From e99a31fdd3336e638ae3444fccc81c7340c8f932 Mon Sep 17 00:00:00 2001
From: Ruben Sousa <ruben@rubensousa.com>
Date: Wed, 21 Aug 2024 18:51:51 +0200
Subject: [PATCH] Fix header not keeping the same anchor

---
 .../tests/layout/DpadScrollableLayoutTest.kt  | 55 +++++++++++--------
 .../dpadrecyclerview_scrollable_container.xml | 46 +++++++++-------
 .../dpadrecyclerview/DpadScrollableLayout.kt  | 25 +++++++--
 3 files changed, 79 insertions(+), 47 deletions(-)

diff --git a/dpadrecyclerview/src/androidTest/kotlin/com/rubensousa/dpadrecyclerview/test/tests/layout/DpadScrollableLayoutTest.kt b/dpadrecyclerview/src/androidTest/kotlin/com/rubensousa/dpadrecyclerview/test/tests/layout/DpadScrollableLayoutTest.kt
index b5453ea3..e5b8146d 100644
--- a/dpadrecyclerview/src/androidTest/kotlin/com/rubensousa/dpadrecyclerview/test/tests/layout/DpadScrollableLayoutTest.kt
+++ b/dpadrecyclerview/src/androidTest/kotlin/com/rubensousa/dpadrecyclerview/test/tests/layout/DpadScrollableLayoutTest.kt
@@ -19,6 +19,7 @@ package com.rubensousa.dpadrecyclerview.test.tests.layout
 import android.graphics.Rect
 import android.os.Bundle
 import android.view.View
+import android.view.ViewGroup
 import androidx.core.view.updateLayoutParams
 import androidx.fragment.app.Fragment
 import androidx.fragment.app.testing.FragmentScenario
@@ -87,6 +88,23 @@ class DpadScrollableLayoutTest {
         )
     }
 
+    @Test
+    fun testHeaderStartsCompletelyVisible() {
+        val headerBounds = getViewBounds(R.id.headerLayout)
+        assertThat(headerBounds.top).isEqualTo(0)
+
+        var completelyVisible = false
+        var visible = false
+
+        fragmentScenario.onFragment { fragment ->
+            completelyVisible = fragment.scrollableLayout!!.isHeaderCompletelyVisible
+            visible = fragment.scrollableLayout!!.isHeaderVisible
+        }
+
+        assertThat(completelyVisible).isTrue()
+        assertThat(visible).isTrue()
+    }
+
     @Test
     fun testHidingHeaderWithoutAnimation() {
         // given
@@ -259,13 +277,13 @@ class DpadScrollableLayoutTest {
 
         // when
         fragmentScenario.onFragment { fragment ->
-            fragment.scrollableLayout?.removeViewAt(0)
+            fragment.scrollableLayout?.findViewById<ViewGroup>(R.id.headerLayout)?.removeViewAt(0)
         }
 
         // then
-        val header2Bounds = getViewBounds(R.id.header2)
+        val headerBounds = getViewBounds(R.id.headerLayout)
         val recyclerViewBounds = getViewBounds(R.id.recyclerView)
-        assertThat(header2Bounds).isEqualTo(
+        assertThat(headerBounds).isEqualTo(
             Rect(0, -headerHeight, screenWidth, 0)
         )
         assertThat(recyclerViewBounds).isEqualTo(
@@ -286,13 +304,13 @@ class DpadScrollableLayoutTest {
 
         // when
         fragmentScenario.onFragment { fragment ->
-            fragment.scrollableLayout?.removeViewAt(0)
+            fragment.scrollableLayout?.findViewById<ViewGroup>(R.id.headerLayout)?.removeViewAt(0)
         }
 
         // then
-        val header2Bounds = getViewBounds(R.id.header2)
+        val headerBounds = getViewBounds(R.id.headerLayout)
         val recyclerViewBounds = getViewBounds(R.id.recyclerView)
-        assertThat(header2Bounds).isEqualTo(
+        assertThat(headerBounds).isEqualTo(
             Rect(0, 0, screenWidth, headerHeight)
         )
         assertThat(recyclerViewBounds).isEqualTo(
@@ -313,7 +331,7 @@ class DpadScrollableLayoutTest {
 
         // when
         fragmentScenario.onFragment { fragment ->
-            fragment.header1?.updateLayoutParams<DpadScrollableLayout.LayoutParams> {
+            fragment.header1?.updateLayoutParams {
                 height *= 2
             }
         }
@@ -334,36 +352,25 @@ class DpadScrollableLayoutTest {
     }
 
     @Test
-    fun testOffsetIsAdjustedWhenLayoutGetsBiggerWhileHeaderIsVisible() {
+    fun testBottomStaysAlignedWhenHeaderGrowsWhileVisible() {
         // given
         val headerHeight = getHeaderHeight()
-        val screenWidth = getWidth()
-        val screenHeight = getHeight()
         fragmentScenario.onFragment { fragment ->
             fragment.scrollableLayout?.scrollHeaderTo(topOffset = -headerHeight / 2)
         }
         waitViewAtCoordinates(R.id.header1, top = -headerHeight / 2, bottom = headerHeight / 2)
+        val headerBounds = getViewBounds(R.id.headerLayout)
 
         // when
         fragmentScenario.onFragment { fragment ->
-            fragment.header1?.updateLayoutParams<DpadScrollableLayout.LayoutParams> {
+            fragment.header1?.updateLayoutParams {
                 height *= 2
             }
         }
 
         // then
-        val header1Bounds = getViewBounds(R.id.header1)
-        val header2Bounds = getViewBounds(R.id.header2)
-        val recyclerViewBounds = getViewBounds(R.id.recyclerView)
-        assertThat(header1Bounds).isEqualTo(
-            Rect(0, 0, screenWidth, headerHeight * 2)
-        )
-        assertThat(header2Bounds).isEqualTo(
-            Rect(0, headerHeight * 2, screenWidth, headerHeight * 3)
-        )
-        assertThat(recyclerViewBounds).isEqualTo(
-            Rect(0, headerHeight * 3, screenWidth, screenHeight + headerHeight * 3)
-        )
+        val newBounds = getViewBounds(R.id.headerLayout)
+        assertThat(newBounds.bottom).isEqualTo(headerBounds.bottom)
     }
 
     @Test
@@ -384,7 +391,7 @@ class DpadScrollableLayoutTest {
         // then
         val header1Bounds = getViewBounds(R.id.header1)
         assertThat(header1Bounds).isEqualTo(
-            Rect(0,  -headerHeight / 2, screenWidth, headerHeight / 2)
+            Rect(0, -headerHeight / 2, screenWidth, headerHeight / 2)
         )
     }
 
diff --git a/dpadrecyclerview/src/androidTest/res/layout/dpadrecyclerview_scrollable_container.xml b/dpadrecyclerview/src/androidTest/res/layout/dpadrecyclerview_scrollable_container.xml
index 490eddac..9cd3a381 100644
--- a/dpadrecyclerview/src/androidTest/res/layout/dpadrecyclerview_scrollable_container.xml
+++ b/dpadrecyclerview/src/androidTest/res/layout/dpadrecyclerview_scrollable_container.xml
@@ -5,27 +5,35 @@
     android:layout_width="match_parent"
     android:layout_height="match_parent">
 
-    <TextView
-        android:id="@+id/header1"
+    <LinearLayout
+        android:id="@+id/headerLayout"
         android:layout_width="match_parent"
-        android:layout_height="@dimen/dpadrecyclerview_header_size"
-        android:background="@drawable/dpadrecyclerview_item_background"
-        android:focusable="true"
-        android:focusableInTouchMode="true"
-        android:gravity="center"
-        android:text="Header 1"
-        android:textColor="@color/dpadrecyclerview_item_text" />
+        android:layout_height="wrap_content"
+        android:orientation="vertical">
 
-    <TextView
-        android:id="@+id/header2"
-        android:layout_width="match_parent"
-        android:layout_height="@dimen/dpadrecyclerview_header_size"
-        android:background="@drawable/dpadrecyclerview_item_background"
-        android:focusable="true"
-        android:focusableInTouchMode="true"
-        android:gravity="center"
-        android:text="Header 2"
-        android:textColor="@color/dpadrecyclerview_item_text" />
+        <TextView
+            android:id="@+id/header1"
+            android:layout_width="match_parent"
+            android:layout_height="@dimen/dpadrecyclerview_header_size"
+            android:background="@drawable/dpadrecyclerview_item_background"
+            android:focusable="true"
+            android:focusableInTouchMode="true"
+            android:gravity="center"
+            android:text="Header 1"
+            android:textColor="@color/dpadrecyclerview_item_text" />
+
+        <TextView
+            android:id="@+id/header2"
+            android:layout_width="match_parent"
+            android:layout_height="@dimen/dpadrecyclerview_header_size"
+            android:background="@drawable/dpadrecyclerview_item_background"
+            android:focusable="true"
+            android:focusableInTouchMode="true"
+            android:gravity="center"
+            android:text="Header 2"
+            android:textColor="@color/dpadrecyclerview_item_text" />
+
+    </LinearLayout>
 
     <com.rubensousa.dpadrecyclerview.DpadRecyclerView
         android:id="@+id/recyclerView"
diff --git a/dpadrecyclerview/src/main/java/com/rubensousa/dpadrecyclerview/DpadScrollableLayout.kt b/dpadrecyclerview/src/main/java/com/rubensousa/dpadrecyclerview/DpadScrollableLayout.kt
index cc0b13bc..db965152 100644
--- a/dpadrecyclerview/src/main/java/com/rubensousa/dpadrecyclerview/DpadScrollableLayout.kt
+++ b/dpadrecyclerview/src/main/java/com/rubensousa/dpadrecyclerview/DpadScrollableLayout.kt
@@ -46,7 +46,7 @@ import kotlin.math.min
  * To show it back again, use [showHeader]
  */
 class DpadScrollableLayout @JvmOverloads constructor(
-    context: Context, attrs: AttributeSet? = null
+    context: Context, attrs: AttributeSet? = null,
 ) : LinearLayout(context, attrs) {
 
     var headerHeight = 0
@@ -55,10 +55,14 @@ class DpadScrollableLayout @JvmOverloads constructor(
     var isHeaderVisible = true
         private set
 
+    var isHeaderCompletelyVisible = true
+        private set
+
     private var currentOffset = 0
     private var offsetInProgress: Int? = null
     private var currentAnimator: ScrollAnimator? = null
     private var headerHeightChanged = false
+    private var lastHeaderHeight = 0
     private var scrollDurationConfig: ScrollDurationConfig = DefaultScrollDurationConfig()
 
     // From RecyclerView
@@ -114,6 +118,7 @@ class DpadScrollableLayout @JvmOverloads constructor(
         }
         setMeasuredDimension(measuredWidth, childHeight)
         headerHeightChanged = newHeaderHeight != headerHeight
+        lastHeaderHeight = headerHeight
         headerHeight = newHeaderHeight
     }
 
@@ -122,7 +127,7 @@ class DpadScrollableLayout @JvmOverloads constructor(
         parentWidthMeasureSpec: Int,
         widthUsed: Int,
         parentHeightMeasureSpec: Int,
-        heightUsed: Int
+        heightUsed: Int,
     ) {
         val lp = child!!.layoutParams as LayoutParams
         val childWidthMeasureSpec = getChildMeasureSpec(
@@ -149,13 +154,24 @@ class DpadScrollableLayout @JvmOverloads constructor(
     }
 
     override fun onLayout(changed: Boolean, l: Int, t: Int, r: Int, b: Int) {
-        var currentAnchor = if (currentOffset != -headerHeight && headerHeightChanged) {
-            if (isHeaderVisible) {
+        var currentAnchor = if (headerHeightChanged) {
+            if (isHeaderCompletelyVisible) {
+                // If the header was completely visible before, keep it that way
                 0
+            } else if (isHeaderVisible) {
+                /**
+                 * The header was partially visible, so keep the anchor consistent if possible,
+                 * and limit it to the top of the layout
+                 */
+                val currentHeaderBottom = currentOffset + lastHeaderHeight
+                val newTop = currentHeaderBottom - headerHeight
+                min(0, newTop)
             } else {
+                // The header was completely invisible, so ensure it stays that way
                 -headerHeight
             }
         } else {
+            // The height didn't change, so keep the previous offset
             currentOffset
         }
         val numberOfChildren = childCount
@@ -254,6 +270,7 @@ class DpadScrollableLayout @JvmOverloads constructor(
         }
         currentOffset = getChildAt(0)?.top ?: 0
         isHeaderVisible = currentOffset > -headerHeight
+        isHeaderCompletelyVisible = currentOffset == 0
     }
 
     private fun cancelOffsetAnimation() {