Issue #288 Use hasSameContentAs for comparing Item equality

library/src/main/java/com/xwray/groupie/DiffCallback.java

@@ -39,7 +39,7 @@ public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
     public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
         Item oldItem = GroupUtils.getItem(oldGroups, oldItemPosition);
         Item newItem = GroupUtils.getItem(newGroups, newItemPosition);
-        return newItem.equals(oldItem);
+        return newItem.hasSameContentAs(oldItem);
     }
 
     @Nullable

library/src/main/java/com/xwray/groupie/Item.java

@@ -188,6 +188,8 @@ public long getId() {
      * even if there has been a change in that data.
      * <p>
      * The default implementation compares both view type and id.
+     *
+     * @return True if the items are the same, false otherwise.
      */
     public boolean isSameAs(Item other) {
         if (getViewType() != other.getViewType()) {
@@ -196,6 +198,20 @@ public boolean isSameAs(Item other) {
         return getId() == other.getId();
     }
 
+    /**
+     * Whether this item has the same content as another when compared using DiffUtil.
+     *
+     * After two items have been determined to be the same using {@link #isSameAs(Item)} this function
+     * should check whether their contents are the same.
+     *
+     * The default implementation does this using {@link #equals(Object)}
+     *
+     * @return True if both items have the same content, false otherwise
+     */
+    public boolean hasSameContentAs(Item other) {
+        return this.equals(other);
+    }
+
     @Nullable
     public Object getChangePayload(Item newItem) {
         return null;

library/src/main/java/com/xwray/groupie/Section.java

@@ -132,9 +132,9 @@ public void clear() {
      * <p>
      * Item comparisons are made using:
      * - Item.isSameAs(Item otherItem) (are items the same?)
-     * - Item.equals() (are contents the same?)
+     * - Item.hasSameContentAs() (are contents the same?)
      * <p>
-     * If you don't customize getId() or isSameAs() and equals(), the default implementations will return false,
+     * If you don't customize getId() or isSameAs() and hasSameContentAs(), the default implementations will return false,
      * meaning your Group will consider every update a complete change of everything.
      *
      * This will default detectMoves to true.
@@ -152,9 +152,9 @@ public void update(@NonNull final Collection<? extends Group> newBodyGroups) {
      * <p>
      * Item comparisons are made using:
      * - Item.isSameAs(Item otherItem) (are items the same?)
-     * - Item.equals() (are contents the same?)
+     * - Item.hasSameContentAs() (are contents the same?)
      * <p>
-     * If you don't customize getId() or isSameAs() and equals(), the default implementations will return false,
+     * If you don't customize getId() or isSameAs() and hasSameContentAs(), the default implementations will return false,
      * meaning your Group will consider every update a complete change of everything.
      *
      * @param newBodyGroups The new content of the section

library/src/main/java/com/xwray/groupie/UpdatingGroup.java

@@ -16,8 +16,8 @@
  * <p>
  * Item comparisons are made using:
  * - Item.getId() (are items the same?)
- * - Item.equals() (are contents the same?)
- * If you don't customize getId() or equals(), the default implementations will return false,
+ * - Item.hasSameContentAs() (are contents the same?)
+ * If you don't customize getId() or hasSameContentAs(), the default implementations will return false,
  * meaning your Group will consider every update a complete change of everything.
  */
 @Deprecated
@@ -108,7 +108,7 @@ public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
         public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
             Item oldItem = items.get(oldItemPosition);
             Item newItem = newList.get(newItemPosition);
-            return oldItem.equals(newItem);
+            return oldItem.hasSameContentAs(newItem);
         }
     }
 }

library/src/test/java/com/xwray/groupie/ItemTest.java

@@ -1,12 +1,17 @@
 package com.xwray.groupie;
 
-import junit.framework.Assert;
+import androidx.annotation.NonNull;
 
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.Mock;
-import org.mockito.runners.MockitoJUnitRunner;
+import org.mockito.junit.MockitoJUnitRunner;
 
+import java.util.Objects;
+
+import static junit.framework.TestCase.assertEquals;
+import static junit.framework.TestCase.assertFalse;
+import static junit.framework.TestCase.assertTrue;
 import static org.mockito.Mockito.verify;
 
 @RunWith(MockitoJUnitRunner.class)
@@ -16,16 +21,16 @@ public class ItemTest {
     GroupAdapter groupAdapter;
 
     @Test
-    public void selfPositionIs0() throws Exception {
+    public void selfPositionIs0() {
         Item item = new DummyItem();
-        Assert.assertEquals(0, item.getPosition(item));
+        assertEquals(0, item.getPosition(item));
     }
 
     @Test
-    public void positionIsNegative1IfItemIsNotSelf() throws Exception {
+    public void positionIsNegative1IfItemIsNotSelf() {
         Item item = new DummyItem();
         Item differentItem = new DummyItem();
-        Assert.assertEquals(-1, item.getPosition(differentItem));
+        assertEquals(-1, item.getPosition(differentItem));
     }
 
     @Test
@@ -36,4 +41,73 @@ public void notifyChangeNotifiesParentObserver() {
 
         verify(groupAdapter).onItemChanged(item, 0);
     }
+
+    @Test
+    public void isSameAsFailsIfViewTypeIsDifferent() {
+        final DataItem itemA = new DataItem(0, 1, 0);
+        final DataItem itemB = new DataItem(1, 1, 0);
+
+        assertFalse(itemA.isSameAs(itemB));
+    }
+
+    @Test
+    public void isSameAsSucceedsIfIdMatches() {
+        final DataItem itemA = new DataItem(1, 1, 0);
+        final DataItem itemB = new DataItem(1, 1, 0);
+        final DataItem itemC = new DataItem(1, 2, 0);
+
+        assertTrue(itemA.isSameAs(itemB));
+        assertFalse(itemA.isSameAs(itemC));
+    }
+
+    @Test
+    public void hasSameContentAsUsesEqualsByDefault() {
+        final DataItem itemA = new DataItem(0, 1, 2);
+        final DataItem itemB = new DataItem(0, 1, 2);
+        final DataItem itemC = new DataItem(0, 1, 3);
+
+        assertTrue(itemA.hasSameContentAs(itemB));
+        assertFalse(itemA.hasSameContentAs(itemC));
+    }
+
+    private static class DataItem extends Item {
+
+        private int layout;
+        private long id;
+        private int equalsComparison;
+
+        DataItem(int layout, long id, int equalsComparison) {
+            this.layout = layout;
+            this.id = id;
+            this.equalsComparison = equalsComparison;
+        }
+
+        @Override
+        public void bind(@NonNull ViewHolder viewHolder, int position) {
+
+        }
+
+        @Override
+        public long getId() {
+            return id;
+        }
+
+        @Override
+        public int getLayout() {
+            return layout;
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) return true;
+            if (o == null || getClass() != o.getClass()) return false;
+            DataItem dataItem = (DataItem) o;
+            return equalsComparison == dataItem.equalsComparison;
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(equalsComparison);
+        }
+    }
 }