Android recyclerView的使用

1.添加依赖 api 'com.android.support:recyclerview-v7:27.1.1'
2.构建适配器（适配器getItemCount的数量一定要大于0）

public class BeautyAdapter extends RecyclerView.Adapter<BeautyAdapter.BeautyViewHolder> {
    private List<BeautyRes.ResultsBean> mDatas;
    private Context mContext;
    private int layout;
    public BeautyAdapter(List<BeautyRes.ResultsBean> mDatas, Context mContext, int layout) {
        this.mDatas = mDatas;
        this.mContext = mContext;
        this.layout=layout;
    }
    @NonNull
    @Override
    public BeautyAdapter.BeautyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View inflateView = LayoutInflater.from(mContext).inflate(layout, parent, false);
        BeautyAdapter.BeautyViewHolder beautyViewHolder=new BeautyAdapter.BeautyViewHolder(inflateView);
        return beautyViewHolder;
    }

    @Override
    public void onBindViewHolder(@NonNull BeautyAdapter.BeautyViewHolder holder, int position) {
        String url = mDatas.get(position).getUrl();
        Glide.with(mContext).load(url).into(holder.imageView);
    }

    @Override
    public int getItemCount() {
        return mDatas.size();
    }
    public static class BeautyViewHolder extends RecyclerView.ViewHolder{
        private ImageView imageView;
        public BeautyViewHolder(View itemView) {
            super(itemView);
            imageView=itemView.findViewById(R.id.social_chat_bg_iv);
        }
    }
}
2.自定义分割线
  第一步：
        因为是瀑布流所以先画一个横竖的正方形
        <?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle">
<size
   android:width="2dp"
  android:height="2dp" />
</shape>
第二步:
在系统的recyclerView属性中添加style<item name="android:listDivider">@drawable/divider_shape</item>第三步：
  因为RecyclerView不想ListView一样所以需要自己编写分割线

package com.dejun.commonsdk.wight;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.StaggeredGridLayoutManager;
import android.view.View;

/**
 * Author:DoctorWei
 * Time:2018/12/8 18:22
 * Description:
 * email:[email protected]
 */

public class StaggeredDividerItemDecoration extends RecyclerView.ItemDecoration {
    private int[] attrs = new int[]{
            android.R.attr.listDivider
    };
    public static final int DIRECTION_VERTICAL = 0;
    public static final int DIRECTION_HORIZONTAL = 1;
    private Drawable divider;
    private int direction;
    private final int column;

    public StaggeredDividerItemDecoration(Context context, int direction, int column) {
        super();
        TypedArray typedArray = context.obtainStyledAttributes(attrs);
        divider = typedArray.getDrawable(0);
        this.direction = direction;
        this.column = column;
    }


    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        System.out.println("onDraw" + state.toString());
        super.onDraw(c, parent, state);
        if (divider == null)
            return;
        if (direction == DIRECTION_VERTICAL) {
            drawVerticalDivider(c, parent);
        } else {
            drawHoriziontalDivider(c, parent);
        }
    }

    private void drawHoriziontalDivider(Canvas c, RecyclerView parent) {
        int left = 0;
        int top = 0;
        int right = 0;
        int bottom = 0;
        for (int i = 0; i < parent.getChildCount(); i++) {
            View child = parent.getChildAt(i);
            int position = ((StaggeredGridLayoutManager.LayoutParams) child.getLayoutParams()).getSpanIndex();
            RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) child.getLayoutParams();

            //头部第一条线
            if (position == 0) {
                top = child.getTop() - layoutParams.topMargin - divider.getIntrinsicHeight();
                bottom = top + divider.getIntrinsicHeight();
                left = child.getLeft() - layoutParams.leftMargin;
                right = child.getRight() + layoutParams.rightMargin;
                divider.setBounds(left, top, right, bottom);
                divider.draw(c);
            }
            //最右边的线
            if (i >= parent.getChildCount() - column) {
                top = child.getTop() - layoutParams.topMargin - divider.getIntrinsicHeight();
                bottom = child.getBottom() + layoutParams.bottomMargin + divider.getIntrinsicHeight();
                left = child.getRight() + layoutParams.rightMargin;
                right = left + divider.getIntrinsicWidth();
                divider.setBounds(left, top, right, bottom);
                divider.draw(c);
            }
            //最后一个补线
            if(i>=parent.getChildCount()-column&&position!=0){
                top = child.getTop() - layoutParams.topMargin - divider.getIntrinsicHeight();
                bottom = top + divider.getIntrinsicHeight();
                left = child.getLeft() - layoutParams.leftMargin;
                right = child.getRight() + layoutParams.rightMargin;
                divider.setBounds(left, top, right, bottom);
                divider.draw(c);

            }
            //左边的线
            top = child.getTop() - layoutParams.topMargin - divider.getIntrinsicHeight();
            bottom = child.getBottom() + layoutParams.bottomMargin + divider.getIntrinsicHeight();
            left = child.getLeft() - layoutParams.leftMargin - divider.getIntrinsicWidth();
            right = left + divider.getIntrinsicWidth();
            divider.setBounds(left, top, right, bottom);
            divider.draw(c);

            //下面的线
            top = child.getBottom() + layoutParams.bottomMargin;
            bottom = top + divider.getIntrinsicHeight();
            left = child.getLeft() - layoutParams.leftMargin;
            right = child.getRight() + layoutParams.rightMargin;
            divider.setBounds(left, top, right, bottom);
            divider.draw(c);
        }

    }


    private void drawVerticalDivider(Canvas c, RecyclerView parent) {
        int left = 0;
        int top = 0;
        int right = 0;
        int bottom = 0;
        for (int i = 0; i < parent.getChildCount(); i++) {
            View child = parent.getChildAt(i);
            RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) child.getLayoutParams();
            int position = ((StaggeredGridLayoutManager.LayoutParams) child.getLayoutParams()).getSpanIndex();
            //头部第一条线
            if (i / column == 0) {
                top = child.getTop() - layoutParams.topMargin - divider.getIntrinsicHeight();
                bottom = top + divider.getIntrinsicHeight();
                left = child.getLeft() - layoutParams.leftMargin;
                right = child.getRight() + layoutParams.rightMargin;
                divider.setBounds(left, top, right, bottom);
                divider.draw(c);
            }
            //最右边的线
            if (position == column - 1) {
                top = child.getTop() - layoutParams.topMargin - divider.getIntrinsicHeight();
                bottom = child.getBottom() + layoutParams.bottomMargin + divider.getIntrinsicHeight();
                left = child.getRight() + layoutParams.rightMargin;
                right = left + divider.getIntrinsicWidth();
                divider.setBounds(left, top, right, bottom);
                divider.draw(c);
            }
            //最后一个补线
            if (i>=parent.getChildCount()-column&&position!=2) {
                top = child.getTop() - layoutParams.topMargin - divider.getIntrinsicHeight();
                bottom = child.getBottom() + layoutParams.bottomMargin + divider.getIntrinsicHeight();
                left = child.getRight() + layoutParams.rightMargin;
                right = left + divider.getIntrinsicWidth();
                divider.setBounds(left, top, right, bottom);
                divider.draw(c);

            }
            //左边的线
            top = child.getTop() - layoutParams.topMargin - divider.getIntrinsicHeight();
            bottom = child.getBottom() + layoutParams.bottomMargin + divider.getIntrinsicHeight();
            left = child.getLeft() - layoutParams.leftMargin - divider.getIntrinsicWidth();
            right = left + divider.getIntrinsicWidth();
            divider.setBounds(left, top, right, bottom);
            divider.draw(c);

            //下面的线
            top = child.getBottom() + layoutParams.bottomMargin;
            bottom = top + divider.getIntrinsicHeight();
            left = child.getLeft() - layoutParams.leftMargin;
            right = child.getRight() + layoutParams.rightMargin;
            divider.setBounds(left, top, right, bottom);
            divider.draw(c);
        }
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        final StaggeredGridLayoutManager.LayoutParams slp = (StaggeredGridLayoutManager.LayoutParams) view.getLayoutParams();
        int p2 = slp.getSpanIndex();
        System.out.println("p2:" + p2);
        System.out.println("divider:" + divider.getIntrinsicHeight() + "  " + divider.getIntrinsicWidth());
        int p = parent.getChildAdapterPosition(view);
        int p1 = parent.getChildLayoutPosition(view);
        int left = 0;
        int top = 0;
        int right = 0;
        int bottom = 0;
        System.out.println("p:" + p + " p1:" + p1 + state.toString());
        if (direction == DIRECTION_VERTICAL) {
            int position = parent.getChildLayoutPosition(view);
            if (position / column == 0)
                top = divider.getIntrinsicHeight();
            if (p2 == column - 1) {
                right = divider.getIntrinsicWidth();
                System.out.println("p:p:p" + p);
            }
            left = divider.getIntrinsicWidth();
            bottom = divider.getIntrinsicHeight();
            outRect.set(left, top, right, bottom);
        } else {
            int position = parent.getChildLayoutPosition(view);
            if (position / column == 0)
                left = divider.getIntrinsicWidth();
            if (p2 == 0)
                top = divider.getIntrinsicHeight();
            right = divider.getIntrinsicWidth();
            bottom = divider.getIntrinsicHeight();
            outRect.set(left, top, right, bottom);
        }
    }
}3.创建布局管理器并设置适配器（一定要设置LayoutManager）
StaggeredGridLayoutManager staggeredGridLayoutManager = new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL);
staggeredGridLayoutManager.setGapStrategy(StaggeredGridLayoutManager.GAP_HANDLING_NONE);//优化图片闪烁和错位mBeautyRv.setLayoutManager(staggeredGridLayoutManager);
mBeautyRv.addItemDecoration(new StaggeredDividerItemDecoration(_mActivity,StaggeredDividerItemDecoration.DIRECTION_VERTICAL,2));
mBeautyRv.setAdapter(new BeautyAdapter(beautyRes.getResults(), _mActivity, R.layout.beauty_item_layout));