RecyclerView指定された場所を画面の中央にスクロール

背景
製品の要求を受けて、RecyclerViewにitemをクリックしてからRecyclerViewの中間位置にスクロールさせる必要があります.
構想
LayoutManagerのカスタマイズ

カスタムSmoothScroller継承LinearSmoothScroller

LinearLayoutManagerを継承smoothScrollToPositionコールカスタムSmoothScroller

を書き換える

calculateDtToFitメソッドにおけるint viewStart,int viewEnd,int boxStart,int boxEndの意味計算スクロール位置の下に抜粋した部分LinearSmoothScrollerのソースコード

があることを明らかにする.

//LinearSmoothScroller     calculateDtToFit     
//top = item view   
final int top = layoutManager.getDecoratedTop(view) - params.topMargin;
//bottom = item view   
final int bottom = layoutManager.getDecoratedBottom(view) + params.bottomMargin;
//start = RecyclerView    
final int start = layoutManager.getPaddingTop();
//end = RecyclerView    
final int end = layoutManager.getHeight() - layoutManager.getPaddingBottom();
return calculateDtToFit(top, bottom, start, end, snapPreference);

インプリメンテーション

import android.content.Context;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.LinearSmoothScroller;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
import android.util.DisplayMetrics;

public class CenterLinearLayoutManager extends LinearLayoutManager {

    public CenterLinearLayoutManager(Context context) {
        super(context);
    }

    public CenterLinearLayoutManager(Context context, int orientation, boolean reverseLayout) {
        super(context, orientation, reverseLayout);
    }

    public CenterLinearLayoutManager(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }

    @Override
    public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {
        RecyclerView.SmoothScroller smoothScroller = new CenterSmoothScroller(recyclerView.getContext());
        smoothScroller.setTargetPosition(position);
        startSmoothScroll(smoothScroller);
    }

    private static class CenterSmoothScroller extends LinearSmoothScroller {

        public CenterSmoothScroller(Context context) {
            super(context);
        }

		//    
        @Override
        public int calculateDtToFit(int viewStart, int viewEnd, int boxStart, int boxEnd, int snapPreference) {
            return (boxStart + (boxEnd - boxStart) / 2) - (viewStart + (viewEnd - viewStart) / 2);
        }

		//    
        @Override
        protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
            return 100f / displayMetrics.densityDpi;
        }

    }

}

使用
RecyclerViewのLayoutManagerを切り替えるだけ

mListView.setLayoutManager(new CenterLinearLayoutManager(getContext(), LinearLayoutManager.HORIZONTAL, false));