Merge pull request timehop#90 from johngray1965/master

Added a check when searching for position of header, that the header …

Author: jacobtabak

README.md

@@ -83,6 +83,16 @@ The StickyHeaders aren't aware of your adapter so if you must notify them when y
     });
 ```
 
+If the Reccylerview's layout manager implements getExtraLayoutSpace (to preload more content then is visible for preformance resaons), you must implment ItemVisibilityAdapter and pass an instance as a second argment to StickyRecyclerHeadersDecoration's constuctor.
+```java
+    @Override
+    public boolean isPositionVisible(final int position) {
+        return layoutManager.findFirstVisibleItemPosition() <= position
+            && layoutManager.findLastVisibleItemPosition() >= position;
+    }
+```
+
+
 Item animators don't play nicely with RecyclerView decorations, so your mileage with that may vary.
 
 Compatibility

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

@@ -0,0 +1,28 @@
+package com.timehop.stickyheadersrecyclerview;
+
+/**
+ * ItemVisibilityAdapter provides a way for StickyRecyclerHeadersDecoration
+ * to know if a row is visible or not.  This comes into play if the
+ * recyclerview's layout manager  is set up to provide extra layout space (by
+ * overriding getExtraLayoutSpace). In this case rows that aren't visible (yet)
+ * will be bound and StickyRecyclerHeadersDecoration will need to know which
+ * are visible to correctly calculate the row to base the sticky header on
+ *
+ * To use it you must pass an instance of a class that implements this
+ * interface as a second argment StickyRecyclerHeadersDecoration's constructor.
+ *
+ */
+public interface ItemVisibilityAdapter {
+
+    /**
+     *
+     * Return true the specified adapter position is visible, false otherwise
+     *
+     * The implementation of this method will typically return true if
+     * the position is between the layout manager's findFirstVisibleItemPosition
+     * and findLastVisibleItemPosition (inclusive).
+     *
+     * @param position the adapter position
+     */
+    boolean isPositionVisible(final int position);
+}

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

@@ -17,6 +17,7 @@
 public class StickyRecyclerHeadersDecoration extends RecyclerView.ItemDecoration {
 
   private final StickyRecyclerHeadersAdapter mAdapter;
+  private final ItemVisibilityAdapter mVisibilityAdapter;
   private final SparseArray<Rect> mHeaderRects = new SparseArray<>();
   private final HeaderProvider mHeaderProvider;
   private final OrientationProvider mOrientationProvider;
@@ -32,31 +33,36 @@ public class StickyRecyclerHeadersDecoration extends RecyclerView.ItemDecoration
 
   // TODO: Consider passing in orientation to simplify orientation accounting within calculation
   public StickyRecyclerHeadersDecoration(StickyRecyclerHeadersAdapter adapter) {
-    this(adapter, new LinearLayoutOrientationProvider(), new DimensionCalculator());
+    this(adapter, new LinearLayoutOrientationProvider(), new DimensionCalculator(), null);
+  }
+
+  public StickyRecyclerHeadersDecoration(StickyRecyclerHeadersAdapter adapter, ItemVisibilityAdapter visibilityAdapter) {
+    this(adapter, new LinearLayoutOrientationProvider(), new DimensionCalculator(), visibilityAdapter);
   }
 
   private StickyRecyclerHeadersDecoration(StickyRecyclerHeadersAdapter adapter, OrientationProvider orientationProvider,
-      DimensionCalculator dimensionCalculator) {
+      DimensionCalculator dimensionCalculator, ItemVisibilityAdapter visibilityAdapter) {
     this(adapter, orientationProvider, dimensionCalculator, new HeaderRenderer(orientationProvider),
-        new HeaderViewCache(adapter, orientationProvider));
+        new HeaderViewCache(adapter, orientationProvider), visibilityAdapter);
   }
 
   private StickyRecyclerHeadersDecoration(StickyRecyclerHeadersAdapter adapter, OrientationProvider orientationProvider,
-      DimensionCalculator dimensionCalculator, HeaderRenderer headerRenderer, HeaderProvider headerProvider) {
+      DimensionCalculator dimensionCalculator, HeaderRenderer headerRenderer, HeaderProvider headerProvider, ItemVisibilityAdapter visibilityAdapter) {
     this(adapter, headerRenderer, orientationProvider, dimensionCalculator, headerProvider,
         new HeaderPositionCalculator(adapter, headerProvider, orientationProvider,
-            dimensionCalculator));
+            dimensionCalculator), visibilityAdapter);
   }
 
   private StickyRecyclerHeadersDecoration(StickyRecyclerHeadersAdapter adapter, HeaderRenderer headerRenderer,
       OrientationProvider orientationProvider, DimensionCalculator dimensionCalculator, HeaderProvider headerProvider,
-      HeaderPositionCalculator headerPositionCalculator) {
+      HeaderPositionCalculator headerPositionCalculator, ItemVisibilityAdapter visibilityAdapter) {
     mAdapter = adapter;
     mHeaderProvider = headerProvider;
     mOrientationProvider = orientationProvider;
     mRenderer = headerRenderer;
     mDimensionCalculator = dimensionCalculator;
     mHeaderPositionCalculator = headerPositionCalculator;
+    mVisibilityAdapter = visibilityAdapter;
   }
 
   @Override
@@ -130,7 +136,10 @@ public int findHeaderPositionUnder(int x, int y) {
     for (int i = 0; i < mHeaderRects.size(); i++) {
       Rect rect = mHeaderRects.get(mHeaderRects.keyAt(i));
       if (rect.contains(x, y)) {
-        return mHeaderRects.keyAt(i);
+        int position = mHeaderRects.keyAt(i);
+        if (mVisibilityAdapter == null || mVisibilityAdapter.isPositionVisible(position)) {
+          return position;
+        }
       }
     }
     return -1;