Minor changes

 - Changed Add/Remove OnSelectionChangedListener to setOnSelectionChangedListener
 - Fixed minor bug where duplicate updates were showing up in the listener
 - Update README

README.md

@@ -137,11 +137,10 @@ The item selected, in the middle underlying the query `EditText`, can be found t
 int position = ReelSearchView.getSelection()
 ```
 
-#### Add/Remove OnSelectionChangedListener(s)
+#### Set OnSelectionChangedListener
 
 ```java
-ReelSearchView.addOnSelectionChangedListener(listener);
-ReelSearchView.removeOnSelectionChangedListener(listener);
+ReelSearchView.setOnSelectionChangedListener(listener);
 ```
 
 #### Child transformer

app/src/main/java/com/suhel/reelsearch/SuggestionsActivity.java

@@ -59,7 +59,7 @@ protected void onCreate(@Nullable Bundle savedInstanceState) {
         mBinding.txtQuery.setFilters(new InputFilter[]{
                 (source, start, end, dest, dstart, dend) -> source.toString().toLowerCase().trim()
         });
-        mBinding.reelSearch.addOnSelectionChangedListener((prevSelection, newSelection) -> {
+        mBinding.reelSearch.setOnSelectionChangedListener((prevSelection, newSelection) -> {
             Log.e("Selection", "Changed to " + newSelection + " from " + prevSelection);
         });
     }

library/src/main/java/com/suhel/library/CenteredLayoutManager.java

@@ -32,9 +32,6 @@
 import android.view.View;
 import android.view.ViewGroup;
 
-import java.util.HashSet;
-import java.util.Set;
-
 /**
  * A custom {@link android.support.v7.widget.RecyclerView.LayoutManager} which
  * applies top and bottom offsets to achieve a reel effect
@@ -45,7 +42,7 @@ public class CenteredLayoutManager extends RecyclerView.LayoutManager {
      * Stores the references of {@link OnSelectionChangedListener} delegates
      * to inform about change in selection
      */
-    private final Set<OnSelectionChangedListener> mOnSelectionChangedListeners;
+    private OnSelectionChangedListener mOnSelectionChangedListener;
 
     /**
      * Stores the absolute scroll value
@@ -58,6 +55,11 @@ public class CenteredLayoutManager extends RecyclerView.LayoutManager {
      */
     private int mMaxScrollY;
 
+    /**
+     * Stores the number of total items in the adapter
+     */
+    private int mChildCount;
+
     /**
      * Stores the height of each child assuming
      * the children are homogeneous
@@ -95,7 +97,6 @@ public class CenteredLayoutManager extends RecyclerView.LayoutManager {
      * Constructor to initialize required members
      */
     public CenteredLayoutManager() {
-        mOnSelectionChangedListeners = new HashSet<>();
         mPreviousSelection = -1;
     }
 
@@ -155,9 +156,11 @@ public RecyclerView.LayoutParams generateDefaultLayoutParams() {
     public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
         detachAllViews(recycler);
 
-        if (state.getItemCount() != 0) {
+        mChildCount = state.getItemCount();
+
+        if (mChildCount != 0) {
             calculateDimensions(recycler, state);
-            render(recycler, state);
+            render(recycler);
             recycle(recycler);
         }
     }
@@ -169,15 +172,17 @@ public boolean canScrollVertically() {
 
     @Override
     public int scrollVerticallyBy(int dy, RecyclerView.Recycler recycler, RecyclerView.State state) {
-        if(state.getItemCount() < 2) {
+        mChildCount = state.getItemCount();
+
+        if (mChildCount < 2) {
             return 0;
         }
 
         final int lastScrollY = mScrollY;
         mScrollY = Math.min(Math.max(mScrollY + dy, 0), mMaxScrollY);
 
         detachAllViews(recycler);
-        render(recycler, state);
+        render(recycler);
         recycle(recycler);
 
         return mScrollY - lastScrollY;
@@ -195,8 +200,9 @@ public void onScrollStateChanged(int state) {
 
                 if (newSelection != mPreviousSelection) {
                     // Inform all listeners about the event
-                    for (final OnSelectionChangedListener listener : mOnSelectionChangedListeners) {
-                        listener.onSelectionChanged(mPreviousSelection, newSelection);
+
+                    if (mOnSelectionChangedListener != null) {
+                        mOnSelectionChangedListener.onSelectionChanged(mPreviousSelection, newSelection);
                     }
 
                     // For the next time
@@ -210,22 +216,12 @@ public void onScrollStateChanged(int state) {
     }
 
     /**
-     * Adds a {@link OnSelectionChangedListener} to the set of listeners.
-     * This method ensures duplicates are not added
+     * Sets the {@link OnSelectionChangedListener}
      *
-     * @param listener The {@link OnSelectionChangedListener} to be added
+     * @param listener The {@link OnSelectionChangedListener} to be set
      */
-    public void addOnSelectionChangedListener(@NonNull OnSelectionChangedListener listener) {
-        mOnSelectionChangedListeners.add(listener);
-    }
-
-    /**
-     * Removes a {@link OnSelectionChangedListener} from the set of listeners
-     *
-     * @param listener The {@link OnSelectionChangedListener} to be removed
-     */
-    public void removeOnSelectionChangedListener(@NonNull OnSelectionChangedListener listener) {
-        mOnSelectionChangedListeners.remove(listener);
+    public void setOnSelectionChangedListener(@Nullable OnSelectionChangedListener listener) {
+        mOnSelectionChangedListener = listener;
     }
 
     /**
@@ -243,24 +239,22 @@ public int getSelection() {
      *
      * @param recycler The {@link android.support.v7.widget.RecyclerView.Recycler}
      *                 passed for getting inflated and data bound children
-     * @param state    The {@link android.support.v7.widget.RecyclerView.State}
-     *                 passed for getting item count
      */
-    private void render(RecyclerView.Recycler recycler, RecyclerView.State state) {
-        if (state.getItemCount() == 0) {
+    private void render(RecyclerView.Recycler recycler) {
+        if (mChildCount == 0) {
             return;
         }
 
         final int firstIndex = (mScrollY >= mTopOffset) ?
-                Math.min((mScrollY - mTopOffset) / mChildHeight, state.getItemCount() - 1) :
+                Math.min((mScrollY - mTopOffset) / mChildHeight, mChildCount - 1) :
                 0;
 
         final int firstTop = (mScrollY >= mTopOffset) ?
                 -((mScrollY - mTopOffset) % mChildHeight) :
                 mTopOffset - mScrollY;
 
         for (int i = firstIndex, top = firstTop, bottom;
-             i < state.getItemCount() && top < getParentBottom();
+             i < mChildCount && top < getParentBottom();
              i++, top = bottom) {
 
             View v = recycler.getViewForPosition(i);
@@ -380,7 +374,8 @@ public interface OnSelectionChangedListener {
          * Called with the new selection value once the view
          * has settled at a particular position from scroll
          *
-         * @param selection The new selection
+         * @param previousSelection The previous selection
+         * @param newSelection      The new selection
          */
         void onSelectionChanged(int previousSelection, int newSelection);
 

library/src/main/java/com/suhel/library/ReelSearchView.java

@@ -2,6 +2,7 @@
 
 import android.content.Context;
 import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v7.widget.LinearSnapHelper;
 import android.support.v7.widget.RecyclerView;
 import android.util.AttributeSet;
@@ -131,24 +132,13 @@ public CenteredLayoutManager getLayoutManager() {
     }
 
     /**
-     * Adds a {@link CenteredLayoutManager.OnSelectionChangedListener} to the set of listeners
+     * Sets the {@link CenteredLayoutManager.OnSelectionChangedListener}
      * of the associated {@link CenteredLayoutManager}.
-     * This method ensures duplicates are not added
      *
-     * @param listener The {@link CenteredLayoutManager.OnSelectionChangedListener} to be added
+     * @param listener The {@link CenteredLayoutManager.OnSelectionChangedListener} to be set
      */
-    public void addOnSelectionChangedListener(@NonNull CenteredLayoutManager.OnSelectionChangedListener listener) {
-        getLayoutManager().addOnSelectionChangedListener(listener);
-    }
-
-    /**
-     * Removes a {@link CenteredLayoutManager.OnSelectionChangedListener} from the set of listeners
-     * of the associated {@link CenteredLayoutManager}
-     *
-     * @param listener The {@link CenteredLayoutManager.OnSelectionChangedListener} to be removed
-     */
-    public void removeOnSelectionChangedListener(@NonNull CenteredLayoutManager.OnSelectionChangedListener listener) {
-        getLayoutManager().removeOnSelectionChangedListener(listener);
+    public void setOnSelectionChangedListener(@Nullable CenteredLayoutManager.OnSelectionChangedListener listener) {
+        getLayoutManager().setOnSelectionChangedListener(listener);
     }
 
     /**