android: fix custom top bar title Fill alignment

android/src/main/java/com/reactnativenavigation/views/stack/topbar/titlebar/TitleAndButtonsContainer.kt

@@ -106,6 +106,7 @@ class TitleAndButtonsContainer(context: Context) : ViewGroup(context) {
     override fun onLayout(changed: Boolean, l: Int, t: Int, r: Int, b: Int) {
         val titleComponent = getTitleComponent()
         val isCenter = titleComponentAlignment == Alignment.Center
+        val isFill = titleComponentAlignment == Alignment.Fill
         val containerWidth = r - l
         val containerHeight = b - t
         val isRTL = isRTL()
@@ -114,7 +115,7 @@ class TitleAndButtonsContainer(context: Context) : ViewGroup(context) {
         val leftBarWidth = leftButtonBar.measuredWidth
         val rightBarWidth = rightButtonBar.measuredWidth
 
-        val (titleLeft, titleRight) = resolveHorizontalTitleBoundsLimit(containerWidth, titleWidth, leftBarWidth, rightBarWidth, isCenter, isRTL)
+        val (titleLeft, titleRight) = resolveHorizontalTitleBoundsLimit(containerWidth, titleWidth, leftBarWidth, rightBarWidth, isCenter, isRTL, isFill)
         val (titleTop, titleBottom) = resolveVerticalTitleBoundsLimit(containerHeight, titleHeight)
         val (leftButtonsLeft, leftButtonsRight) = resolveLeftButtonsBounds(containerWidth, leftBarWidth, isRTL)
         val (rightButtonsLeft, rightButtonsRight) = resolveRightButtonsBounds(containerWidth, rightButtonBar.measuredWidth, isRTL)

android/src/main/java/com/reactnativenavigation/views/stack/topbar/titlebar/TitleAndButtonsMeasurer.kt

@@ -19,12 +19,14 @@ fun makeTitleAtMostWidthMeasureSpec(containerWidth: Int, rightBarWidth: Int, lef
     return if (isCenter) {
         val availableWidth = containerWidth - rightBarWidth - leftBarWidth
         View.MeasureSpec.makeMeasureSpec(availableWidth, View.MeasureSpec.AT_MOST)
+    } else if (isFill) {
+        // Fill alignment must span the entire space between left and right button bars,
+        // so do not reserve the DEFAULT_LEFT_MARGIN_PX padding used for left-aligned titles.
+        val availableWidth = containerWidth - rightBarWidth - leftBarWidth
+        View.MeasureSpec.makeMeasureSpec(availableWidth, View.MeasureSpec.EXACTLY)
     } else {
         val availableWidth = containerWidth - rightBarWidth - leftBarWidth - 2 * DEFAULT_LEFT_MARGIN_PX
-        View.MeasureSpec.makeMeasureSpec(
-            availableWidth,
-            if (isFill) View.MeasureSpec.EXACTLY else View.MeasureSpec.AT_MOST
-        )
+        View.MeasureSpec.makeMeasureSpec(availableWidth, View.MeasureSpec.AT_MOST)
     }
 }
 
@@ -41,14 +43,22 @@ fun resolveHorizontalTitleBoundsLimit(
         leftBarWidth: Int,
         rightBarWidth: Int,
         isCenter: Boolean,
-        isRTL: Boolean
+        isRTL: Boolean,
+        isFill: Boolean = false
 ): Pair<TitleLeft, TitleRight> {
     val resolvedLeftBarWidth = if (isRTL) rightBarWidth else leftBarWidth
     val resolvedRightBarWidth = if (isRTL) leftBarWidth else rightBarWidth
     var suggestedLeft: TitleLeft
     var suggestedRight: TitleRight
 
     val rightLimit = parentWidth - resolvedRightBarWidth
+    if (isFill) {
+        // Fill alignment must span the entire space between the left and right
+        // button bars without the DEFAULT_LEFT_MARGIN_PX reservation used for
+        // left-aligned titles. Mirrors the measure spec produced by
+        // makeTitleAtMostWidthMeasureSpec when isFill = true.
+        return resolvedLeftBarWidth to rightLimit
+    }
     if (isCenter) {
         val availableSpace = parentWidth - resolvedLeftBarWidth - resolvedRightBarWidth
         if (titleWidth >= availableSpace) {

android/src/test/java/com/reactnativenavigation/utils/TitleAndButtonsMeasurer.kt

@@ -1,7 +1,9 @@
 package com.reactnativenavigation.utils
 
+import android.view.View
 import com.reactnativenavigation.BaseRobolectricTest
 import com.reactnativenavigation.views.stack.topbar.titlebar.DEFAULT_LEFT_MARGIN_PX
+import com.reactnativenavigation.views.stack.topbar.titlebar.makeTitleAtMostWidthMeasureSpec
 import com.reactnativenavigation.views.stack.topbar.titlebar.resolveHorizontalTitleBoundsLimit
 import com.reactnativenavigation.views.stack.topbar.titlebar.resolveLeftButtonsBounds
 import com.reactnativenavigation.views.stack.topbar.titlebar.resolveRightButtonsBounds
@@ -355,4 +357,82 @@ class TitleAndButtonsMeasurer : BaseRobolectricTest() {
         assertEquals(parentWidth - leftButtons - DEFAULT_LEFT_MARGIN_PX - barWidth - DEFAULT_LEFT_MARGIN_PX, left)
         assertEquals(parentWidth - leftButtons - DEFAULT_LEFT_MARGIN_PX, right)
     }
-}
+
+    // ----- makeTitleAtMostWidthMeasureSpec -----
+
+    @Test
+    fun `makeTitleAtMostWidthMeasureSpec - Fill - no buttons - EXACTLY full container width`() {
+        val spec = makeTitleAtMostWidthMeasureSpec(parentWidth, 0, 0, isCenter = false, isFill = true)
+        assertEquals(View.MeasureSpec.EXACTLY, View.MeasureSpec.getMode(spec))
+        assertEquals(parentWidth, View.MeasureSpec.getSize(spec))
+    }
+
+    @Test
+    fun `makeTitleAtMostWidthMeasureSpec - Fill - with buttons - EXACTLY width minus bars`() {
+        val leftBar = 120
+        val rightBar = 80
+        val spec = makeTitleAtMostWidthMeasureSpec(parentWidth, rightBar, leftBar, isCenter = false, isFill = true)
+        assertEquals(View.MeasureSpec.EXACTLY, View.MeasureSpec.getMode(spec))
+        assertEquals(parentWidth - leftBar - rightBar, View.MeasureSpec.getSize(spec))
+    }
+
+    @Test
+    fun `makeTitleAtMostWidthMeasureSpec - Center - AT_MOST full container width minus bars`() {
+        val leftBar = 100
+        val rightBar = 100
+        val spec = makeTitleAtMostWidthMeasureSpec(parentWidth, rightBar, leftBar, isCenter = true)
+        assertEquals(View.MeasureSpec.AT_MOST, View.MeasureSpec.getMode(spec))
+        assertEquals(parentWidth - leftBar - rightBar, View.MeasureSpec.getSize(spec))
+    }
+
+    @Test
+    fun `makeTitleAtMostWidthMeasureSpec - default (left-aligned) - keeps 2 x DEFAULT_LEFT_MARGIN_PX reservation`() {
+        val leftBar = 100
+        val rightBar = 100
+        val spec = makeTitleAtMostWidthMeasureSpec(parentWidth, rightBar, leftBar, isCenter = false, isFill = false)
+        assertEquals(View.MeasureSpec.AT_MOST, View.MeasureSpec.getMode(spec))
+        assertEquals(parentWidth - leftBar - rightBar - 2 * DEFAULT_LEFT_MARGIN_PX, View.MeasureSpec.getSize(spec))
+    }
+
+    // ----- resolveHorizontalTitleBoundsLimit - Fill alignment -----
+
+    @Test
+    fun `Fill - no buttons - Title should span full container width`() {
+        val barWidth = 200 // measured width of the title component
+        val leftButtons = 0
+        val rightButtons = 0
+        val isRTL = false
+        val center = false
+        val isFill = true
+        val (left, right) = resolveHorizontalTitleBoundsLimit(parentWidth, barWidth, leftButtons, rightButtons, center, isRTL, isFill)
+        assertEquals(0, left)
+        assertEquals(parentWidth, right)
+    }
+
+    @Test
+    fun `Fill - with buttons - Title should span between buttons without DEFAULT_LEFT_MARGIN_PX`() {
+        val barWidth = 200
+        val leftButtons = 120
+        val rightButtons = 80
+        val isRTL = false
+        val center = false
+        val isFill = true
+        val (left, right) = resolveHorizontalTitleBoundsLimit(parentWidth, barWidth, leftButtons, rightButtons, center, isRTL, isFill)
+        assertEquals(leftButtons, left)
+        assertEquals(parentWidth - rightButtons, right)
+    }
+
+    @Test
+    fun `RTL - Fill - with buttons - Title should span between buttons after RTL flip`() {
+        val barWidth = 200
+        val leftButtons = 120
+        val rightButtons = 80
+        val isRTL = true
+        val center = false
+        val isFill = true
+        val (left, right) = resolveHorizontalTitleBoundsLimit(parentWidth, barWidth, leftButtons, rightButtons, center, isRTL, isFill)
+        // RTL flips logical left/right: leftButtons render on the right edge, rightButtons on the left.
+        assertEquals(rightButtons, left)
+        assertEquals(parentWidth - leftButtons, right)
+    }
+}

android/src/test/java/com/reactnativenavigation/views/TitleAndButtonsContainerTest.kt

@@ -352,8 +352,11 @@ class TitleAndButtonsContainerTest : BaseTest() {
         )
         component = uut.getTitleComponent()
         idleMainLooper()
-        assertThat(component.left).isEqualTo(DEFAULT_LEFT_MARGIN_PX)
-        assertThat(component.right).isEqualTo(titleBarWidth + 2 * DEFAULT_LEFT_MARGIN_PX)
+        // Fill alignment must span the full container width between left and right
+        // button bars (zero-width here). The previous assertion that allowed the
+        // DEFAULT_LEFT_MARGIN_PX reservation matched left-aligned behaviour, not Fill.
+        assertThat(component.left).isEqualTo(0)
+        assertThat(component.right).isEqualTo(UUT_WIDTH)
     }
 
     @Test