patch images, gradients, or LayerDrawable combinations. StateListDrawable supports complex combinations of states, allowing developers to craft nuanced visual feedback. It also provides a default fallback drawable (an item without a state attribute) for states that do not have an explicit match.

To use a StateListDrawable, a developer can assign it to a view’s background attribute in XML or set it programmatically via setBackground or setBackgroundDrawable. External libraries and custom view components often expose their own state lists, simplifying the creation of highly responsive UI elements. StateListDrawable has existed since the early days of Android (API level 1) and remains the primary mechanism for state-dependent drawables in the framework.