利用ItemDecoration给RecyclerView的item添加标题

先看效果

/* * Created by IT小蔡 on 17-7-19 下午4:14 * Copyright (c) 2017. All right reserved * * Last modified 17-7-19 下午4:14 */package cyk.com.doublegangedrecyclerview.itemdecoration;import android.content.Context;import android.content.res.Resources;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.graphics.Rect;import android.graphics.Typeface;import android.support.v7.widget.RecyclerView;import android.text.TextPaint;import android.text.TextUtils;import android.util.Log;import android.view.View;import cyk.com.doublegangedrecyclerview.R;/** * Created by admin on 2017-7-19. */public class StickyItemDescoration extends RecyclerView.ItemDecoration {    private static final String TAG = "PinnedSectionDecoration";    private DecorationCallback callback;    private TextPaint textPaint;    private Paint paint;    private int topGap;    public StickyItemDescoration(Context context, DecorationCallback decorationCallback) {        Resources res = context.getResources();        this.callback = decorationCallback;        paint = new Paint();        paint.setColor(res.getColor(R.color.colorAccent));        textPaint = new TextPaint();        textPaint.setTypeface(Typeface.DEFAULT_BOLD);        textPaint.setAntiAlias(true);        textPaint.setTextSize(80);        textPaint.setColor(Color.BLACK);        textPaint.setTextAlign(Paint.Align.LEFT);        topGap = res.getDimensionPixelSize(R.dimen.sectioned_top);    }    @Override    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {        super.getItemOffsets(outRect, view, parent, state);        int pos = parent.getChildAdapterPosition(view);        long groupId = callback.getGroupId(pos);        if (groupId < 0) return;        if (pos == 0 || isFirstInGroup(pos)) {            outRect.top = topGap;        } else {            outRect.top = 0;        }    }    @Override    public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {        Log.e(TAG, "onDrawOver: " );        super.onDrawOver(c, parent, state);        int childCount = parent.getChildCount(); //获得可见的item数量        int itemCount = parent.getAdapter().getItemCount();//获得所有item数量        int left = parent.getPaddingLeft();        int right = parent.getWidth() - parent.getPaddingRight();        long preGroupId, groupId = -1;        for (int i = 0; i < childCount; i++) {            View view = parent.getChildAt(i);            int position = parent.getChildAdapterPosition(view);            preGroupId = groupId;            groupId = callback.getGroupId(position);            if (groupId < 0 || groupId == preGroupId) continue;            String textLine = callback.getGroupFirstLine(position).toUpperCase();            if (TextUtils.isEmpty(textLine)) continue;           int viewBottom = view.getBottom();//此时view底部的距离            float textY = Math.max(topGap, view.getTop());            if (position + 1 < itemCount) { //下一个和当前不一样移动当前                long nextGroupId = callback.getGroupId(position + 1);                if (nextGroupId != groupId && viewBottom < textY ) {//组内最后一个view进入了header                    textY = viewBottom;                }            }            c.drawRect(left, textY - topGap, right, textY, paint);            Rect rect = new Rect();            textPaint.getTextBounds(textLine,0,textLine.length(),rect);            c.drawText(textLine, view.getWidth()/2-rect.width()/2, textY-(topGap-rect.height())/2, textPaint);//绘制居中标题        }    }    private boolean isFirstInGroup(int pos) {        if (pos == 0) {            return true;        } else {            long prevGroupId = callback.getGroupId(pos - 1);            long groupId = callback.getGroupId(pos);            return prevGroupId != groupId;        }    }    public interface DecorationCallback {        long getGroupId(int position);        String getGroupFirstLine(int position);    }}

recycleView.addItemDecoration(new DividerItemDecoration(mContext,DividerItemDecoration.VERTICAL));//下划线可以叠加

recycleView.addItemDecoration(new StickyItemDescoration(mContext, new StickyItemDescoration.DecorationCallback() {            @Override            public long getGroupId(int position) {                return Character.toUpperCase(list.get(position).charAt(0));            }            @Override            public String getGroupFirstLine(int position) {                return list.get(position).substring(0, 1).toUpperCase();            }        }));