Window Size Classes

Window Size Classes

A window size class buckets the space your window actually has, not the device's screen, so a tablet in split screen can be compact. Width is what usually decides the layout:

Width size classes and where they occur
Width class	Window width	Typical device
Compact	under 600 dp	phone in portrait
Medium	600 to 839 dp	tablet or unfolded foldable in portrait
Expanded	840 to 1199 dp	tablet in landscape, phone in landscape
Large and Extra-large	1200 dp and up	desktop windows, large tablets

currentWindowAdaptiveInfoV2() returns the class as State, recomputed on rotation, resize and fold, so the composables that read it recompose (the older currentWindowAdaptiveInfo() is deprecated in adaptive 1.3.0, with a compiler warning to use V2 "to support L and XL width size classes"). Compare with breakpoints, never with exact sizes:

ui/AdaptiveCatalog.kt: logging the width class and the postureKotlin

@Composable
fun LogWindowInfo() {
  val info = currentWindowAdaptiveInfoV2()               // recomputed on every window change
  val size = info.windowSizeClass
  val width = when {
    size.isWidthAtLeastBreakpoint(WindowSizeClass.WIDTH_DP_LARGE_LOWER_BOUND) -> "LARGE"
    size.isWidthAtLeastBreakpoint(WindowSizeClass.WIDTH_DP_EXPANDED_LOWER_BOUND) -> "EXPANDED"
    size.isWidthAtLeastBreakpoint(WindowSizeClass.WIDTH_DP_MEDIUM_LOWER_BOUND) -> "MEDIUM"
    else -> "COMPACT"
  }
  SideEffect {
    Log.d(TAG, "width $width (>= ${size.minWidthDp} dp), posture ${info.windowPosture}")
    Log.d(TAG, "mode: ${postureMode(info.windowPosture)}")
  }
}

Logged in portrait, after rotating to landscape, and after rotating back:

Output of 105

D/BookNestAdaptive: width COMPACT (>= 0 dp), posture Posture(isTabletop=false, hinges=[])
D/BookNestAdaptive: mode: flat: no separating hinge
D/BookNestAdaptive: width EXPANDED (>= 840 dp), posture Posture(isTabletop=false, hinges=[])
D/BookNestAdaptive: mode: flat: no separating hinge
D/BookNestAdaptive: width COMPACT (>= 0 dp), posture Posture(isTabletop=false, hinges=[])
D/BookNestAdaptive: mode: flat: no separating hinge

minWidthDp is the class's lower bound, not the window's width. Height classes (compact under 480 dp, medium to 899, expanded above) matter for landscape phones, where a tall layout may not fit.

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