[Carousel] Implemented smoothScrollToPosition

PiperOrigin-RevId: 509873609

Author: hunterstich

catalog/java/io/material/catalog/carousel/MultiBrowseDemoFragment.java

@@ -30,6 +30,8 @@
 import com.google.android.material.carousel.MultiBrowseCarouselStrategy;
 import com.google.android.material.divider.MaterialDividerItemDecoration;
 import com.google.android.material.materialswitch.MaterialSwitch;
+import com.google.android.material.slider.Slider;
+import com.google.android.material.slider.Slider.OnSliderTouchListener;
 import io.material.catalog.feature.DemoFragment;
 
 /** A fragment that displays the multi-browse variants of the Carousel. */
@@ -60,6 +62,7 @@ public void onViewCreated(@NonNull View view, @Nullable Bundle bundle) {
     MaterialSwitch forceCompactSwitch = view.findViewById(R.id.force_compact_arrangement_switch);
     MaterialSwitch drawDividers = view.findViewById(R.id.draw_dividers_switch);
     AutoCompleteTextView itemCountDropdown = view.findViewById(R.id.item_count_dropdown);
+    Slider positionSlider = view.findViewById(R.id.position_slider);
 
     // A start-aligned multi-browse carousel
     RecyclerView multiBrowseStartRecyclerView =
@@ -97,10 +100,38 @@ public void onViewCreated(@NonNull View view, @Nullable Bundle bundle) {
             (item, position) -> multiBrowseStartRecyclerView.scrollToPosition(position));
 
     itemCountDropdown.setOnItemClickListener(
-        (parent, view1, position, id) ->
-            adapter.submitList(CarouselData.createItems().subList(0, position)));
+        (parent, view1, position, id) -> {
+          adapter.submitList(
+              CarouselData.createItems().subList(0, position),
+              updateSliderRange(positionSlider, adapter));
+        });
+
+    positionSlider.addOnSliderTouchListener(
+        new OnSliderTouchListener() {
+          @Override
+          public void onStartTrackingTouch(@NonNull Slider slider) {}
+
+          @Override
+          public void onStopTrackingTouch(@NonNull Slider slider) {
+            multiBrowseStartRecyclerView.smoothScrollToPosition((int) slider.getValue() - 1);
+          }
+        });
 
     multiBrowseStartRecyclerView.setAdapter(adapter);
-    adapter.submitList(CarouselData.createItems());
+    adapter.submitList(CarouselData.createItems(), updateSliderRange(positionSlider, adapter));
+  }
+
+  private static Runnable updateSliderRange(Slider slider, CarouselAdapter adapter) {
+    return () -> {
+      if (adapter.getItemCount() == 0) {
+        slider.setValueFrom(0);
+        slider.setValueTo(0);
+        return;
+      }
+
+      slider.setValue(1);
+      slider.setValueFrom(1);
+      slider.setValueTo(adapter.getItemCount());
+    };
   }
 }

catalog/java/io/material/catalog/carousel/res/layout/cat_carousel_multi_browse_fragment.xml

@@ -88,6 +88,25 @@
 
     </com.google.android.material.textfield.TextInputLayout>
 
+    <TextView
+      android:id="@+id/position_slider_label"
+      android:layout_width="wrap_content"
+      android:layout_height="wrap_content"
+      android:layout_marginHorizontal="16dp"
+      android:layout_marginTop="16dp"
+      android:labelFor="@id/position_slider"
+      android:text="@string/cat_carousel_position_slider_label"
+      android:textAppearance="?attr/textAppearanceBodyLarge"/>
+
+    <com.google.android.material.slider.Slider
+      android:id="@+id/position_slider"
+      android:layout_width="match_parent"
+      android:layout_height="wrap_content"
+      android:layout_marginHorizontal="16dp"
+      android:layout_marginBottom="8dp"
+      android:contentDescription="@string/cat_carousel_position_slider_content_description"
+      android:stepSize="1.0"/>
+
     <androidx.recyclerview.widget.RecyclerView
       android:id="@+id/multi_browse_start_carousel_recycler_view"
       android:layout_width="match_parent"

catalog/java/io/material/catalog/carousel/res/values/strings.xml

@@ -20,6 +20,8 @@
   <string name="cat_carousel_force_compact_arrangement_label" translatable="false">Force compact arrangement</string>
   <string name="cat_carousel_draw_dividers_label" translatable="false">Draw dividers</string>
   <string name="cat_carousel_adapter_item_count_hint_label" translatable="false">Item count</string>
+  <string name="cat_carousel_position_slider_label" translatable="false">Scroll position</string>
+  <string name="cat_carousel_position_slider_content_description" translatable="false">Scroll position slider</string>
 
   <string-array name="cat_carousel_adapter_count_content" translatable="false">
     <item>0</item>

lib/java/com/google/android/material/carousel/CarouselLayoutManager.java

@@ -25,7 +25,9 @@
 import android.graphics.Canvas;
 import android.graphics.Color;
 import android.graphics.Paint;
+import android.graphics.PointF;
 import android.graphics.Rect;
+import androidx.recyclerview.widget.LinearSmoothScroller;
 import androidx.recyclerview.widget.RecyclerView;
 import androidx.recyclerview.widget.RecyclerView.LayoutManager;
 import androidx.recyclerview.widget.RecyclerView.LayoutParams;
@@ -806,6 +808,35 @@ public void scrollToPosition(int position) {
     requestLayout();
   }
 
+  @Override
+  public void smoothScrollToPosition(RecyclerView recyclerView, State state, int position) {
+    LinearSmoothScroller linearSmoothScroller =
+        new LinearSmoothScroller(recyclerView.getContext()) {
+          @Nullable
+          @Override
+          public PointF computeScrollVectorForPosition(int targetPosition) {
+            if (keylineStateList == null) {
+              return null;
+            }
+
+            float targetScrollOffset =
+                getScrollOffsetForPosition(keylineStateList.getDefaultState(), targetPosition);
+            return new PointF(targetScrollOffset - horizontalScrollOffset, 0F);
+          }
+
+          @Override
+          public int calculateDxToMakeVisible(View view, int snapPreference) {
+            // Override dx calculations so the target view is brought all the way into the focal
+            // range instead of just being made visible.
+            float targetScrollOffset =
+                getScrollOffsetForPosition(keylineStateList.getDefaultState(), getPosition(view));
+            return (int) (horizontalScrollOffset - targetScrollOffset);
+          }
+        };
+    linearSmoothScroller.setTargetPosition(position);
+    startSmoothScroll(linearSmoothScroller);
+  }
+
   @Override
   public boolean canScrollHorizontally() {
     return true;