support smooth scrolling with offset

Summary: Can smooth scroll to child with an added offset

Reviewed By: astreet

Differential Revision: D8682952

fbshipit-source-id: 334406f81d4cb6681442e5648d0c87cffe3967bd

litho-sections-core/src/main/java/com/facebook/litho/sections/BatchedTarget.java

@@ -153,8 +153,8 @@ public void requestFocus(int index) {
   }
 
   @Override
-  public void requestSmoothFocus(int index, SmoothScrollAlignmentType type) {
-    mTarget.requestSmoothFocus(index, type);
+  public void requestSmoothFocus(int index, int offset, SmoothScrollAlignmentType type) {
+    mTarget.requestSmoothFocus(index, offset, type);
     maybeLogRequestFocus(index);
   }
 

litho-sections-core/src/main/java/com/facebook/litho/sections/FocusDispatcher.java

@@ -53,9 +53,9 @@ void requestFocus(int index) {
   }
 
   @UiThread
-  void requestSmoothFocus(int index, SmoothScrollAlignmentType type) {
+  void requestSmoothFocus(int index, int offset, SmoothScrollAlignmentType type) {
     if (shouldDispatchRequests()) {
-      mTarget.requestSmoothFocus(index, type);
+      mTarget.requestSmoothFocus(index, offset, type);
       return;
     }
 

litho-sections-core/src/main/java/com/facebook/litho/sections/SectionLifecycle.java

@@ -373,16 +373,16 @@ public static void requestFocusWithOffset(
   }
 
   public static void requestSmoothFocus(SectionContext c, int index) {
-    requestSmoothFocus(c, "", index, SmoothScrollAlignmentType.DEFAULT);
+    requestSmoothFocus(c, "", index, 0, SmoothScrollAlignmentType.DEFAULT);
   }
 
   public static void requestSmoothFocus(
       SectionContext c, int index, SmoothScrollAlignmentType type) {
-    requestSmoothFocus(c, "", index, type);
+    requestSmoothFocus(c, "", index, 0, type);
   }
 
   public static void requestSmoothFocus(
-      SectionContext c, String keyString, int index, SmoothScrollAlignmentType type) {
+      SectionContext c, String keyString, int index, int offset, SmoothScrollAlignmentType type) {
     final Section scopedSection = c.getSectionScope();
     final SectionTree sectionTree = c.getSectionTree();
 
@@ -391,6 +391,6 @@ public static void requestSmoothFocus(
     }
 
     final String globalKey = scopedSection.getGlobalKey() + keyString;
-    sectionTree.requestSmoothFocus(globalKey, index, type);
+    sectionTree.requestSmoothFocus(globalKey, index, offset, type);
   }
 }

litho-sections-core/src/main/java/com/facebook/litho/sections/SectionTree.java

@@ -127,7 +127,7 @@ public interface Target {
     void requestFocus(int index);
 
     /** Request smooth focus on the item with the given index. */
-    void requestSmoothFocus(int index, SmoothScrollAlignmentType type);
+    void requestSmoothFocus(int index, int offset, SmoothScrollAlignmentType type);
 
     /**
      * Request focus on the item with the given index, plus some additional offset.
@@ -661,14 +661,18 @@ public void run() {
   }
 
   void requestSmoothFocus(
-      final String globalKey, final int index, final SmoothScrollAlignmentType type) {
+      final String globalKey,
+      final int index,
+      final int offset,
+      final SmoothScrollAlignmentType type) {
     focusRequestOnUiThread(
         new Runnable() {
           @Override
           public void run() {
             final SectionLocationInfo sectionLocationInfo = findSectionForKey(globalKey);
             checkFocusValidity(sectionLocationInfo, index);
-            mFocusDispatcher.requestSmoothFocus(sectionLocationInfo.mStartIndex + index, type);
+            mFocusDispatcher.requestSmoothFocus(
+                sectionLocationInfo.mStartIndex + index, offset, type);
           }
         });
   }

litho-sections-widget/src/main/java/com/facebook/litho/sections/widget/SectionBinderTarget.java

@@ -150,8 +150,8 @@ public void requestFocus(int index) {
   }
 
   @Override
-  public void requestSmoothFocus(int index, SmoothScrollAlignmentType type) {
-    mRecyclerBinder.scrollSmoothToPosition(index, type);
+  public void requestSmoothFocus(int index, int offset, SmoothScrollAlignmentType type) {
+    mRecyclerBinder.scrollSmoothToPosition(index, offset, type);
   }
 
   @Override

litho-testing/src/main/java/com/facebook/litho/testing/sections/TestTarget.java

@@ -133,7 +133,7 @@ public void requestFocus(int index) {
   }
 
   @Override
-  public void requestSmoothFocus(int index, SmoothScrollAlignmentType type) {
+  public void requestSmoothFocus(int index, int offset, SmoothScrollAlignmentType type) {
     requestFocus(index);
   }
 

litho-widget/src/main/java/com/facebook/litho/widget/RecyclerBinder.java

@@ -2301,9 +2301,11 @@ public void scrollToPosition(int position) {
   }
 
   @UiThread
-  public void scrollSmoothToPosition(int position, final SmoothScrollAlignmentType type) {
+  public void scrollSmoothToPosition(
+      int position, final int offset, final SmoothScrollAlignmentType type) {
     if (mMountedView == null) {
       mCurrentFirstVisiblePosition = position;
+      mCurrentOffset = offset;
       return;
     }
 
@@ -2313,11 +2315,20 @@ public void scrollSmoothToPosition(int position, final SmoothScrollAlignmentType
         || type == SmoothScrollAlignmentType.SNAP_TO_END) {
       RecyclerView.SmoothScroller selectedSmoothScroller =
           new LinearSmoothScroller(mComponentContext) {
+            @Override
+            public int calculateDtToFit(
+                int viewStart, int viewEnd, int boxStart, int boxEnd, int snapPreference) {
+              int result =
+                  super.calculateDtToFit(viewStart, viewEnd, boxStart, boxEnd, snapPreference);
+              return result + offset;
+            }
+
             @Override
             protected int getVerticalSnapPreference() {
               return representation;
             }
 
+            @Override
             protected int getHorizontalSnapPreference() {
               return representation;
             }