diff --git a/java/src/com/android/inputmethod/keyboard/MainKeyboardView.java b/java/src/com/android/inputmethod/keyboard/MainKeyboardView.java
index c6c7315..4c73da9 100644
--- a/java/src/com/android/inputmethod/keyboard/MainKeyboardView.java
+++ b/java/src/com/android/inputmethod/keyboard/MainKeyboardView.java
@@ -64,6 +64,7 @@
 import java.util.WeakHashMap;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 /**
  * A view that is responsible for detecting key presses and touch movements.
@@ -306,17 +307,24 @@
         animatorToStart.setCurrentPlayTime(startTime);
     }
 
-    // Implements {@link TimerHander.Callbacks} method.
+    // Implements {@link TimerHander.Callbacks#startWhileTypingAnimation(int)}.
+    /**
+     * Called when a while-typing-animation should be started.
+     * @param fadeInOrOut {@link TimerHandler.Callbacks#FADE_IN} starts while-typing-fade-in
+     * animation. {@link TimerHandler.Callbacks#FADE_OUT} starts while-typing-fade-out animation.
+     */
     @Override
-    public void startWhileTypingFadeinAnimation() {
-        cancelAndStartAnimators(
-                mAltCodeKeyWhileTypingFadeoutAnimator, mAltCodeKeyWhileTypingFadeinAnimator);
-    }
-
-    @Override
-    public void startWhileTypingFadeoutAnimation() {
-        cancelAndStartAnimators(
-                mAltCodeKeyWhileTypingFadeinAnimator, mAltCodeKeyWhileTypingFadeoutAnimator);
+    public void startWhileTypingAnimation(final int fadeInOrOut) {
+        switch (fadeInOrOut) {
+        case TimerHandler.Callbacks.FADE_IN:
+            cancelAndStartAnimators(
+                    mAltCodeKeyWhileTypingFadeoutAnimator, mAltCodeKeyWhileTypingFadeinAnimator);
+            break;
+        case TimerHandler.Callbacks.FADE_OUT:
+            cancelAndStartAnimators(
+                    mAltCodeKeyWhileTypingFadeinAnimator, mAltCodeKeyWhileTypingFadeoutAnimator);
+            break;
+        }
     }
 
     @ExternallyReferenced
@@ -474,7 +482,7 @@
 
     // Implements {@link TimerHandler.Callbacks#dismissKeyPreviewWithoutDelay(Key)}.
     @Override
-    public void dismissKeyPreviewWithoutDelay(final Key key) {
+    public void dismissKeyPreviewWithoutDelay(@Nonnull final Key key) {
         mKeyPreviewChoreographer.dismissKeyPreview(key, false /* withAnimation */);
         invalidateKey(key);
     }
@@ -496,12 +504,11 @@
     @Override
     public void showSlidingKeyInputPreview(final PointerTracker tracker) {
         locatePreviewPlacerView();
-        mSlidingKeyInputDrawingPreview.setPreviewPosition(tracker);
-    }
-
-    @Override
-    public void dismissSlidingKeyInputPreview() {
-        mSlidingKeyInputDrawingPreview.dismissSlidingKeyInputPreview();
+        if (tracker != null) {
+            mSlidingKeyInputDrawingPreview.setPreviewPosition(tracker);
+        } else {
+            mSlidingKeyInputDrawingPreview.dismissSlidingKeyInputPreview();
+        }
     }
 
     private void setGesturePreviewMode(final boolean isGestureTrailEnabled,
@@ -596,13 +603,13 @@
         return moreKeysKeyboardView;
     }
 
-    // Implements {@link TimerHandler.Callbacks} method.
+    // Implements {@link TimerHandler.Callbacks#onLongPress(PointerTracker)}.
     /**
      * Called when a key is long pressed.
      * @param tracker the pointer tracker which pressed the parent key
      */
     @Override
-    public void onLongPress(final PointerTracker tracker) {
+    public void onLongPress(@Nonnull final PointerTracker tracker) {
         if (isShowingMoreKeysPanel()) {
             return;
         }
@@ -674,8 +681,8 @@
         onDismissMoreKeysPanel();
         // Dismiss all key previews that may be being showed.
         PointerTracker.setReleasedKeyGraphicsToAllKeys();
-        // Dismiss  sliding key input preview that may be being showed.
-        dismissSlidingKeyInputPreview();
+        // Dismiss sliding key input preview that may be being showed.
+        mSlidingKeyInputDrawingPreview.dismissSlidingKeyInputPreview();
         panel.showInParent(mDrawingPreviewPlacerView);
         mMoreKeysPanel = panel;
     }
@@ -744,7 +751,7 @@
         mTimerHandler.cancelAllMessages();
         PointerTracker.setReleasedKeyGraphicsToAllKeys();
         mGestureFloatingTextDrawingPreview.dismissGestureFloatingPreviewText();
-        dismissSlidingKeyInputPreview();
+        mSlidingKeyInputDrawingPreview.dismissSlidingKeyInputPreview();
         PointerTracker.dismissAllMoreKeysPanels();
         PointerTracker.cancelAllPointerTrackers();
     }
diff --git a/java/src/com/android/inputmethod/keyboard/PointerTracker.java b/java/src/com/android/inputmethod/keyboard/PointerTracker.java
index 5a540ff..fcf0522 100644
--- a/java/src/com/android/inputmethod/keyboard/PointerTracker.java
+++ b/java/src/com/android/inputmethod/keyboard/PointerTracker.java
@@ -41,6 +41,9 @@
 
 import java.util.ArrayList;
 
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
 public final class PointerTracker implements PointerTrackerQueue.Element,
         BatchInputArbiterListener {
     private static final String TAG = PointerTracker.class.getSimpleName();
@@ -53,9 +56,9 @@
         public void invalidateKey(Key key);
         public void showKeyPreview(Key key);
         public void dismissKeyPreview(Key key);
-        public void showSlidingKeyInputPreview(PointerTracker tracker);
-        public void dismissSlidingKeyInputPreview();
-        public void showGestureTrail(PointerTracker tracker, boolean showsFloatingPreviewText);
+        public void showSlidingKeyInputPreview(@Nullable PointerTracker tracker);
+        public void showGestureTrail(@Nonnull PointerTracker tracker,
+                boolean showsFloatingPreviewText);
     }
 
     public interface TimerProxy {
@@ -416,6 +419,7 @@
         return mIsInDraggingFinger;
     }
 
+    @Nullable
     public Key getKey() {
         return mCurrentKey;
     }
@@ -765,7 +769,7 @@
     private void resetKeySelectionByDraggingFinger() {
         mIsInDraggingFinger = false;
         mIsInSlidingKeyInput = false;
-        sDrawingProxy.dismissSlidingKeyInputPreview();
+        sDrawingProxy.showSlidingKeyInputPreview(null /* tracker */);
     }
 
     private void onGestureMoveEvent(final int x, final int y, final long eventTime,
diff --git a/java/src/com/android/inputmethod/keyboard/internal/AbstractDrawingPreview.java b/java/src/com/android/inputmethod/keyboard/internal/AbstractDrawingPreview.java
index 755a99a..c76a9ac 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/AbstractDrawingPreview.java
+++ b/java/src/com/android/inputmethod/keyboard/internal/AbstractDrawingPreview.java
@@ -22,6 +22,8 @@
 import com.android.inputmethod.keyboard.MainKeyboardView;
 import com.android.inputmethod.keyboard.PointerTracker;
 
+import javax.annotation.Nonnull;
+
 /**
  * Abstract base class for previews that are drawn on DrawingPreviewPlacerView, e.g.,
  * GestureFloatingTextDrawingPreview, GestureTrailsDrawingPreview, and
@@ -32,7 +34,7 @@
     private boolean mPreviewEnabled;
     private boolean mHasValidGeometry;
 
-    public void setDrawingView(final DrawingPreviewPlacerView drawingView) {
+    public void setDrawingView(@Nonnull final DrawingPreviewPlacerView drawingView) {
         mDrawingView = drawingView;
         drawingView.addPreview(this);
     }
@@ -61,7 +63,7 @@
      * @param width the width of {@link MainKeyboardView}.
      * @param height the height of {@link MainKeyboardView}.
      */
-    public void setKeyboardViewGeometry(final int[] originCoords, final int width,
+    public void setKeyboardViewGeometry(@Nonnull final int[] originCoords, final int width,
             final int height) {
         mHasValidGeometry = (width > 0 && height > 0);
     }
@@ -72,11 +74,11 @@
      * Draws the preview
      * @param canvas The canvas where the preview is drawn.
      */
-    public abstract void drawPreview(final Canvas canvas);
+    public abstract void drawPreview(@Nonnull final Canvas canvas);
 
     /**
      * Set the position of the preview.
      * @param tracker The new location of the preview is based on the points in PointerTracker.
      */
-    public abstract void setPreviewPosition(final PointerTracker tracker);
+    public abstract void setPreviewPosition(@Nonnull final PointerTracker tracker);
 }
diff --git a/java/src/com/android/inputmethod/keyboard/internal/TimerHandler.java b/java/src/com/android/inputmethod/keyboard/internal/TimerHandler.java
index 814e8c4..ca5bb12 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/TimerHandler.java
+++ b/java/src/com/android/inputmethod/keyboard/internal/TimerHandler.java
@@ -32,9 +32,10 @@
 // TODO: Separate this class into KeyTimerHandler and BatchInputTimerHandler or so.
 public final class TimerHandler extends LeakGuardHandlerWrapper<Callbacks> implements TimerProxy {
     public interface Callbacks {
-        public void startWhileTypingFadeinAnimation();
-        public void startWhileTypingFadeoutAnimation();
-        public void onLongPress(PointerTracker tracker);
+        public static final int FADE_IN = 0;
+        public static final int FADE_OUT = 1;
+        public void startWhileTypingAnimation(final int fadeInOrOut);
+        public void onLongPress(@Nonnull PointerTracker tracker);
         public void dismissKeyPreviewWithoutDelay(@Nonnull Key key);
         public void dismissGestureFloatingPreviewTextWithoutDelay();
     }
@@ -66,7 +67,7 @@
         }
         switch (msg.what) {
         case MSG_TYPING_STATE_EXPIRED:
-            callbacks.startWhileTypingFadeinAnimation();
+            callbacks.startWhileTypingAnimation(Callbacks.FADE_IN);
             break;
         case MSG_REPEAT_KEY:
             final PointerTracker tracker1 = (PointerTracker) msg.obj;
@@ -163,7 +164,7 @@
         final int typedCode = typedKey.getCode();
         if (typedCode == Constants.CODE_SPACE || typedCode == Constants.CODE_ENTER) {
             if (isTyping) {
-                callbacks.startWhileTypingFadeinAnimation();
+                callbacks.startWhileTypingAnimation(Callbacks.FADE_IN);
             }
             return;
         }
@@ -173,7 +174,7 @@
         if (isTyping) {
             return;
         }
-        callbacks.startWhileTypingFadeoutAnimation();
+        callbacks.startWhileTypingAnimation(Callbacks.FADE_OUT);
     }
 
     @Override
diff --git a/java/src/com/android/inputmethod/latin/userdictionary/UserDictionarySettings.java b/java/src/com/android/inputmethod/latin/userdictionary/UserDictionarySettings.java
index 7274857..1d7e7d6 100644
--- a/java/src/com/android/inputmethod/latin/userdictionary/UserDictionarySettings.java
+++ b/java/src/com/android/inputmethod/latin/userdictionary/UserDictionarySettings.java
@@ -282,7 +282,6 @@
     }
 
     private static class MyAdapter extends SimpleCursorAdapter implements SectionIndexer {
-
         private AlphabetIndexer mIndexer;
 
         private ViewBinder mViewBinder = new ViewBinder() {