perf: diff root list updates by stable item keys

android/app/src/test/java/com/hyzq/boss/MainActivityRootListAdapterTest.java

@@ -0,0 +1,87 @@
+package com.hyzq.boss;
+
+import static org.junit.Assert.assertEquals;
+
+import android.view.View;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.RuntimeEnvironment;
+import org.robolectric.annotation.Config;
+
+import java.util.List;
+
+import androidx.recyclerview.widget.RecyclerView;
+
+@RunWith(RobolectricTestRunner.class)
+@Config(sdk = 34)
+public class MainActivityRootListAdapterTest {
+    @Test
+    public void submitUsesItemDiffInsteadOfFullDatasetChange() {
+        MainActivity.RootListAdapter adapter = new MainActivity.RootListAdapter();
+        RecordingObserver observer = new RecordingObserver();
+        adapter.registerAdapterDataObserver(observer);
+
+        adapter.submit(List.of(
+                fakeItem("conversation:a", "same"),
+                fakeItem("conversation:b", "before")
+        ));
+        observer.reset();
+
+        adapter.submit(List.of(
+                fakeItem("conversation:a", "same"),
+                fakeItem("conversation:b", "after")
+        ));
+
+        assertEquals(0, observer.changedAllCount);
+        assertEquals(1, observer.itemRangeChangedCount);
+        assertEquals(1, observer.lastChangedPosition);
+        assertEquals(1, observer.lastChangedCount);
+    }
+
+    private static MainActivity.RootListItem fakeItem(String key, String signature) {
+        return new MainActivity.RootListItem() {
+            @Override
+            public String stableKey() {
+                return key;
+            }
+
+            @Override
+            public String contentSignature() {
+                return signature;
+            }
+
+            @Override
+            public View build() {
+                return new View(RuntimeEnvironment.getApplication());
+            }
+        };
+    }
+
+    private static final class RecordingObserver extends RecyclerView.AdapterDataObserver {
+        int changedAllCount;
+        int itemRangeChangedCount;
+        int lastChangedPosition = -1;
+        int lastChangedCount = -1;
+
+        void reset() {
+            changedAllCount = 0;
+            itemRangeChangedCount = 0;
+            lastChangedPosition = -1;
+            lastChangedCount = -1;
+        }
+
+        @Override
+        public void onChanged() {
+            changedAllCount += 1;
+        }
+
+        @Override
+        public void onItemRangeChanged(int positionStart, int itemCount) {
+            itemRangeChangedCount += 1;
+            lastChangedPosition = positionStart;
+            lastChangedCount = itemCount;
+        }
+    }
+}