一、CoordinatorLayout返回頂部：

 CoordinatorLayout.Behavior behavior =
                ((CoordinatorLayout.LayoutParams) indexAppBar.getLayoutParams()).getBehavior();
        if (behavior instanceof AppBarLayout.Behavior) {
            AppBarLayout.Behavior appBarLayoutBehavior = (AppBarLayout.Behavior) behavior;
 

            int topAndBottomOffset = appBarLayoutBehavior.getTopAndBottomOffset();
            if (topAndBottomOffset != 0) {
                appBarLayoutBehavior.setTopAndBottomOffset(0);
            }
        }

二、RecyclerView返回頂部

 recyclerView.scrollToPosition(0);

注：CoordinatorLayout一定要和AppBarLayout一起使用喲