Support GridLayoutManager

library/src/main/java/com/timehop/stickyheadersrecyclerview/HeaderPositionCalculator.java

@@ -74,6 +74,13 @@ public boolean hasNewHeader(int position, boolean isReverseLayout) {
       return false;
     }
 
+    int numColumns = mAdapter.getNumColumns();
+    int columnOfItem = position % numColumns;
+    if (columnOfItem > 0) {
+      int firstItemOnRowPosition = position - columnOfItem;
+      return hasNewHeader(firstItemOnRowPosition, isReverseLayout);
+    }
+
     long headerId = mAdapter.getHeaderId(position);
 
     if (headerId < 0) {

library/src/main/java/com/timehop/stickyheadersrecyclerview/StickyRecyclerHeadersAdapter.java

@@ -36,4 +36,10 @@ public interface StickyRecyclerHeadersAdapter<VH extends RecyclerView.ViewHolder
    * @return the number of views in the adapter
    */
   int getItemCount();
+
+
+  /**
+   * @return the number of columns
+   */
+  int getNumColumns();
 }

library/src/main/java/com/timehop/stickyheadersrecyclerview/StickyRecyclerHeadersDecoration.java

@@ -100,7 +100,8 @@ public void onDrawOver(Canvas canvas, RecyclerView parent, RecyclerView.State st
     for (int i = 0; i < childCount; i++) {
       View itemView = parent.getChildAt(i);
       int position = parent.getChildAdapterPosition(itemView);
-      if (position == RecyclerView.NO_POSITION) {
+      if (position == RecyclerView.NO_POSITION ||
+              position % mAdapter.getNumColumns() > 0) {
           continue;
       }
 

sample/src/main/java/com/timehop/stickyheadersrecyclerview/sample/AnimalsAdapter.java

@@ -12,7 +12,7 @@
  */
 public abstract class AnimalsAdapter<VH extends RecyclerView.ViewHolder>
     extends RecyclerView.Adapter<VH> {
-  private ArrayList<String> items = new ArrayList<String>();
+  protected ArrayList<String> items = new ArrayList<String>();
 
   public AnimalsAdapter() {
     setHasStableIds(true);

sample/src/main/java/com/timehop/stickyheadersrecyclerview/sample/MainActivity.java

@@ -6,8 +6,10 @@
 import android.os.Handler;
 import android.os.Looper;
 import android.support.v7.app.AppCompatActivity;
+import android.support.v7.widget.GridLayoutManager;
 import android.support.v7.widget.LinearLayoutManager;
 import android.support.v7.widget.RecyclerView;
+import android.text.TextUtils;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
@@ -21,9 +23,12 @@
 import com.timehop.stickyheadersrecyclerview.StickyRecyclerHeadersTouchListener;
 
 import java.security.SecureRandom;
+import java.util.Collection;
 
 public class MainActivity extends AppCompatActivity {
 
+  private static final int NUM_COLUMNS = 3;
+
   @Override
   protected void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
@@ -35,7 +40,8 @@ protected void onCreate(Bundle savedInstanceState) {
 
     // Set adapter populated with example dummy data
     final AnimalsHeadersAdapter adapter = new AnimalsHeadersAdapter();
-    adapter.add("Animals below!");
+    adapter.setNumColumns(NUM_COLUMNS);
+//    adapter.add("Animals below!");
     adapter.addAll(getDummyDataSet());
     recyclerView.setAdapter(adapter);
 
@@ -58,7 +64,9 @@ public void run() {
 
     // Set layout manager
     int orientation = getLayoutManagerOrientation(getResources().getConfiguration().orientation);
-    final LinearLayoutManager layoutManager = new LinearLayoutManager(this, orientation, isReverseButton.isChecked());
+//    final LinearLayoutManager layoutManager = new LinearLayoutManager(this, orientation, isReverseButton.isChecked());
+
+    final GridLayoutManager layoutManager = new GridLayoutManager(this, NUM_COLUMNS);
     recyclerView.setLayoutManager(layoutManager);
 
     // Add the sticky headers decoration
@@ -118,6 +126,9 @@ private int getLayoutManagerOrientation(int activityOrientation) {
 
   private class AnimalsHeadersAdapter extends AnimalsAdapter<RecyclerView.ViewHolder>
       implements StickyRecyclerHeadersAdapter<RecyclerView.ViewHolder> {
+      private static final String EMPTY_NAME = " ";
+      private int numColumns = 1;
+
     @Override
     public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
       View view = LayoutInflater.from(parent.getContext())
@@ -134,11 +145,12 @@ public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
 
     @Override
     public long getHeaderId(int position) {
-      if (position == 0) {
-        return -1;
-      } else {
-        return getItem(position).charAt(0);
-      }
+        int numColumnOfItem = position % numColumns;
+        if (numColumnOfItem == 0) {
+            return getFirstChar(getItem(position));
+        } else {
+            return getHeaderId(position - numColumnOfItem);
+        }
     }
 
     @Override
@@ -163,5 +175,81 @@ private int getRandomColor() {
       });
     }
 
+    @Override
+    public int getNumColumns() {
+      return numColumns;
+    }
+
+    public void setNumColumns(int numColumns) {
+      this.numColumns = numColumns;
+    }
+
+      @Override
+      public void add(int index, String object) {
+          super.add(index, object);
+          reorderItems();
+      }
+
+      @Override
+      public void add(String object) {
+          super.add(object);
+          reorderItems();
+      }
+
+      @Override
+      public void addAll(Collection<? extends String> collection) {
+          super.addAll(collection);
+          reorderItems();
+      }
+
+      @Override
+      public void addAll(String... items) {
+          super.addAll(items);
+          reorderItems();
+      }
+
+      @Override
+      public void remove(String object) {
+          super.remove(object);
+          reorderItems();
+      }
+
+      private void reorderItems() {
+        long firstCharOnLastItem = -1;
+
+        for (int i = 0; i < items.size(); i++) {
+            String item = items.get(i);
+            if (getFirstChar(item) != firstCharOnLastItem) { // new header found for item
+                int numColumnOfItem = i % numColumns;
+                if (numColumnOfItem > 0 && !EMPTY_NAME.equals(item)) { // fill row with empty items
+                    int emptyVideos = numColumns - numColumnOfItem;
+                    for (int j = 0; j < emptyVideos; j++) {
+                        items.add(i, EMPTY_NAME);
+                        if (j != emptyVideos - 1) {
+                            i++;
+                        }
+                    }
+                    continue;
+                } else if (numColumnOfItem == 0 && EMPTY_NAME.equals(item)){
+                    // remove empty items to avoid empty rows when removing items
+                    while (items.get(i).equals(EMPTY_NAME)) {
+                        items.remove(i);
+                    }
+                    i--;
+                }
+                if (!EMPTY_NAME.equals(item)) {
+                    firstCharOnLastItem = getFirstChar(item);
+                }
+            }
+        }
+      }
+
+      private int getFirstChar(String name) {
+          if (TextUtils.isEmpty(name)) {
+              return 0;
+          } else {
+              return name.charAt(0);
+          }
+      }
   }
 }