Support custom RecyclerView preload positions

integration/recyclerview/build.gradle.kts

@@ -21,6 +21,12 @@ dependencies {
     implementation(project(":library"))
     compileOnly(libs.androidx.recyclerview)
     compileOnly(libs.androidx.fragment)
+
+    testImplementation(libs.androidx.recyclerview)
+    testImplementation(libs.androidx.test.core)
+    testImplementation(libs.junit)
+    testImplementation(libs.robolectric)
+    testImplementation(libs.truth)
 }
 
-apply(from = "${rootProject.projectDir}/scripts/upload.gradle.kts")
+apply(from = "${rootProject.projectDir}/scripts/upload.gradle.kts")

integration/recyclerview/src/main/java/com/bumptech/glide/integration/recyclerview/RecyclerToListViewScrollListener.java

@@ -17,12 +17,20 @@
 public final class RecyclerToListViewScrollListener extends RecyclerView.OnScrollListener {
   public static final int UNKNOWN_SCROLL_STATE = Integer.MIN_VALUE;
   private final AbsListView.OnScrollListener scrollListener;
+  private final RecyclerViewPositionProvider positionProvider;
   private int lastFirstVisible = -1;
   private int lastVisibleCount = -1;
   private int lastItemCount = -1;
 
   public RecyclerToListViewScrollListener(@NonNull AbsListView.OnScrollListener scrollListener) {
+    this(scrollListener, new LinearLayoutManagerPositionProvider());
+  }
+
+  public RecyclerToListViewScrollListener(
+      @NonNull AbsListView.OnScrollListener scrollListener,
+      @NonNull RecyclerViewPositionProvider positionProvider) {
     this.scrollListener = scrollListener;
+    this.positionProvider = positionProvider;
   }
 
   @Override
@@ -47,10 +55,8 @@ public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
 
   @Override
   public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
-    LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();
-
-    int firstVisible = layoutManager.findFirstVisibleItemPosition();
-    int visibleCount = Math.abs(firstVisible - layoutManager.findLastVisibleItemPosition());
+    int firstVisible = positionProvider.getFirstVisiblePosition(recyclerView);
+    int visibleCount = positionProvider.getVisibleItemCount(recyclerView);
     int itemCount = recyclerView.getAdapter().getItemCount();
 
     if (firstVisible != lastFirstVisible
@@ -62,4 +68,27 @@ public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
       lastItemCount = itemCount;
     }
   }
+
+  private static final class LinearLayoutManagerPositionProvider
+      implements RecyclerViewPositionProvider {
+    @Override
+    public int getFirstVisiblePosition(@NonNull RecyclerView recyclerView) {
+      return getLayoutManager(recyclerView).findFirstVisibleItemPosition();
+    }
+
+    @Override
+    public int getVisibleItemCount(@NonNull RecyclerView recyclerView) {
+      LinearLayoutManager layoutManager = getLayoutManager(recyclerView);
+      int firstVisible = layoutManager.findFirstVisibleItemPosition();
+      int lastVisible = layoutManager.findLastVisibleItemPosition();
+      if (firstVisible == RecyclerView.NO_POSITION || lastVisible == RecyclerView.NO_POSITION) {
+        return 0;
+      }
+      return Math.abs(lastVisible - firstVisible) + 1;
+    }
+
+    private static LinearLayoutManager getLayoutManager(RecyclerView recyclerView) {
+      return (LinearLayoutManager) recyclerView.getLayoutManager();
+    }
+  }
 }

integration/recyclerview/src/main/java/com/bumptech/glide/integration/recyclerview/RecyclerViewPositionProvider.java

@@ -0,0 +1,17 @@
+package com.bumptech.glide.integration.recyclerview;
+
+import androidx.annotation.NonNull;
+import androidx.recyclerview.widget.RecyclerView;
+
+/**
+ * Provides visible adapter position metadata from a {@link RecyclerView}.
+ *
+ * <p>Implement this interface to use {@link RecyclerViewPreloader} with custom {@link
+ * RecyclerView.LayoutManager} implementations that do not extend {@link
+ * androidx.recyclerview.widget.LinearLayoutManager}.
+ */
+public interface RecyclerViewPositionProvider {
+  int getFirstVisiblePosition(@NonNull RecyclerView recyclerView);
+
+  int getVisibleItemCount(@NonNull RecyclerView recyclerView);
+}

integration/recyclerview/src/main/java/com/bumptech/glide/integration/recyclerview/RecyclerViewPreloader.java

@@ -22,8 +22,11 @@
  * methods called from another {@link androidx.recyclerview.widget.RecyclerView.OnScrollListener} to
  * function.
  *
- * <p>This class only works with {@link androidx.recyclerview.widget.LinearLayoutManager} and
- * subclasses of {@link androidx.recyclerview.widget.LinearLayoutManager}.
+ * <p>By default this class only works with {@link
+ * androidx.recyclerview.widget.LinearLayoutManager} and subclasses of {@link
+ * androidx.recyclerview.widget.LinearLayoutManager}. To support another {@link
+ * RecyclerView.LayoutManager}, use the constructor that accepts a {@link
+ * RecyclerViewPositionProvider}.
  *
  * @param <T> The type of the model being displayed in the {@link RecyclerView}.
  */
@@ -94,6 +97,29 @@ public RecyclerViewPreloader(
     recyclerScrollListener = new RecyclerToListViewScrollListener(listPreloader);
   }
 
+  /**
+   * Constructor that accepts a {@link RecyclerViewPositionProvider} for custom {@link
+   * RecyclerView.LayoutManager} implementations.
+   *
+   * @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 positionProvider Provides visible adapter position metadata.
+   */
+  public RecyclerViewPreloader(
+      @NonNull RequestManager requestManager,
+      @NonNull PreloadModelProvider<T> preloadModelProvider,
+      @NonNull PreloadSizeProvider<T> preloadDimensionProvider,
+      int maxPreload,
+      @NonNull RecyclerViewPositionProvider positionProvider) {
+
+    ListPreloader<T> listPreloader =
+        new ListPreloader<>(
+            requestManager, preloadModelProvider, preloadDimensionProvider, maxPreload);
+    recyclerScrollListener =
+        new RecyclerToListViewScrollListener(listPreloader, positionProvider);
+  }
+
   @Override
   public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
     recyclerScrollListener.onScrolled(recyclerView, dx, dy);

integration/recyclerview/src/test/java/com/bumptech/glide/integration/recyclerview/RecyclerToListViewScrollListenerTest.java

@@ -0,0 +1,139 @@
+package com.bumptech.glide.integration.recyclerview;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import android.content.Context;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.AbsListView;
+import androidx.annotation.NonNull;
+import androidx.recyclerview.widget.LinearLayoutManager;
+import androidx.recyclerview.widget.RecyclerView;
+import androidx.test.core.app.ApplicationProvider;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+
+@RunWith(RobolectricTestRunner.class)
+public final class RecyclerToListViewScrollListenerTest {
+  @Test
+  public void onScrolled_withCustomPositionProvider_forwardsScrollValues() {
+    RecyclerView recyclerView = newRecyclerViewWithAdapter(20);
+    RecordingOnScrollListener scrollListener = new RecordingOnScrollListener();
+    RecyclerToListViewScrollListener listener =
+        new RecyclerToListViewScrollListener(
+            scrollListener, new FixedPositionProvider(7, 3));
+
+    listener.onScrolled(recyclerView, /* dx= */ 0, /* dy= */ 5);
+
+    assertThat(scrollListener.callCount).isEqualTo(1);
+    assertThat(scrollListener.firstVisible).isEqualTo(7);
+    assertThat(scrollListener.visibleCount).isEqualTo(3);
+    assertThat(scrollListener.totalCount).isEqualTo(20);
+  }
+
+  @Test
+  public void onScrolled_withLinearLayoutManager_countsVisibleItems() {
+    Context context = ApplicationProvider.getApplicationContext();
+    RecyclerView recyclerView = newRecyclerViewWithAdapter(20);
+    recyclerView.setLayoutManager(new TestLinearLayoutManager(context, 2, 5));
+    RecordingOnScrollListener scrollListener = new RecordingOnScrollListener();
+    RecyclerToListViewScrollListener listener =
+        new RecyclerToListViewScrollListener(scrollListener);
+
+    listener.onScrolled(recyclerView, /* dx= */ 0, /* dy= */ 5);
+
+    assertThat(scrollListener.firstVisible).isEqualTo(2);
+    assertThat(scrollListener.visibleCount).isEqualTo(4);
+    assertThat(scrollListener.totalCount).isEqualTo(20);
+  }
+
+  private static RecyclerView newRecyclerViewWithAdapter(int itemCount) {
+    Context context = ApplicationProvider.getApplicationContext();
+    RecyclerView recyclerView = new RecyclerView(context);
+    recyclerView.setAdapter(new TestAdapter(itemCount));
+    return recyclerView;
+  }
+
+  private static final class RecordingOnScrollListener implements AbsListView.OnScrollListener {
+    int callCount;
+    int firstVisible;
+    int visibleCount;
+    int totalCount;
+
+    @Override
+    public void onScrollStateChanged(AbsListView view, int scrollState) {}
+
+    @Override
+    public void onScroll(
+        AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
+      callCount++;
+      firstVisible = firstVisibleItem;
+      visibleCount = visibleItemCount;
+      totalCount = totalItemCount;
+    }
+  }
+
+  private static final class FixedPositionProvider implements RecyclerViewPositionProvider {
+    private final int firstVisible;
+    private final int visibleCount;
+
+    FixedPositionProvider(int firstVisible, int visibleCount) {
+      this.firstVisible = firstVisible;
+      this.visibleCount = visibleCount;
+    }
+
+    @Override
+    public int getFirstVisiblePosition(@NonNull RecyclerView recyclerView) {
+      return firstVisible;
+    }
+
+    @Override
+    public int getVisibleItemCount(@NonNull RecyclerView recyclerView) {
+      return visibleCount;
+    }
+  }
+
+  private static final class TestLinearLayoutManager extends LinearLayoutManager {
+    private final int firstVisible;
+    private final int lastVisible;
+
+    TestLinearLayoutManager(Context context, int firstVisible, int lastVisible) {
+      super(context);
+      this.firstVisible = firstVisible;
+      this.lastVisible = lastVisible;
+    }
+
+    @Override
+    public int findFirstVisibleItemPosition() {
+      return firstVisible;
+    }
+
+    @Override
+    public int findLastVisibleItemPosition() {
+      return lastVisible;
+    }
+  }
+
+  private static final class TestAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
+    private final int itemCount;
+
+    TestAdapter(int itemCount) {
+      this.itemCount = itemCount;
+    }
+
+    @NonNull
+    @Override
+    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
+      return new RecyclerView.ViewHolder(new View(parent.getContext())) {};
+    }
+
+    @Override
+    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {}
+
+    @Override
+    public int getItemCount() {
+      return itemCount;
+    }
+  }
+}