Initial state update

ComposeCollapsingTopBar/api/ComposeCollapsingTopBar.klib.api

@@ -194,6 +194,8 @@ final class com.flaringapp.compose.topbar.scaffold/CollapsingTopBarScaffoldScrol
 final class com.flaringapp.compose.topbar.scaffold/CollapsingTopBarScaffoldState : com.flaringapp.compose.topbar.snap/CollapsingTopBarSnapScope, com.flaringapp.compose.topbar/CollapsingTopBarControls { // com.flaringapp.compose.topbar.scaffold/CollapsingTopBarScaffoldState|null[0]
     final val exitState // com.flaringapp.compose.topbar.scaffold/CollapsingTopBarScaffoldState.exitState|{}exitState[0]
         final fun <get-exitState>(): com.flaringapp.compose.topbar.dependent/CollapsingTopBarExitState // com.flaringapp.compose.topbar.scaffold/CollapsingTopBarScaffoldState.exitState.<get-exitState>|<get-exitState>(){}[0]
+    final val hasMeasured // com.flaringapp.compose.topbar.scaffold/CollapsingTopBarScaffoldState.hasMeasured|{}hasMeasured[0]
+        final fun <get-hasMeasured>(): kotlin/Boolean // com.flaringapp.compose.topbar.scaffold/CollapsingTopBarScaffoldState.hasMeasured.<get-hasMeasured>|<get-hasMeasured>(){}[0]
     final val isCollapsed // com.flaringapp.compose.topbar.scaffold/CollapsingTopBarScaffoldState.isCollapsed|{}isCollapsed[0]
         final fun <get-isCollapsed>(): kotlin/Boolean // com.flaringapp.compose.topbar.scaffold/CollapsingTopBarScaffoldState.isCollapsed.<get-isCollapsed>|<get-isCollapsed>(){}[0]
     final val isExpanded // com.flaringapp.compose.topbar.scaffold/CollapsingTopBarScaffoldState.isExpanded|{}isExpanded[0]
@@ -253,6 +255,8 @@ final class com.flaringapp.compose.topbar/CollapsingTopBarLayoutInfo { // com.fl
 final class com.flaringapp.compose.topbar/CollapsingTopBarState : androidx.compose.foundation.gestures/ScrollableState, com.flaringapp.compose.topbar.snap/CollapsingTopBarSnapScope, com.flaringapp.compose.topbar/CollapsingTopBarControls { // com.flaringapp.compose.topbar/CollapsingTopBarState|null[0]
     constructor <init>(kotlin/Boolean = ...) // com.flaringapp.compose.topbar/CollapsingTopBarState.<init>|<init>(kotlin.Boolean){}[0]
 
+    final val hasMeasured // com.flaringapp.compose.topbar/CollapsingTopBarState.hasMeasured|{}hasMeasured[0]
+        final fun <get-hasMeasured>(): kotlin/Boolean // com.flaringapp.compose.topbar/CollapsingTopBarState.hasMeasured.<get-hasMeasured>|<get-hasMeasured>(){}[0]
     final val isCollapsed // com.flaringapp.compose.topbar/CollapsingTopBarState.isCollapsed|{}isCollapsed[0]
         final fun <get-isCollapsed>(): kotlin/Boolean // com.flaringapp.compose.topbar/CollapsingTopBarState.isCollapsed.<get-isCollapsed>|<get-isCollapsed>(){}[0]
     final val isExpanded // com.flaringapp.compose.topbar/CollapsingTopBarState.isExpanded|{}isExpanded[0]

ComposeCollapsingTopBar/src/commonMain/kotlin/com/flaringapp/compose/topbar/CollapsingTopBar.kt

@@ -54,7 +54,8 @@ import kotlin.math.roundToInt
  * Each child may actively participate in collapsing process with [CollapsingTopBarScope] modifiers.
  *
  * Advanced collapsing techniques can be achieved using:
- * - transformations based on [CollapsingTopBarState.layoutInfo]
+ * - transformations based on [CollapsingTopBarState.layoutInfo]. When exact bounds matter, use
+ * [CollapsingTopBarState.hasMeasured] to distinguish placeholder values from actual measurements.
  * - custom layout logic with [CollapsingTopBarNestedCollapseElement]
  *
  * @param modifier the [Modifier] to be applied to this top bar.

ComposeCollapsingTopBar/src/commonMain/kotlin/com/flaringapp/compose/topbar/CollapsingTopBarState.kt

@@ -29,6 +29,7 @@ import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.saveable.Saver
 import androidx.compose.runtime.saveable.rememberSaveable
+import androidx.compose.runtime.setValue
 import androidx.compose.runtime.snapshots.Snapshot
 import com.flaringapp.compose.topbar.snap.CollapsingTopBarSnapScope
 import kotlin.math.max
@@ -91,9 +92,25 @@ public class CollapsingTopBarState @RememberInComposition internal constructor(
         layoutInfo.isExpanded
     }
 
+    /**
+     * Whether this state has received actual layout measurements from [CollapsingTopBar].
+     *
+     * Before the first measurement pass, [layoutInfo] contains placeholder values that are safe
+     * for arithmetic but do not yet represent real measured bounds.
+     */
+    public val hasMeasured: Boolean
+        get() = hasMeasuredState
+
+    private var hasMeasuredState by mutableStateOf(false)
+
     /**
      * The layout info object calculated during the last layout pass.
      *
+     * Before [hasMeasured] becomes true, this property contains placeholder values rather than
+     * actual measured bounds. These placeholders are intentionally non-zero to remain safe for
+     * arithmetic such as division, but consumers should check [hasMeasured] when exact
+     * measurements are required.
+     *
      * Note that this property is observable and is updated after every scroll or remeasure.
      * If you use it in the composable function it will be recomposed on every change causing
      * potential performance issues including infinity recomposition loop.
@@ -204,6 +221,7 @@ public class CollapsingTopBarState @RememberInComposition internal constructor(
             collapsedHeight = collapsedHeight,
             expandedHeight = expandedHeight,
         ).also {
+            hasMeasuredState = true
             layoutInfoState.value = it
         }
     }

ComposeCollapsingTopBar/src/commonMain/kotlin/com/flaringapp/compose/topbar/scaffold/CollapsingTopBarScaffoldState.kt

@@ -69,13 +69,6 @@ public class CollapsingTopBarScaffoldState @RememberInComposition internal const
 ) : CollapsingTopBarControls,
     CollapsingTopBarSnapScope {
 
-    /**
-     * The current visual top bar height, either during collapse or exit.
-     */
-    @get:FrequentlyChangingValue
-    public val totalTopBarHeight: Float
-        get() = topBarState.layoutInfo.height - exitState.exitHeight
-
     /**
      * Whether top bar is fully expanded and entered.
      */
@@ -91,6 +84,22 @@ public class CollapsingTopBarScaffoldState @RememberInComposition internal const
             (!exitState.isEnabled || exitState.isFullyExited)
     }
 
+    /**
+     * Whether [topBarState] has received actual layout measurements.
+     */
+    public val hasMeasured: Boolean
+        get() = topBarState.hasMeasured
+
+    /**
+     * The current visual top bar height, either during collapse or exit.
+     *
+     * Before [hasMeasured] becomes true, this property is based on placeholder layout values
+     * rather than actual measured bounds.
+     */
+    @get:FrequentlyChangingValue
+    public val totalTopBarHeight: Float
+        get() = topBarState.layoutInfo.height - exitState.exitHeight
+
     override suspend fun expand(animationSpec: AnimationSpec<Float>) {
         animateHeightTo(animationSpec) {
             topBarState.layoutInfo.expandedHeight.toFloat()

README.md

@@ -585,8 +585,13 @@ Contains information about the collapsing state up until top bar starts exiting
 mode supports that). Offers state data similar to scaffold: `state.isExpanded` and
 `state.isCollapsed`, as well as manual controls: `state.expand()` and `state.collapse()`.
 
-This state exposes comprehensive measurement data via `layoutInfo`, such as collapse progress
-`layoutInfo.collapseProgress`, collapsed height `layoutInfo.collapsedHeight` etc.
+This state also exposes `hasMeasured` to indicate whether the top bar has already received
+actual layout measurements.
+
+Comprehensive measurement data is available via `layoutInfo`, such as collapse progress
+`layoutInfo.collapseProgress`, collapsed height `layoutInfo.collapsedHeight` etc. Before
+`hasMeasured` becomes true, `layoutInfo` contains safe placeholder values rather than actual
+measured bounds.
 
 </details>