commit 56b45ed1fae2d4a7cd68c8d38bd61518147bc57e
author Yigit Boyar <yboyar@google.com> Thu Aug 04 16:33:37 2016 -0700
committer Yigit Boyar <yboyar@google.com> Thu Aug 04 23:37:04 2016 +0000
tree c83cea190b63cdafa89b4caa5772264b9a2444b2
parent 48e5d3d43d0e66ee0e6ee2489bf535917523f1a3

RecyclerView scroll callback fix for 0 to 1

This CL fixes a bug in RecyclerView where it would not call
the scroll callbacks if the number of children changed
from 0 to 1 or 1 to 0.

Bug: 29445923
Change-Id: I4ec6fca71ca4800d17b3cc703b8a72b4b180032f

v7/recyclerview/src/android/support/v7/widget/RecyclerView.java

diff --git a/v7/recyclerview/src/android/support/v7/widget/RecyclerView.java b/v7/recyclerview/src/android/support/v7/widget/RecyclerView.java
index afde49c..2c2d587 100644
--- a/v7/recyclerview/src/android/support/v7/widget/RecyclerView.java
+++ b/v7/recyclerview/src/android/support/v7/widget/RecyclerView.java
@@ -3470,8 +3470,8 @@
     private void findMinMaxChildLayoutPositions(int[] into) {
         final int count = mChildHelper.getChildCount();
         if (count == 0) {
-            into[0] = 0;
-            into[1] = 0;
+            into[0] = NO_POSITION;
+            into[1] = NO_POSITION;
             return;
         }
         int minPositionPreLayout = Integer.MAX_VALUE;
@@ -3494,11 +3494,6 @@
     }
 
     private boolean didChildRangeChange(int minPositionPreLayout, int maxPositionPreLayout) {
-        int count = mChildHelper.getChildCount();
-        if (count == 0) {
-            return minPositionPreLayout != 0 || maxPositionPreLayout != 0;
-        }
-        // get the new min max
         findMinMaxChildLayoutPositions(mMinMaxLayoutPositions);
         return mMinMaxLayoutPositions[0] != minPositionPreLayout ||
                 mMinMaxLayoutPositions[1] != maxPositionPreLayout;

v7/recyclerview/tests/src/android/support/v7/widget/RecyclerViewLayoutTest.java

diff --git a/v7/recyclerview/tests/src/android/support/v7/widget/RecyclerViewLayoutTest.java b/v7/recyclerview/tests/src/android/support/v7/widget/RecyclerViewLayoutTest.java
index 665236f..be742d0 100644
--- a/v7/recyclerview/tests/src/android/support/v7/widget/RecyclerViewLayoutTest.java
+++ b/v7/recyclerview/tests/src/android/support/v7/widget/RecyclerViewLayoutTest.java
@@ -967,28 +967,39 @@
     }
 
     @Test
-    public void scrollCalllbackOnVisibleRangeExpand() throws Throwable {
+    public void scrollCallbackFromEmptyToSome() throws Throwable {
+        scrollCallbackOnVisibleRangeChange(1, new int[]{0, 0}, new int[]{0, 1});
+    }
+
+    @Test
+    public void scrollCallbackOnVisibleRangeExpand() throws Throwable {
         scrollCallbackOnVisibleRangeChange(10, new int[]{3, 5}, new int[]{3, 6});
     }
 
     @Test
-    public void scrollCalllbackOnVisibleRangeShrink() throws Throwable {
+    public void scrollCallbackOnVisibleRangeShrink() throws Throwable {
         scrollCallbackOnVisibleRangeChange(10, new int[]{3, 6}, new int[]{3, 5});
     }
 
     @Test
-    public void scrollCalllbackOnVisibleRangeExpand2() throws Throwable {
+    public void scrollCallbackOnVisibleRangeExpand2() throws Throwable {
         scrollCallbackOnVisibleRangeChange(10, new int[]{3, 5}, new int[]{2, 5});
     }
 
     @Test
-    public void scrollCalllbackOnVisibleRangeShrink2() throws Throwable {
+    public void scrollCallbackOnVisibleRangeShrink2() throws Throwable {
         scrollCallbackOnVisibleRangeChange(10, new int[]{3, 6}, new int[]{2, 6});
     }
 
     private void scrollCallbackOnVisibleRangeChange(int itemCount, final int[] beforeRange,
             final int[] afterRange) throws Throwable {
-        RecyclerView recyclerView = new RecyclerView(getActivity());
+        RecyclerView recyclerView = new RecyclerView(getActivity()) {
+            @Override
+            void dispatchLayout() {
+                super.dispatchLayout();
+                ((TestLayoutManager) getLayoutManager()).layoutLatch.countDown();
+            }
+        };
         final AtomicBoolean beforeState = new AtomicBoolean(true);
         TestLayoutManager tlm = new TestLayoutManager() {
             @Override
@@ -996,7 +1007,6 @@
                 detachAndScrapAttachedViews(recycler);
                 int[] range = beforeState.get() ? beforeRange : afterRange;
                 layoutRange(recycler, range[0], range[1]);
-                layoutLatch.countDown();
             }
         };
         recyclerView.setLayoutManager(tlm);