Support different target-sizes for list items

library/src/androidTest/java/com/bumptech/glide/ListPreloaderTest.java

@@ -3,14 +3,26 @@ package com.bumptech.glide;
 import static com.google.common.truth.Truth.assertThat;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.atLeastOnce;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
 
+import com.bumptech.glide.request.target.SizeReadyCallback;
+import com.bumptech.glide.request.target.Target;
+
+import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
+import org.mockito.ArgumentCaptor;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+import org.mockito.verification.VerificationMode;
 import org.robolectric.RobolectricTestRunner;
 import org.robolectric.annotation.Config;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
@@ -21,21 +33,31 @@ import java.util.concurrent.atomic.AtomicInteger;
 @Config(manifest = Config.NONE, emulateSdk = 18)
 public class ListPreloaderTest {
 
+    @Mock
+    private BitmapRequestBuilder request;
+
+    @Before
+    public void setUp() throws Exception {
+        MockitoAnnotations.initMocks(this);
+    }
+
     @Test
     public void testGetItemsIsCalledIncreasing() {
         final AtomicBoolean called = new AtomicBoolean(false);
+        final AtomicInteger calledCount = new AtomicInteger();
+
         ListPreloaderAdapter preloaderAdapter = new ListPreloaderAdapter() {
             @Override
-            public List<Object> getPreloadItems(int start, int end) {
+            public List<Object> getPreloadItems(int position) {
                 called.set(true);
-                assertEquals(11, start);
-                assertEquals(21, end);
-                return super.getPreloadItems(start, end);
+                final int count = calledCount.getAndIncrement();
+                assertEquals(11 + count, position);
+                return super.getPreloadItems(position);
             }
         };
         ListPreloader<Object> preloader = new ListPreloader<Object>(preloaderAdapter, preloaderAdapter, 10);
         preloader.onScroll(null, 1, 10, 30);
-        assertTrue(called.get());
+        assertEquals(10, calledCount.get());
     }
 
     @Test
@@ -43,7 +65,7 @@ public class ListPreloaderTest {
         final int toPreload = 10;
         final List<Object> objects = new ArrayList<Object>();
         for (int i = 0; i < toPreload; i++) {
-            objects.add(new Object());
+            objects.add(new Integer(i));
         }
 
         ListPreloaderAdapter preloaderAdapter = new ListPreloaderAdapter() {
@@ -51,13 +73,13 @@ public class ListPreloaderTest {
             public int expectedPosition;
 
             @Override
-            public int[] getPreloadSize(Object item) {
+            public int[] getPreloadSize(Object item, int adapterPostion, int itemPosition) {
                 return new int[]{10, 10};
             }
 
             @Override
-            public List<Object> getPreloadItems(int start, int end) {
-                return objects;
+            public List<Object> getPreloadItems(int position) {
+                return objects.subList(position - 11, position + 1 - 11);
             }
 
             @Override
@@ -68,24 +90,25 @@ public class ListPreloaderTest {
             }
         };
         ListPreloader<Object> preloader = new ListPreloader<Object>(preloaderAdapter, preloaderAdapter,
-                                                                    toPreload);
-        preloader.onScroll(null, 1, 10, 30);
+                toPreload);
+        preloader.onScroll(null, 1, 10, 20);
     }
 
     @Test
     public void testGetItemsIsCalledDecreasing() {
         final AtomicBoolean called = new AtomicBoolean(false);
+        final AtomicInteger calledCount = new AtomicInteger();
         ListPreloaderAdapter preloaderAdapter = new ListPreloaderAdapter() {
             @Override
-            public List<Object> getPreloadItems(int start, int end) {
+            public List<Object> getPreloadItems(int position) {
                 // Ignore the preload caused from us starting at the end
-                if (start == 40) {
+                if (position >= 40) {
                     return Collections.emptyList();
                 }
+                final int count = calledCount.getAndIncrement();
                 called.set(true);
-                assertEquals(19, start);
-                assertEquals(29, end);
-                return super.getPreloadItems(start, end);
+                assertEquals(28 - count, position);
+                return super.getPreloadItems(position);
             }
         };
         ListPreloader<Object> preloader = new ListPreloader<Object>(preloaderAdapter, preloaderAdapter, 10);
@@ -106,16 +129,16 @@ public class ListPreloaderTest {
             int expectedPosition = toPreload - 1;
 
             @Override
-            public int[] getPreloadSize(Object item) {
+            public int[] getPreloadSize(Object item, int adapterPostion, int itemPosition) {
                 return new int[]{10, 10};
             }
 
             @Override
-            public List<Object> getPreloadItems(int start, int end) {
-                if (start == 40) {
-                    return Collections.emptyList();
+            public List<Object> getPreloadItems(int position) {
+                if (position == 40) {
+                    return null;
                 }
-                return objects;
+                return objects.subList(position, position + 1);
             }
 
             @Override
@@ -126,20 +149,21 @@ public class ListPreloaderTest {
             }
         };
         ListPreloader<Object> preloader = new ListPreloader<Object>(preloaderAdapter, preloaderAdapter, toPreload);
-        preloader.onScroll(null, 30, 10, 40);
-        preloader.onScroll(null, 29, 10, 40);
+        preloader.onScroll(null, 30, 10, 10);
+        preloader.onScroll(null, 29, 10, 10);
     }
 
     @Test
     public void testGetItemsIsNeverCalledWithEndGreaterThanTotalItems() {
         final AtomicBoolean called = new AtomicBoolean(false);
+        final AtomicInteger calledCount = new AtomicInteger();
         ListPreloaderAdapter preloaderAdapter = new ListPreloaderAdapter() {
             @Override
-            public List<Object> getPreloadItems(int start, int end) {
+            public List<Object> getPreloadItems(int position) {
                 called.set(true);
-                assertEquals(26, start);
-                assertEquals(30, end);
-                return super.getPreloadItems(start, end);
+                final int count = calledCount.getAndIncrement();
+                assertEquals(26 + count, position);
+                return super.getPreloadItems(position);
             }
         };
         ListPreloader<Object> preloader = new ListPreloader<Object>(preloaderAdapter, preloaderAdapter, 10);
@@ -150,16 +174,17 @@ public class ListPreloaderTest {
     @Test
     public void testGetItemsIsNeverCalledWithStartLessThanZero() {
         final AtomicBoolean called = new AtomicBoolean(false);
+        final AtomicInteger calledCount = new AtomicInteger();
         ListPreloaderAdapter preloaderAdapter = new ListPreloaderAdapter() {
             @Override
-            public List<Object> getPreloadItems(int start, int end) {
-                if (start == 17) {
+            public List<Object> getPreloadItems(int position) {
+                if (position >= 17) {
                     return Collections.emptyList();
                 }
                 called.set(true);
-                assertEquals(0, start);
-                assertEquals(6, end);
-                return super.getPreloadItems(start, end);
+                final int count = calledCount.getAndIncrement();
+                assertEquals(5 - count, position);
+                return super.getPreloadItems(position);
             }
         };
 
@@ -174,16 +199,10 @@ public class ListPreloaderTest {
         final AtomicInteger called = new AtomicInteger();
         ListPreloaderAdapter preloaderAdapter = new ListPreloaderAdapter() {
             @Override
-            public List<Object> getPreloadItems(int start, int end) {
+            public List<Object> getPreloadItems(int position) {
                 final int current = called.getAndIncrement();
-                if (current == 0) {
-                    assertEquals(11, start);
-                    assertEquals(21, end);
-                } else if (current == 1) {
-                    assertEquals(21, start);
-                    assertEquals(24, end);
-                }
-                return super.getPreloadItems(start, end);
+                assertEquals(11 + current, position);
+                return super.getPreloadItems(position);
             }
         };
 
@@ -191,7 +210,7 @@ public class ListPreloaderTest {
         preloader.onScroll(null, 1, 10, 30);
         preloader.onScroll(null, 4, 10, 30);
 
-        assertEquals(2, called.get());
+        assertEquals(13, called.get());
     }
 
     @Test
@@ -199,19 +218,13 @@ public class ListPreloaderTest {
         final AtomicInteger called = new AtomicInteger();
         ListPreloaderAdapter preloaderAdapter = new ListPreloaderAdapter() {
             @Override
-            public List<Object> getPreloadItems(int start, int end) {
-                if (start == 30) {
+            public List<Object> getPreloadItems(int position) {
+                if (position >= 20) {
                     return Collections.emptyList();
                 }
                 final int current = called.getAndIncrement();
-                if (current == 0) {
-                    assertEquals(10, start);
-                    assertEquals(20, end);
-                } else if (current == 1) {
-                    assertEquals(7, start);
-                    assertEquals(10, end);
-                }
-                return super.getPreloadItems(start, end);
+                assertEquals(19 - current, position);
+                return super.getPreloadItems(position);
             }
         };
 
@@ -219,7 +232,91 @@ public class ListPreloaderTest {
         preloader.onScroll(null, 21, 10, 30);
         preloader.onScroll(null, 20, 10, 30);
         preloader.onScroll(null, 17, 10, 30);
-        assertEquals(2, called.get());
+        assertEquals(13, called.get());
+    }
+
+    @Test
+    public void testMultipleItemsForPositionIncreasing() throws NoSuchFieldException {
+        final List<Object> objects = new ArrayList<Object>();
+        objects.add(new Object());
+        objects.add(new Object());
+        ListPreloaderAdapter preloaderAdapter = new ListPreloaderAdapter() {
+            public int expectedPosition = (1 + 10) * 2;
+
+            @Override
+            public List<Object> getPreloadItems(int position) {
+                return objects;
+            }
+
+            @Override
+            public int[] getPreloadSize(Object item, int adapterPostion, int itemPosition) {
+                assertEquals(expectedPosition / 2, adapterPostion);
+                assertEquals(expectedPosition % 2, itemPosition);
+                expectedPosition++;
+                return itemPosition == 0 ? new int[]{10, 11} : new int[]{20, 21};
+            }
+
+            @Override
+            public GenericRequestBuilder getPreloadRequestBuilder(Object item) {
+                return request;
+            }
+        };
+        ListPreloader<Object> preloader = new ListPreloader<Object>(preloaderAdapter, preloaderAdapter, 10);
+        Iterable<Integer> expected = Arrays.asList(10, 11, 20, 21, 10, 11, 20, 21);
+
+        preloader.onScroll(null, 1, 10, 1 + 10 + 2);
+
+        List<Integer> allValues = getTagetsSizes(request, times(4));
+        assertEquals(expected, allValues);
+    }
+
+    @Test
+    public void testMultipleItemsForPositionDecreasing() throws NoSuchFieldException {
+        final List<Object> objects = new ArrayList<Object>();
+        objects.add(new Object());
+        objects.add(new Object());
+        ListPreloaderAdapter preloaderAdapter = new ListPreloaderAdapter() {
+            int expectedPosition = objects.size() * 2 - 1;
+
+            @Override
+            public List<Object> getPreloadItems(int position) {
+                return objects;
+            }
+
+            @Override
+            public int[] getPreloadSize(Object item, int adapterPostion, int itemPosition) {
+                assertEquals(expectedPosition / 2, adapterPostion);
+                assertEquals(expectedPosition % 2, itemPosition);
+                expectedPosition--;
+                return itemPosition == 0 ? new int[]{10, 11} : new int[]{20, 21};
+            }
+
+            @Override
+            public GenericRequestBuilder getPreloadRequestBuilder(Object item) {
+                return request;
+            }
+        };
+        ListPreloader<Object> preloader = new ListPreloader<Object>(preloaderAdapter, preloaderAdapter, 10);
+        Iterable<Integer> expected = Arrays.asList(20, 21, 10, 11, 20, 21, 10, 11);
+
+        preloader.onScroll(null, 3, 2, 3 + 2);
+        preloader.onScroll(null, 2, 2, 3 + 2);
+
+        List<Integer> allValues = getTagetsSizes(request, times(4));
+        assertEquals(expected, allValues);
+    }
+
+    private List<Integer> getTagetsSizes(BitmapRequestBuilder requestBuilder, VerificationMode callVerificationMode) {
+        ArgumentCaptor<Integer> integerArgumentCaptor = ArgumentCaptor.forClass(Integer.class);
+        ArgumentCaptor<Target> targetArgumentCaptor = ArgumentCaptor.forClass(Target.class);
+        SizeReadyCallback cb = mock(SizeReadyCallback.class);
+        VerificationMode mode = atLeastOnce();
+        verify(requestBuilder, mode).into(targetArgumentCaptor.capture());
+        for (Target target : targetArgumentCaptor.getAllValues()) {
+            target.getSize(cb);
+        }
+        verify(cb, mode).onSizeReady(integerArgumentCaptor.capture(), integerArgumentCaptor.capture());
+        return integerArgumentCaptor.getAllValues();
     }
 
     @Test
@@ -230,8 +327,8 @@ public class ListPreloaderTest {
         final HashSet<Object> loadedObjects = new HashSet<Object>();
         ListPreloaderAdapter preloaderAdapter = new ListPreloaderAdapter() {
             @Override
-            public List<Object> getPreloadItems(int start, int end) {
-                return objects;
+            public List<Object> getPreloadItems(int position) {
+                return objects.subList(position - 11, position - 10);
             }
 
             @Override
@@ -241,7 +338,8 @@ public class ListPreloaderTest {
             }
         };
         ListPreloader<Object> preloader = new ListPreloader<Object>(preloaderAdapter, preloaderAdapter, 10);
-        preloader.onScroll(null, 1, 10, 30);
+
+        preloader.onScroll(null, 1, 10, 13);
         assertThat(loadedObjects).containsAllIn(objects);
     }
 
@@ -252,8 +350,8 @@ public class ListPreloaderTest {
         }
 
         @Override
-        public List<Object> getPreloadItems(int start, int end) {
-            ArrayList<Object> result = new ArrayList<Object>(end - start);
+        public List<Object> getPreloadItems(int position) {
+            ArrayList<Object> result = new ArrayList<Object>(1);
             Collections.fill(result, new Object());
             return result;
         }
@@ -264,7 +362,7 @@ public class ListPreloaderTest {
         }
 
         @Override
-        public int[] getPreloadSize(Object item) {
+        public int[] getPreloadSize(Object item, int adapterPostion, int itemPosition) {
             return new int[]{100, 100};
         }
     }

library/src/main/java/com/bumptech/glide/ListPreloader.java

@@ -14,7 +14,7 @@ import java.util.Queue;
  * Loads a few resources ahead in the direction of scrolling in any {@link AbsListView} so that images are in the memory
  * cache just before the corresponding view in created in the list. Gives the appearance of an infinitely large image
  * cache, depending on scrolling speed, cpu speed, and cache size.
- *
+ * <p/>
  * <p>
  * Must be set using {@link AbsListView#setOnScrollListener(android.widget.AbsListView.OnScrollListener)}, or have its
  * corresponding methods called from another {@link android.widget.AbsListView.OnScrollListener} to function.
@@ -25,7 +25,7 @@ import java.util.Queue;
 public class ListPreloader<T> implements AbsListView.OnScrollListener {
 
     private final int maxPreload;
-    private final PreloadTargetQueue preloadTargetQueue;
+    protected final PreloadTargetQueue preloadTargetQueue;
     private final PreloadModelProvider<T> preloadModelProvider;
     private final PreloadSizeProvider<T> preloadDimensionProvider;
 
@@ -38,6 +38,7 @@ public class ListPreloader<T> implements AbsListView.OnScrollListener {
 
     /**
      * An implementation of PreloadModelProvider should provide all the models that should be preloaded.
+     *
      * @param <U> The type of the model being preloaded.
      */
     public interface PreloadModelProvider<U> {
@@ -45,22 +46,19 @@ public class ListPreloader<T> implements AbsListView.OnScrollListener {
         /**
          * Returns a non null list of all models that need to be loaded for the list to display adapter items in
          * positions between {@code start} and {@code end}.
-         *
+         * <p/>
          * <p>
          * A list of any size can be returned so there can be multiple models per adapter position.
          * </p>
          *
-         * @param start The smallest adapter position. Will be {@code >= 0 && < adapter.getCount() &&
-         *              <= end}
-         * @param end   The largest adapter position. Will be {@code >= 0 && < adapter.getCount && >=
-         *              start}
+         * @param position The adapter position.
          */
-        List<U> getPreloadItems(int start, int end);
+        List<U> getPreloadItems(int position);
 
         /**
          * Returns a non null {@link com.bumptech.glide.GenericRequestBuilder} for a given item. Must exactly match
          * the request used to load the resource in the list.
-         *
+         * <p/>
          * <p>
          * The target and context will be provided by the preloader.
          * </p>
@@ -81,40 +79,60 @@ public class ListPreloader<T> implements AbsListView.OnScrollListener {
         /**
          * Returns the size of the view in the list where the resources will be displayed in pixels in the format
          * [x, y], or {@code null} if no size is currently available.
-         *
+         * <p/>
          * <p>
          * Note - The dimensions returned here must precisely match those of the view in the list.
          * </p>
          *
          * @param item A model
          */
-        int[] getPreloadSize(T item);
+        int[] getPreloadSize(T item, int adapterPosition, int perItemPosition);
     }
 
     /**
      * Constructor for {@link com.bumptech.glide.ListPreloader} that requires users to subclass and override
      * the {@link #getItems(int, int)} and {@link #getRequestBuilder(Object)} methods.
      *
+     * @param maxPreload Maximum number of items to preload.
      * @deprecated Use {@link #ListPreloader(com.bumptech.glide.ListPreloader.PreloadModelProvider,
      * com.bumptech.glide.ListPreloader.PreloadSizeProvider, int)} instead. This constructor will be removed in Glide
      * 4.0.
-     * @param maxPreload Maximum number of items to preload.
      */
     @Deprecated
     public ListPreloader(int maxPreload) {
-        this(null, null, maxPreload);
+        this.preloadModelProvider = new PreloadModelProvider<T>() {
+            @Override
+            public List<T> getPreloadItems(int position) {
+                return getItems(position, position + 1);
+            }
+
+            @Override
+            public GenericRequestBuilder getPreloadRequestBuilder(T item) {
+                return getRequestBuilder(item);
+            }
+        };
+        this.preloadDimensionProvider = new PreloadSizeProvider<T>() {
+
+            @Override
+            public int[] getPreloadSize(T item, int adapterPosition, int perItemPosition) {
+                return getDimensions(item);
+            }
+        };
+        this.maxPreload = maxPreload;
+        preloadTargetQueue = new PreloadTargetQueue(maxPreload + 1);
+
     }
 
     /**
      * Constructor for {@link com.bumptech.glide.ListPreloader} that accepts interfaces for providing the dimensions of
      * images to preload, the list of models to preload for a given position, and the request to use to load images.
      *
-     * @param preloadModelProvider Provides models to load and requests capable of loading them.
+     * @param preloadModelProvider     Provides models to load and requests capable of loading them.
      * @param preloadDimensionProvider Provides the dimensions of images to load.
-     * @param maxPreload Maximum number of items to preload.
+     * @param maxPreload               Maximum number of items to preload.
      */
     public ListPreloader(PreloadModelProvider<T> preloadModelProvider,
-                         PreloadSizeProvider<T> preloadDimensionProvider, int maxPreload) {
+            PreloadSizeProvider<T> preloadDimensionProvider, int maxPreload) {
         this.preloadModelProvider = preloadModelProvider;
         this.preloadDimensionProvider = preloadDimensionProvider;
         this.maxPreload = maxPreload;
@@ -128,7 +146,7 @@ public class ListPreloader<T> implements AbsListView.OnScrollListener {
 
     @Override
     public void onScroll(AbsListView absListView, int firstVisible, int visibleCount,
-                         int totalCount) {
+            int totalCount) {
         totalItemCount = totalCount;
         if (firstVisible > lastFirstVisible) {
             preload(firstVisible + visibleCount, true);
@@ -140,67 +158,59 @@ public class ListPreloader<T> implements AbsListView.OnScrollListener {
 
     /**
      * Returns the size of the view in the list where the resources will be displayed.
-     *
+     * <p/>
      * <p>
      * Note - The size returned here must precisely match those of the view in the list.
      * </p>
      *
-     * @deprecated Use {@link com.bumptech.glide.ListPreloader.PreloadSizeProvider} instead. This method will be removed
-     * in Glide 4.0.
      * @param item A model
      * @return The size of the view where the item will be displayed
+     * @deprecated Use {@link com.bumptech.glide.ListPreloader.PreloadSizeProvider} instead. This method will be removed
+     * in Glide 4.0.
      */
     @Deprecated
     protected int[] getDimensions(T item) {
-        if (preloadDimensionProvider == null) {
-            throw new IllegalStateException("You must either provide a PreloadDimensionProvider or override getSize9)");
-        }
-        return this.preloadDimensionProvider.getPreloadSize(item);
+        throw new IllegalStateException("You must either provide a PreloadDimensionProvider or override "
+                + "getDimensions()");
     }
 
     /**
      * Returns a non null list of all models that need to be loaded for the list to display adapter items
      * between {@code start} and {@code end}.
-     *
+     * <p/>
      * <p>
      * A list of any size can be returned so there can be multiple models per adapter position.
      * </p>
      *
-     * @deprecated Use {@link com.bumptech.glide.ListPreloader.PreloadModelProvider} instead. This method will be
-     * removed in Glide 4.0.
      * @param start The smallest adapter position. Will be {@code >= 0 && < adapter.getCount() &&
      *              <= end}
      * @param end   The largest adapter position. Will be {@code >= 0 && < adapter.getCount && >=
      *              start}
+     * @deprecated Use {@link com.bumptech.glide.ListPreloader.PreloadModelProvider} instead. This method will be
+     * removed in Glide 4.0.
      */
     @Deprecated
     protected List<T> getItems(int start, int end) {
-        if (preloadModelProvider == null) {
-            throw new IllegalStateException("You must either provide a PreloadModelProvider or override getItems()");
-        }
-        return this.preloadModelProvider.getPreloadItems(start, end);
+        throw new IllegalStateException("You must either provide a PreloadModelProvider or override getItems()");
     }
 
     /**
      * Returns a non null {@link com.bumptech.glide.GenericRequestBuilder} for a given item. Must exactly match the
      * request used to load the resource in the list.
-     *
+     * <p/>
      * <p>
      * The target and context will be provided by the preloader.
      * </p>
      *
+     * @param item The model to load.
      * @deprecated Use {@link com.bumptech.glide.ListPreloader.PreloadModelProvider} instead. This method will be
      * removed in Glide 4.0.
-     * @param item The model to load.
      */
     @SuppressWarnings("rawtypes")
     @Deprecated
     protected GenericRequestBuilder getRequestBuilder(T item) {
-        if (preloadModelProvider == null) {
-            throw new IllegalStateException("You must either provide a PreloadModelProvider, or override "
-                    + "getRequestBuilder()");
-        }
-        return this.preloadModelProvider.getPreloadRequestBuilder(item);
+        throw new IllegalStateException("You must either provide a PreloadModelProvider, or override "
+                + "getRequestBuilder()");
     }
 
     private void preload(int start, boolean increasing) {
@@ -223,18 +233,18 @@ public class ListPreloader<T> implements AbsListView.OnScrollListener {
         }
         end = Math.min(totalItemCount, end);
         start = Math.min(totalItemCount, Math.max(0, start));
-        List<T> items = getItems(start, end);
+//        List<T> items = getItems(start, end);
 
         if (from < to) {
             // Increasing
-            final int numItems = items.size();
-            for (int i = 0; i < numItems; i++) {
-                preloadItem(items, i);
+//            final int numItems = items.size();
+            for (int i = start; i < end; i++) {
+                preloadItem(this.preloadModelProvider.getPreloadItems(i), i, true);
             }
         } else {
             // Decreasing
-            for (int i = items.size() - 1; i >= 0; i--) {
-                preloadItem(items, i);
+            for (int i = end - 1; i >= start; i--) {
+                preloadItem(this.preloadModelProvider.getPreloadItems(i), i, false);
             }
         }
 
@@ -242,12 +252,25 @@ public class ListPreloader<T> implements AbsListView.OnScrollListener {
         lastEnd = end;
     }
 
+    private void preloadItem(List<T> items, int position, boolean isIncreasing) {
+        final int numItems = items.size();
+        if (isIncreasing) {
+            for (int i = 0; i < numItems; ++i) {
+                preloadItem(items.get(i), position, i);
+            }
+        } else {
+            for (int i = numItems - 1; i >= 0; --i) {
+                preloadItem(items.get(i), position, i);
+            }
+        }
+    }
+
     @SuppressWarnings("unchecked")
-    private void preloadItem(List<T> items, int position) {
-        final T item = items.get(position);
-        final int[] dimensions = getDimensions(item);
+    private void preloadItem(T item, int position, int i) {
+        final int[] dimensions = this.preloadDimensionProvider.getPreloadSize(item, position, i);
         if (dimensions != null) {
-            getRequestBuilder(item).into(preloadTargetQueue.next(dimensions[0], dimensions[1]));
+            GenericRequestBuilder preloadRequestBuilder = this.preloadModelProvider.getPreloadRequestBuilder(item);
+            preloadRequestBuilder.into(preloadTargetQueue.next(dimensions[0], dimensions[1]));
         }
     }
 
@@ -257,7 +280,7 @@ public class ListPreloader<T> implements AbsListView.OnScrollListener {
         }
     }
 
-    private static final class PreloadTargetQueue {
+    protected static final class PreloadTargetQueue {
         private final Queue<PreloadTarget> queue;
 
         public PreloadTargetQueue(int size) {
@@ -283,7 +306,7 @@ public class ListPreloader<T> implements AbsListView.OnScrollListener {
 
         @Override
         public void onResourceReady(Object resource,
-                                    GlideAnimation<? super Object> glideAnimation) {
+                GlideAnimation<? super Object> glideAnimation) {
             // Do nothing.
         }
 

library/src/main/java/com/bumptech/glide/util/FixedPreloadSizeProvider.java

@@ -24,7 +24,7 @@ public class FixedPreloadSizeProvider<T> implements ListPreloader.PreloadSizePro
     }
 
     @Override
-    public int[] getPreloadSize(T item) {
+    public int[] getPreloadSize(T item, int adapterPosition, int itemPosition) {
         return Arrays.copyOf(this.size, this.size.length);
     }
 }

library/src/main/java/com/bumptech/glide/util/ViewPreloadSizeProvider.java

@@ -38,7 +38,7 @@ public class ViewPreloadSizeProvider<T> implements ListPreloader.PreloadSizeProv
     }
 
     @Override
-    public int[] getPreloadSize(T item) {
+    public int[] getPreloadSize(T item, int adapterPosition, int itemPosition) {
         if (size == null) {
             return null;
         } else {

samples/flickr/src/main/java/com/bumptech/glide/samples/flickr/FlickrPhotoGrid.java

@@ -171,8 +171,8 @@ public class FlickrPhotoGrid extends Fragment implements PhotoViewer {
         }
 
         @Override
-        public List<Photo> getPreloadItems(int start, int end) {
-            return photos.subList(start, end);
+        public List<Photo> getPreloadItems(int position) {
+            return photos.subList(position, position + 1);
         }
 
         @Override

samples/flickr/src/main/java/com/bumptech/glide/samples/flickr/FlickrPhotoList.java

@@ -168,8 +168,8 @@ public class FlickrPhotoList extends Fragment implements PhotoViewer {
         }
 
         @Override
-        public List<Photo> getPreloadItems(int start, int end) {
-            return photos.subList(start, end);
+        public List<Photo> getPreloadItems(int position) {
+            return photos.subList(position, position + 1);
         }
 
         @Override

samples/giphy/src/main/java/com/bumptech/glide/samples/giphy/MainActivity.java

@@ -91,7 +91,7 @@ public class MainActivity extends Activity implements Api.Monitor {
         private Api.GifResult[] results = EMPTY_RESULTS;
 
         public GifAdapter(Activity activity, DrawableRequestBuilder<Api.GifResult> requestBuilder,
-                          ViewPreloadSizeProvider<Api.GifResult> preloadSizeProvider) {
+                ViewPreloadSizeProvider<Api.GifResult> preloadSizeProvider) {
             this.activity = activity;
             this.requestBuilder = requestBuilder;
             this.preloadSizeProvider = preloadSizeProvider;
@@ -155,11 +155,9 @@ public class MainActivity extends Activity implements Api.Monitor {
         }
 
         @Override
-        public List<Api.GifResult> getPreloadItems(int start, int end) {
-            List<Api.GifResult> items = new ArrayList<Api.GifResult>(end - start);
-            for (int i = start; i < end; i++) {
-                items.add(getItem(i));
-        }
+        public List<Api.GifResult> getPreloadItems(int position) {
+            List<Api.GifResult> items = new ArrayList<Api.GifResult>(1);
+            items.add(getItem(position));
             return items;
         }