RecyclerView选中项居中(横向、竖向)，指定位置置顶（竖向）

需要实现对LinearLayoutManager的重写

中间显示类

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.DisplayMetrics;

public class CenterLayoutManager extends LinearLayoutManager {

    static int lastPositon = 0;
    static int targetPosion = 0;

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

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

    public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int lastpositon, int position) {
        this.lastPositon = lastpositon;
        this.targetPosion = position;
        smoothScrollToPosition(recyclerView, state, position);
    }

    public static class CenterSmoothScroller extends LinearSmoothScroller {

        private static float duration = 800f;//显示到中间的动画时长

        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) {
            float newDuration = duration / (Math.abs(targetPosion - lastPositon));//重新计算相近两个位置的滚动间隔
            return newDuration / displayMetrics.densityDpi;
        }

        @Override
        protected int calculateTimeForScrolling(int dx) {
            return super.calculateTimeForScrolling(dx);
        }

    }
}

置顶显示类

import android.content.Context;
import android.graphics.PointF;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.LinearSmoothScroller;
import android.support.v7.widget.RecyclerView;

public class TopLinearLayoutManager extends LinearLayoutManager {

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

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

    private class TopSnappedSmoothScroller extends LinearSmoothScroller {
        public TopSnappedSmoothScroller(Context context) {
            super(context);

        }

        @Override
        public PointF computeScrollVectorForPosition(int targetPosition) {
            return TopLinearLayoutManager.this
                    .computeScrollVectorForPosition(targetPosition);
        }

        @Override
        protected int getVerticalSnapPreference() {
            return SNAP_TO_START;
        }
    }
}

调用方法，按需采用

//初始化置顶
TopLinearLayoutManager topLinearLayoutManager = new TopLinearLayoutManager(getContext(), 
LinearLayoutManager.VERTICAL, false);
//初始化中间竖向
CenterLayoutManager centerLayoutManager = new CenterLayoutManager(getContext(), LinearLayoutManager.VERTICAL, false);
//初始化中间横向
CenterLayoutManager centerLayoutManager = new CenterLayoutManager(getContext(), LinearLayoutManager.HORIZONTAL, false);
//绑定置顶
mRecyclerView.setLayoutManager(topLinearLayoutManager);
//绑定中间
mRecyclerView.setLayoutManager(centerLayoutManager );

//置顶显示调用
mRecyclerView.smoothScrollToPosition(position);
//中间显示调用 lastPostion是临时保存的目前处在中间的position
centerLayoutManager.smoothScrollToPosition(mRecyclerView, new RecyclerView.State(), lastPostion, position);
        //记住当前选中的位置作为下一次选中的位置的上一次位置
        if (lastPostion != position)
            lastPostion = position;

 

本文地址：https://blog.csdn.net/u011652925/article/details/110957247