Added the ability to specify a view from the Header ViewHolder to make sticky instead of using the entire view

Author: brianwernick

demo/src/main/java/com/devbrackets/android/recyclerextdemo/ui/fragment/HeaderAsChildListFragment.java

@@ -119,5 +119,13 @@ public int getChildCount() {
         public long getHeaderId(int childPosition) {
             return items.get(childPosition).getOrder() / 10;
         }
+
+        /**
+         * Specifying this will make only the number field from the header be sticky
+         */
+        @Override
+        public int getCustomStickyHeaderViewId() {
+            return R.id.contacts_header_item_region_text_view;
+        }
     }
 }

demo/src/main/java/com/devbrackets/android/recyclerextdemo/ui/viewholder/ContactsHeaderViewHolder.java

@@ -34,8 +34,4 @@ public void setText(String text) {
     public void setRegionText(String text) {
         regionTextView.setText(text);
     }
-
-    public int getStickyViewId() {
-        return R.id.contacts_header_item_region_text_view;
-    }
 }

demo/src/main/res/layout/list_item_simple_text.xml

@@ -21,8 +21,8 @@
     <TextView
         android:id="@+id/simple_text_text_view"
         android:layout_width="match_parent"
-        android:layout_height="wrap_content"
-        android:layout_gravity="center_vertical"
+        android:layout_height="match_parent"
+        android:gravity="center_vertical"
         android:paddingLeft="16dp"
         tools:ignore="RtlHardcoded,RtlSymmetry"
         tools:text="Lorem Ipsum Dolor Sit Amet"/>

library/src/main/java/com/devbrackets/android/recyclerext/adapter/RecyclerHeaderAdapter.java

@@ -180,6 +180,11 @@ public void showHeaderAsChild(boolean enabled) {
         core.showHeaderAsChild(enabled);
     }
 
+    @Override
+    public int getCustomStickyHeaderViewId() {
+        return 0;
+    }
+
     /**
      * Initializes the non-super components for the Adapter
      */

library/src/main/java/com/devbrackets/android/recyclerext/adapter/RecyclerHeaderCursorAdapter.java

@@ -209,6 +209,11 @@ public void showHeaderAsChild(boolean enabled) {
         core.showHeaderAsChild(enabled);
     }
 
+    @Override
+    public int getCustomStickyHeaderViewId() {
+        return 0;
+    }
+
     /**
      * Initializes the non-super components for the Adapter
      */

library/src/main/java/com/devbrackets/android/recyclerext/adapter/header/HeaderApi.java

@@ -118,4 +118,19 @@ public interface HeaderApi<H extends RecyclerView.ViewHolder, C extends Recycler
      * @param enabled True if the header should be treated as a child
      */
     void showHeaderAsChild(boolean enabled);
+
+    /**
+     * Retrieves the resource id for the view in the header
+     * view holder to make sticky.  By default this returns
+     * the invalid resource id (0) and will use the entire
+     * header view.  Only use this if only a specific view
+     * should remain sticky.
+     * <p>
+     * <b>NOTE:</b> This will only be used when a
+     * {@link com.devbrackets.android.recyclerext.decoration.StickyHeaderDecoration}
+     * has been specified
+     *
+     * @return The resource id for the view that will be sticky
+     */
+    int getCustomStickyHeaderViewId();
 }

library/src/main/java/com/devbrackets/android/recyclerext/decoration/StickyHeaderDecoration.java

@@ -50,7 +50,7 @@ public enum LayoutOrientation {
     private AdapterDataObserver dataObserver;
     private StickyViewScrollListener scrollListener;
 
-    private int stickyHeaderStart = 0;
+    private int stickyHeaderLeft, stickyHeaderTop;
     private long currentStickyId = Long.MIN_VALUE;
     private LayoutOrientation orientation = LayoutOrientation.VERTICAL;
 
@@ -84,9 +84,7 @@ public StickyHeaderDecoration(RecyclerView parent) {
     @Override
     public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
         if (stickyHeader != null) {
-            int x = orientation == LayoutOrientation.HORIZONTAL ? stickyHeaderStart : 0;
-            int y = orientation == LayoutOrientation.HORIZONTAL ? 0 : stickyHeaderStart;
-            c.drawBitmap(stickyHeader, x, y, null);
+            c.drawBitmap(stickyHeader, stickyHeaderLeft, stickyHeaderTop, null);
         }
     }
 
@@ -114,7 +112,6 @@ public void clearStickyHeader() {
         }
 
         stickyHeader = null;
-        stickyHeaderStart = 0;
         currentStickyId = RecyclerView.NO_ID;
     }
 
@@ -144,6 +141,10 @@ public LayoutOrientation getOrientation() {
      * @return The bitmap representing the drag view
      */
     private Bitmap createStickyViewBitmap(View view) {
+        //Makes sure the location opposite the scroll orientation is persisted
+         stickyHeaderLeft = orientation == LayoutOrientation.HORIZONTAL ? 0 : view.getLeft();
+         stickyHeaderTop = orientation == LayoutOrientation.VERTICAL ? 0 : view.getTop();
+
         Rect stickyViewBounds = new Rect(0, 0, view.getRight() - view.getLeft(), view.getBottom() - view.getTop());
 
         Bitmap bitmap = Bitmap.createBitmap(stickyViewBounds.width(), stickyViewBounds.height(), Bitmap.Config.ARGB_8888);
@@ -235,8 +236,19 @@ private void updateHeader(long headerId, int headerPosition) {
                 return;
             }
 
-            stickyHeaderStart = 0;
             currentStickyId = headerId;
+
+            //Creates the actual sticky header (or view)
+            int stickyViewId = getCustomStickyViewId();
+            if (stickyViewId != 0) {
+                View stickyView = holder.itemView.findViewById(stickyViewId);
+                if (stickyView != null) {
+                    stickyHeader = createStickyViewBitmap(stickyView);
+                    return;
+                }
+            }
+
+            //If the user hasn't specified a sticky view id or it was null, use the entire view holder
             stickyHeader = createStickyViewBitmap(holder.itemView);
         }
 
@@ -319,6 +331,14 @@ private int getHeaderViewType(int headerPosition) {
             return rawType | HeaderApi.HEADER_VIEW_TYPE_MASK;
         }
 
+        private int getCustomStickyViewId() {
+            if (adapter instanceof RecyclerHeaderAdapter) {
+                return ((RecyclerHeaderAdapter)adapter).getCustomStickyHeaderViewId();
+            }
+
+            return ((RecyclerHeaderCursorAdapter) adapter).getCustomStickyHeaderViewId();
+        }
+
         /**
          * Retrieves the ViewHolder associated with the header at <code>headerPosition</code>.
          * If the ViewHolder returned from <code>parent</code> is null then a temporary ViewHolder