RecyclerView存在大量Item时,当滚到底部时快速滑到顶部

  在使用RecyclerView展示图片或者其他信息时，往往需要展示很多的Item,当滚到底部时又想回到顶部，如果一点一点的向上划去比较麻烦，而且用户体验不好。因此添加一个快速回到顶部的按钮是很有必要的，并且刚开始的时候这个按钮是隐藏的，当滑动超过超过一屏的时候才会出现，在滑动的过程中也是不会出现的。很多类似的项目都会使用到，但是如何在快速回到顶部的过程中不出现卡顿，体现的很是流畅，这点很重要。下面是我根据网上的方法自己修改的一个可以快速回到顶部的类，在此做一下备注，以便日后查看：

1. FastScrollManger.java

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;import android.util.DisplayMetrics;/** * Author: aaa * Date: 2017/3/16 11:16. * 快速回到RecyclerView 的顶部,不会出现卡顿 */public class FastScrollManger extends LinearLayoutManager {    public FastScrollLinearLayoutManager(Context context) {        super(context);    }    public FastScrollLinearLayoutManager(Context context, int orientation, boolean reverseLayout) {        super(context, orientation, reverseLayout);    }    @Override    public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {        LinearSmoothScroller linearSmoothScroller = new LinearSmoothScroller(recyclerView.getContext()) {            @Override            public PointF computeScrollVectorForPosition(int targetPosition) {                return FastScrollLinearLayoutManager.this.computeScrollVectorForPosition(targetPosition);            }            //控制速度。            @Override            protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {                return super.calculateSpeedPerPixel(displayMetrics);            }            @Override            protected int calculateTimeForScrolling(int dx) {                if (dx > 3000) {                    dx = 3000;                }                int time = super.calculateTimeForScrolling(dx);                return time;            }        };        linearSmoothScroller.setTargetPosition(position);        startSmoothScroll(linearSmoothScroller);    }}

2.使用

mRecyclerView = (RecyclerView) findViewById(R.id.activity_recyclerview);        LinearLayoutManager layout = new FastScrollManager(CustomActivity.this, LinearLayoutManager.VERTICAL, false);        mRecyclerView.setLayoutManager(layout);//竖直放置        ...        mRecyclerView.setAdapter(mMyAdapter);        mRecyclerView.addOnScrollListener(new MyRecyclerViewScrollListener());

3.控制显示与隐藏

//滑动监听    private class MyRecyclerViewScrollListener extends RecyclerView.OnScrollListener {        @Override        public void onScrollStateChanged(RecyclerView recyclerView, int newState) {            super.onScrollStateChanged(recyclerView, newState);            LinearLayoutManager manager = (LinearLayoutManager) recyclerView.getLayoutManager();            int firstVisibleItemPosition = manager.findFirstVisibleItemPosition();            // 当不滚动时            if (newState == RecyclerView.SCROLL_STATE_IDLE) {                // 判断是否滚动超过一屏                if (firstVisibleItemPosition == 0) {                    mImageViewRebackTop.setVisibility(View.INVISIBLE);                } else {                    mImageViewRebackTop.setVisibility(View.VISIBLE);                }            } else if (newState == RecyclerView.SCROLL_STATE_DRAGGING) {//拖动中                mImageViewRebackTop.setVisibility(View.INVISIBLE);            }        }    }

4.点击回到顶部按钮的时候，回到顶部

mRecyclerView.smoothScrollToPosition(0);