ScaleDrawable

ScaleDrawable is a drawable wrapper in the Android framework that scales its wrapped drawable according to the drawable’s current level. It allows dynamic visual effects such as progress-like filling by adjusting how much of the child drawable is drawn within its bounds. ScaleDrawable belongs to the android.graphics.drawable package and is commonly used to create partial fills, indicators, and other UI elements that change size smoothly.

The scale is controlled by two attributes, scaleWidth and scaleHeight, which define the maximum proportional size of the wrapped drawable along the horizontal and vertical axes. These values are expressed as fractions (for example, 1.0 means 100% of the container, 0.5 means 50%). The current level, which ranges from 0 to 10000, maps to a corresponding scale between 0% and the configured maximum. If useLevel is true (the typical case), the level drives the actual scaling; if set to false, the scale factors are fixed and the level has no effect. Gravity specifies how the scaled child is positioned within the bounds.

XML usage typically looks like a scale tag that references the drawable to wrap and the desired scales, for example: <scale android:drawable="@drawable/foo" android:scaleWidth="100%" android:scaleHeight="100%" android:useLevel="true" android:gravity="center" />. In code, you can instantiate a ScaleDrawable by providing the wrapped drawable, gravity, and the scaleWidth and scaleHeight as fractions.

See also: ClipDrawable, RotateDrawable, LevelListDrawable, Drawable.