diff --git a/src/com/android/launcher3/widget/WidgetListRowEntry.java b/src/com/android/launcher3/widget/WidgetListRowEntry.java
index 3e89eeb..335b8c7 100644
--- a/src/com/android/launcher3/widget/WidgetListRowEntry.java
+++ b/src/com/android/launcher3/widget/WidgetListRowEntry.java
@@ -41,4 +41,8 @@
         this.widgets = items;
     }
 
+    @Override
+    public String toString() {
+        return pkgItem.packageName + ":" + widgets.size();
+    }
 }
diff --git a/src/com/android/launcher3/widget/WidgetsContainerView.java b/src/com/android/launcher3/widget/WidgetsContainerView.java
index 14a9d17..acec3dd 100644
--- a/src/com/android/launcher3/widget/WidgetsContainerView.java
+++ b/src/com/android/launcher3/widget/WidgetsContainerView.java
@@ -17,10 +17,12 @@
 package com.android.launcher3.widget;
 
 import android.content.Context;
+import android.content.pm.LauncherApps;
 import android.graphics.Point;
 import android.support.v7.widget.LinearLayoutManager;
 import android.util.AttributeSet;
 import android.util.Log;
+import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.Toast;
@@ -31,8 +33,10 @@
 import com.android.launcher3.DropTarget.DragObject;
 import com.android.launcher3.ItemInfo;
 import com.android.launcher3.Launcher;
+import com.android.launcher3.LauncherAppState;
 import com.android.launcher3.R;
 import com.android.launcher3.Utilities;
+import com.android.launcher3.compat.AlphabeticIndexCompat;
 import com.android.launcher3.dragndrop.DragOptions;
 import com.android.launcher3.folder.Folder;
 import com.android.launcher3.model.PackageItemInfo;
@@ -74,7 +78,11 @@
     public WidgetsContainerView(Context context, AttributeSet attrs, int defStyleAttr) {
         super(context, attrs, defStyleAttr);
         mLauncher = Launcher.getLauncher(context);
-        mAdapter = new WidgetsListAdapter(this, this, context);
+        LauncherAppState apps = LauncherAppState.getInstance(context);
+        mAdapter = new WidgetsListAdapter(context, LayoutInflater.from(context),
+                apps.getWidgetCache(), new AlphabeticIndexCompat(context), this, this,
+                new WidgetsDiffReporter(apps.getIconCache()));
+        mAdapter.setNotifyListener();
         if (LOGD) {
             Log.d(TAG, "WidgetsContainerView constructor");
         }
@@ -232,7 +240,6 @@
      */
     public void setWidgets(MultiHashMap<PackageItemInfo, WidgetItem> model) {
         mAdapter.setWidgets(model);
-        mAdapter.notifyDataSetChanged();
 
         View loader = getContentView().findViewById(R.id.loader);
         if (loader != null) {
diff --git a/src/com/android/launcher3/widget/WidgetsDiffReporter.java b/src/com/android/launcher3/widget/WidgetsDiffReporter.java
new file mode 100644
index 0000000..d9c9ef9
--- /dev/null
+++ b/src/com/android/launcher3/widget/WidgetsDiffReporter.java
@@ -0,0 +1,140 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.launcher3.widget;
+
+import android.util.Log;
+
+import com.android.launcher3.IconCache;
+import com.android.launcher3.model.PackageItemInfo;
+import com.android.launcher3.widget.WidgetsListAdapter.WidgetListRowEntryComparator;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+
+/**
+ * Do diff on widget's tray list items and call the {@link NotifyListener} methods accordingly.
+ */
+public class WidgetsDiffReporter {
+    private final boolean DEBUG = true;
+    private final String TAG = "WidgetsDiffReporter";
+    private final IconCache mIconCache;
+    private NotifyListener mListener;
+
+    public interface NotifyListener {
+        void notifyDataSetChanged();
+        void notifyItemChanged(int index);
+        void notifyItemInserted(int index);
+        void notifyItemRemoved(int index);
+    }
+
+    public WidgetsDiffReporter(IconCache iconCache) {
+        mIconCache = iconCache;
+    }
+
+    public void setListener(NotifyListener listener) {
+        mListener = listener;
+    }
+
+    public void process(ArrayList<WidgetListRowEntry> currentEntries,
+            ArrayList<WidgetListRowEntry> newEntries, WidgetListRowEntryComparator comparator) {
+        if (DEBUG) {
+            Log.d(TAG, "process oldEntries#=" + currentEntries.size()
+                    + " newEntries#=" + newEntries.size());
+        }
+        if (currentEntries.size() == 0 && newEntries.size() > 0) {
+            currentEntries.addAll(newEntries);
+            mListener.notifyDataSetChanged();
+            return;
+        }
+        ArrayList<WidgetListRowEntry> orgEntries =
+                (ArrayList<WidgetListRowEntry>) currentEntries.clone();
+        Iterator<WidgetListRowEntry> orgIter = orgEntries.iterator();
+        Iterator<WidgetListRowEntry> newIter = newEntries.iterator();
+
+        WidgetListRowEntry orgRowEntry = orgIter.next();
+        WidgetListRowEntry newRowEntry = newIter.next();
+
+        do {
+            int diff = comparePackageName(orgRowEntry, newRowEntry, comparator);
+            if (DEBUG) {
+                Log.d(TAG, String.format("diff=%d orgRowEntry (%s) newRowEntry (%s)",
+                        diff, orgRowEntry != null? orgRowEntry.toString() : null,
+                        newRowEntry != null? newRowEntry.toString() : null));
+            }
+            int index = -1;
+            if (diff < 0) {
+                index = currentEntries.indexOf(orgRowEntry);
+                mListener.notifyItemRemoved(index);
+                if (DEBUG) {
+                    Log.d(TAG, String.format("notifyItemRemoved called (%d)%s", index,
+                            orgRowEntry.titleSectionName));
+                }
+                currentEntries.remove(index);
+                orgRowEntry = orgIter.hasNext() ? orgIter.next() : null;
+            } else if (diff > 0) {
+                index = orgRowEntry != null? currentEntries.indexOf(orgRowEntry):
+                        currentEntries.size();
+                currentEntries.add(index, newRowEntry);
+                newRowEntry = newIter.hasNext() ? newIter.next() : null;
+                mListener.notifyItemInserted(index);
+                if (DEBUG) {
+                    Log.d(TAG, String.format("notifyItemInserted called (%d)%s", index,
+                            newRowEntry.titleSectionName));
+                }
+            } else {
+                // same package name but,
+                // did the icon, title, etc, change?
+                // or did the widget size and desc, span, etc change?
+                if (!isSamePackageItemInfo(orgRowEntry.pkgItem, newRowEntry.pkgItem) ||
+                        !orgRowEntry.widgets.equals(newRowEntry.widgets)) {
+                    index = currentEntries.indexOf(orgRowEntry);
+                    currentEntries.set(index, newRowEntry);
+                    mListener.notifyItemChanged(index);
+                    if (DEBUG) {
+                        Log.d(TAG, String.format("notifyItemChanged called (%d)%s", index,
+                                newRowEntry.titleSectionName));
+                    }
+                }
+                orgRowEntry = orgIter.hasNext() ? orgIter.next() : null;
+                newRowEntry = newIter.hasNext() ? newIter.next() : null;
+            }
+        } while(orgRowEntry != null || newRowEntry != null);
+    }
+
+    /**
+     * Compare package name using the same comparator as in {@link WidgetsListAdapter}.
+     * Also handle null row pointers.
+     */
+    private int comparePackageName(WidgetListRowEntry curRow, WidgetListRowEntry newRow,
+            WidgetListRowEntryComparator comparator) {
+        if (curRow == null && newRow == null) {
+            throw new IllegalStateException("Cannot compare PackageItemInfo if both rows are null.");
+        }
+
+        if (curRow == null && newRow != null) {
+            return 1; // new row needs to be inserted
+        } else if (curRow != null && newRow == null) {
+            return -1; // old row needs to be deleted
+        }
+        return comparator.compare(curRow, newRow);
+    }
+
+    private boolean isSamePackageItemInfo(PackageItemInfo curInfo, PackageItemInfo newInfo) {
+        return curInfo.iconBitmap.equals(newInfo.iconBitmap) &&
+                !mIconCache.isDefaultIcon(curInfo.iconBitmap, curInfo.user);
+    }
+}
diff --git a/src/com/android/launcher3/widget/WidgetsListAdapter.java b/src/com/android/launcher3/widget/WidgetsListAdapter.java
index a1eb0ab..6b1800c 100644
--- a/src/com/android/launcher3/widget/WidgetsListAdapter.java
+++ b/src/com/android/launcher3/widget/WidgetsListAdapter.java
@@ -21,9 +21,10 @@
 import android.util.Log;
 import android.view.LayoutInflater;
 import android.view.View;
+import android.view.View.OnClickListener;
+import android.view.View.OnLongClickListener;
 import android.view.ViewGroup;
 
-import com.android.launcher3.LauncherAppState;
 import com.android.launcher3.R;
 import com.android.launcher3.WidgetPreviewLoader;
 import com.android.launcher3.compat.AlphabeticIndexCompat;
@@ -55,40 +56,67 @@
 
     private final WidgetPreviewLoader mWidgetPreviewLoader;
     private final LayoutInflater mLayoutInflater;
-
-    private final View.OnClickListener mIconClickListener;
-    private final View.OnLongClickListener mIconLongClickListener;
-
-    private final ArrayList<WidgetListRowEntry> mEntries = new ArrayList<>();
     private final AlphabeticIndexCompat mIndexer;
 
+    private final OnClickListener mIconClickListener;
+    private final OnLongClickListener mIconLongClickListener;
     private final int mIndent;
+    private ArrayList<WidgetListRowEntry> mEntries = new ArrayList<>();
+    private final WidgetsDiffReporter mDiffReporter;
 
-    public WidgetsListAdapter(View.OnClickListener iconClickListener,
-            View.OnLongClickListener iconLongClickListener,
-            Context context) {
-        mLayoutInflater = LayoutInflater.from(context);
-        mWidgetPreviewLoader = LauncherAppState.getInstance(context).getWidgetCache();
-
-        mIndexer = new AlphabeticIndexCompat(context);
-
+    public WidgetsListAdapter(Context context, LayoutInflater layoutInflater,
+            WidgetPreviewLoader widgetPreviewLoader, AlphabeticIndexCompat indexCompat,
+            OnClickListener iconClickListener, OnLongClickListener iconLongClickListener,
+            WidgetsDiffReporter diffReporter) {
+        mLayoutInflater = layoutInflater;
+        mWidgetPreviewLoader = widgetPreviewLoader;
+        mIndexer = indexCompat;
         mIconClickListener = iconClickListener;
         mIconLongClickListener = iconLongClickListener;
         mIndent = context.getResources().getDimensionPixelSize(R.dimen.widget_section_indent);
+        mDiffReporter = diffReporter;
     }
 
-    public void setWidgets(MultiHashMap<PackageItemInfo, WidgetItem> widgets) {
-        mEntries.clear();
-        WidgetItemComparator widgetComparator = new WidgetItemComparator();
+    public void setNotifyListener() {
+        mDiffReporter.setListener(new WidgetsDiffReporter.NotifyListener() {
+            @Override
+            public void notifyDataSetChanged() {
+                WidgetsListAdapter.this.notifyDataSetChanged();
+            }
 
+            @Override
+            public void notifyItemChanged(int index) {
+                WidgetsListAdapter.this.notifyItemChanged(index);
+            }
+
+            @Override
+            public void notifyItemInserted(int index) {
+                WidgetsListAdapter.this.notifyItemInserted(index);
+            }
+
+            @Override
+            public void notifyItemRemoved(int index) {
+                WidgetsListAdapter.this.notifyItemRemoved(index);
+            }
+        });
+    }
+
+    /**
+     * Update the widget list.
+     */
+    public void setWidgets(MultiHashMap<PackageItemInfo, WidgetItem> widgets) {
+        ArrayList<WidgetListRowEntry> tempEntries = new ArrayList<>();
+
+        WidgetItemComparator widgetComparator = new WidgetItemComparator();
         for (Map.Entry<PackageItemInfo, ArrayList<WidgetItem>> entry : widgets.entrySet()) {
             WidgetListRowEntry row = new WidgetListRowEntry(entry.getKey(), entry.getValue());
             row.titleSectionName = mIndexer.computeSectionName(row.pkgItem.title);
             Collections.sort(row.widgets, widgetComparator);
-            mEntries.add(row);
+            tempEntries.add(row);
         }
-
-        Collections.sort(mEntries, new WidgetListRowEntryComparator());
+        WidgetListRowEntryComparator rowComparator = new WidgetListRowEntryComparator();
+        Collections.sort(tempEntries, rowComparator);
+        mDiffReporter.process(mEntries, tempEntries, rowComparator);
     }
 
     @Override
diff --git a/tests/src/com/android/launcher3/widget/WidgetsListAdapterTest.java b/tests/src/com/android/launcher3/widget/WidgetsListAdapterTest.java
new file mode 100644
index 0000000..40b65e4
--- /dev/null
+++ b/tests/src/com/android/launcher3/widget/WidgetsListAdapterTest.java
@@ -0,0 +1,149 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.android.launcher3.widget;
+
+import android.appwidget.AppWidgetProviderInfo;
+import android.content.Context;
+import android.content.pm.PackageManager;
+import android.graphics.Bitmap;
+import android.support.test.InstrumentationRegistry;
+import android.support.test.filters.SmallTest;
+import android.support.test.runner.AndroidJUnit4;
+import android.view.LayoutInflater;
+
+import com.android.launcher3.IconCache;
+import com.android.launcher3.InvariantDeviceProfile;
+import com.android.launcher3.LauncherAppWidgetProviderInfo;
+import com.android.launcher3.WidgetPreviewLoader;
+import com.android.launcher3.compat.AlphabeticIndexCompat;
+import com.android.launcher3.compat.AppWidgetManagerCompat;
+import com.android.launcher3.model.PackageItemInfo;
+import com.android.launcher3.model.WidgetItem;
+import com.android.launcher3.util.MultiHashMap;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+import static org.mockito.Matchers.any;
+import static org.mockito.Matchers.anyInt;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+
+@SmallTest
+@RunWith(AndroidJUnit4.class)
+public class WidgetsListAdapterTest {
+
+    private final String TAG = "WidgetsListAdapterTest";
+
+    @Mock private LayoutInflater mMockLayoutInflater;
+    @Mock private WidgetPreviewLoader mMockWidgetCache;
+    @Mock private WidgetsDiffReporter.NotifyListener mListener;
+    @Mock private IconCache mIconCache;
+
+    private WidgetsListAdapter mAdapter;
+    private AlphabeticIndexCompat mIndexCompat;
+    private InvariantDeviceProfile mTestProfile;
+    private Context mContext;
+
+    @Before
+    public void setup() {
+        MockitoAnnotations.initMocks(this);
+        mContext = InstrumentationRegistry.getTargetContext();
+        mTestProfile = new InvariantDeviceProfile();
+        mTestProfile.numRows = 5;
+        mTestProfile.numColumns = 5;
+        mIndexCompat = new AlphabeticIndexCompat(mContext);
+        WidgetsDiffReporter reporter = new WidgetsDiffReporter(mIconCache);
+        reporter.setListener(mListener);
+        mAdapter = new WidgetsListAdapter(mContext, mMockLayoutInflater, mMockWidgetCache,
+                mIndexCompat, null, null, reporter);
+    }
+
+    @Test
+    public void test_notifyDataSetChanged() throws Exception {
+        mAdapter.setWidgets(generateSampleMap(1));
+        verify(mListener, times(1)).notifyDataSetChanged();
+    }
+
+    @Test
+    public void test_notifyItemInserted() throws Exception {
+        mAdapter.setWidgets(generateSampleMap(1));
+        mAdapter.setWidgets(generateSampleMap(2));
+        verify(mListener, times(1)).notifyDataSetChanged();
+        verify(mListener, times(1)).notifyItemInserted(1);
+    }
+
+    @Test
+    public void test_notifyItemRemoved() throws Exception {
+        mAdapter.setWidgets(generateSampleMap(2));
+        mAdapter.setWidgets(generateSampleMap(1));
+        verify(mListener, times(1)).notifyDataSetChanged();
+        verify(mListener, times(1)).notifyItemRemoved(1);
+    }
+
+    @Test
+    public void testNotifyItemChanged_PackageIconDiff() throws Exception {
+        mAdapter.setWidgets(generateSampleMap(1));
+        mAdapter.setWidgets(generateSampleMap(1));
+        verify(mListener, times(1)).notifyDataSetChanged();
+        verify(mListener, times(1)).notifyItemChanged(0);
+    }
+
+    @Test
+    public void testNotifyItemChanged_widgetItemInfoDiff() throws Exception {
+        // TODO: same package name but item number changed
+    }
+
+    @Test
+    public void testNotifyItemInsertedRemoved_hodgepodge() throws Exception {
+        // TODO: insert and remove combined.          curMap
+        // newMap [A, C, D]                           [A, B, E]
+        // B - C < 0, removed B from index 1          [A, E]
+        // E - C > 0, C inserted to index 1           [A, C, E]
+        // E - D > 0, D inserted to index 2           [A, C, D, E]
+        // E - null = -1, E deleted from index 3      [A, C, D]
+    }
+
+    /**
+     * Helper method to generate the sample widget model map that can be used for the tests
+     * @param num the number of WidgetItem the map should contain
+     * @return
+     */
+    private MultiHashMap<PackageItemInfo, WidgetItem> generateSampleMap(int num) {
+        MultiHashMap<PackageItemInfo, WidgetItem> newMap = new MultiHashMap();
+        if (num <= 0) return newMap;
+
+        PackageManager pm = mContext.getPackageManager();
+        AppWidgetManagerCompat widgetManager = AppWidgetManagerCompat.getInstance(mContext);
+        for (AppWidgetProviderInfo widgetInfo : widgetManager.getAllProviders(null)) {
+            WidgetItem wi = new WidgetItem(LauncherAppWidgetProviderInfo
+                    .fromProviderInfo(mContext, widgetInfo), pm, mTestProfile);
+
+            PackageItemInfo pInfo = new PackageItemInfo(wi.componentName.getPackageName());
+            pInfo.title = pInfo.packageName;
+            pInfo.user = wi.user;
+            pInfo.iconBitmap = Bitmap.createBitmap(10, 10, Bitmap.Config.ALPHA_8);
+            newMap.addToList(pInfo, wi);
+            if (newMap.size() == num) {
+                break;
+            }
+        }
+        return newMap;
+    }
+}