Update documentation for FastScroller and SectionIndexer

BUG: 3341285
Change-Id: I0607031576eaaecaebe848437cfbacd0d1a4b161

core/java/android/widget/AbsListView.java

@@ -1211,13 +1211,19 @@ public abstract class AbsListView extends AdapterView<ListAdapter> implements Te
     }
 
     /**
-     * Enables fast scrolling by letting the user quickly scroll through lists by
-     * dragging the fast scroll thumb. The adapter attached to the list may want
-     * to implement {@link SectionIndexer} if it wishes to display alphabet preview and
-     * jump between sections of the list.
+     * Specifies whether fast scrolling is enabled or disabled.
+     * <p>
+     * When fast scrolling is enabled, the user can quickly scroll through lists
+     * by dragging the fast scroll thumb.
+     * <p>
+     * If the adapter backing this list implements {@link SectionIndexer}, the
+     * fast scroller will display section header previews as the user scrolls.
+     * Additionally, the user will be able to quickly jump between sections by
+     * tapping along the length of the scroll bar.
+     *
      * @see SectionIndexer
      * @see #isFastScrollEnabled()
-     * @param enabled whether or not to enable fast scrolling
+     * @param enabled true to enable fast scrolling, false otherwise
      */
     public void setFastScrollEnabled(final boolean enabled) {
         if (mFastScrollEnabled != enabled) {
@@ -1252,13 +1258,16 @@ public abstract class AbsListView extends AdapterView<ListAdapter> implements Te
     }
 
     /**
-     * Set whether or not the fast scroller should always be shown in place of the
-     * standard scrollbars. Fast scrollers shown in this way will not fade out and will
-     * be a permanent fixture within the list. Best combined with an inset scroll bar style
-     * that will ensure enough padding. This will enable fast scrolling if it is not
+     * Set whether or not the fast scroller should always be shown in place of
+     * the standard scroll bars. This will enable fast scrolling if it is not
      * already enabled.
+     * <p>
+     * Fast scrollers shown in this way will not fade out and will be a
+     * permanent fixture within the list. This is best combined with an inset
+     * scroll bar style to ensure the scroll bar does not overlap content.
      *
-     * @param alwaysShow true if the fast scroller should always be displayed.
+     * @param alwaysShow true if the fast scroller should always be displayed,
+     *            false otherwise
      * @see #setScrollBarStyle(int)
      * @see #setFastScrollEnabled(boolean)
      */
@@ -1297,10 +1306,9 @@ public abstract class AbsListView extends AdapterView<ListAdapter> implements Te
     }
 
     /**
-     * Returns true if the fast scroller is set to always show on this view rather than
-     * fade out when not in use.
+     * Returns true if the fast scroller is set to always show on this view.
      *
-     * @return true if the fast scroller will always show.
+     * @return true if the fast scroller will always show
      * @see #setFastScrollAlwaysVisible(boolean)
      */
     public boolean isFastScrollAlwaysVisible() {
@@ -1316,7 +1324,8 @@ public abstract class AbsListView extends AdapterView<ListAdapter> implements Te
     }
 
     /**
-     * Returns the current state of the fast scroll feature.
+     * Returns true if the fast scroller is enabled.
+     *
      * @see #setFastScrollEnabled(boolean)
      * @return true if fast scroll is enabled, false otherwise
      */

core/java/android/widget/SectionIndexer.java

@@ -17,38 +17,62 @@
 package android.widget;
 
 /**
- * Interface that should be implemented on Adapters to enable fast scrolling 
- * in an {@link AbsListView} between sections of the list. A section is a group of list items
- * to jump to that have something in common. For example, they may begin with the
- * same letter or they may be songs from the same artist. ExpandableListAdapters that
- * consider groups and sections as synonymous should account for collapsed groups and return
- * an appropriate section/position.
+ * Interface that may implemented on {@link Adapter}s to enable fast scrolling
+ * between sections of an {@link AbsListView}.
+ * <p>
+ * A section is a group of list items that have something in common. For
+ * example, they may begin with the same letter or they may be songs from the
+ * same artist.
+ * <p>
+ * {@link ExpandableListAdapter}s that consider groups and sections as
+ * synonymous should account for collapsed groups and return an appropriate
+ * section/position.
+ *
+ * @see AbsListView#setFastScrollEnabled(boolean)
  */
 public interface SectionIndexer {
     /**
-     * This provides the list view with an array of section objects. In the simplest
-     * case these are Strings, each containing one letter of the alphabet.
-     * They could be more complex objects that indicate the grouping for the adapter's
-     * consumption. The list view will call toString() on the objects to get the
-     * preview letter to display while scrolling.
-     * @return the array of objects that indicate the different sections of the list.
+     * Returns an array of objects representing sections of the list. The
+     * returned array and its contents should be non-null.
+     * <p>
+     * The list view will call toString() on the objects to get the preview text
+     * to display while scrolling. For example, an adapter may return an array
+     * of Strings representing letters of the alphabet. Or, it may return an
+     * array of objects whose toString() methods return their section titles.
+     *
+     * @return the array of section objects
      */
     Object[] getSections();
-    
+
     /**
-     * Provides the starting index in the list for a given section.
-     * @param section the index of the section to jump to.
-     * @return the starting position of that section. If the section is out of bounds, the
-     * position must be clipped to fall within the size of the list.
+     * Given the index of a section within the array of section objects, returns
+     * the starting position of that section within the adapter.
+     * <p>
+     * If the section's starting position is outside of the adapter bounds, the
+     * position must be clipped to fall within the size of the adapter.
+     *
+     * @param sectionIndex the index of the section within the array of section
+     *            objects
+     * @return the starting position of that section within the adapter,
+     *         constrained to fall within the adapter bounds
      */
-    int getPositionForSection(int section);
-    
+    int getPositionForSection(int sectionIndex);
+
     /**
-     * This is a reverse mapping to fetch the section index for a given position
-     * in the list.
-     * @param position the position for which to return the section
-     * @return the section index. If the position is out of bounds, the section index
+     * Given a position within the adapter, returns the index of the
+     * corresponding section within the array of section objects.
+     * <p>
+     * If the section index is outside of the section array bounds, the index
      * must be clipped to fall within the size of the section array.
+     * <p>
+     * For example, consider an indexer where the section at array index 0
+     * starts at adapter position 100. Calling this method with position 10,
+     * which is before the first section, must return index 0.
+     *
+     * @param position the position within the adapter for which to return the
+     *            corresponding section index
+     * @return the index of the corresponding section within the array of
+     *         section objects, constrained to fall within the array bounds
      */
-    int getSectionForPosition(int position);    
+    int getSectionForPosition(int position);
 }