安卓当下最流行的吸顶效果的实现（下）

安卓开发精选 · 公众号 · android · 2017-01-12 21:12

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来源：李诗雨
http://blog.csdn.net/cjm2484836553/article/details/53453982
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接上文

第一步：首先我们来写一个类，它起标记的作用，来放每一个item的对应的悬浮栏的字符串

public class NameBean {
    String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

第二步：自定义一个SectionDecoration 类继承 RecyclerView的ItemDecoration

public class SectionDecoration extends RecyclerView.ItemDecoration {
    private static final String TAG = "SectionDecoration";

    private List dataList;

    private DecorationCallback callback;
    private TextPaint textPaint;
    private Paint paint;
    private int topGap;
    private int alignBottom;
    private Paint.FontMetrics fontMetrics;


    public SectionDecoration(List dataList, Context context, DecorationCallback decorationCallback) {
        Resources res = context.getResources();
        this.dataList = dataList;
        this.callback = decorationCallback;
        //设置悬浮栏的画笔---paint
        paint = new Paint();
        paint.setColor(res.getColor(R.color.colorGray));

        //设置悬浮栏中文本的画笔
        textPaint = new TextPaint();
        textPaint.setAntiAlias(true);
        textPaint.setTextSize(DensityUtil.dip2px(context, 14));
        textPaint.setColor(Color.DKGRAY);
        textPaint.setTextAlign(Paint.Align.LEFT);
        fontMetrics = new Paint.FontMetrics();
        //决定悬浮栏的高度等
        topGap = res.getDimensionPixelSize(R.dimen.sectioned_top);
        //决定文本的显示位置等
        alignBottom = res.getDimensionPixelSize(R.dimen.sectioned_alignBottom);
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        int pos = parent.getChildAdapterPosition(view);
        Log.i(TAG, "getItemOffsets：" + pos);
        String groupId = callback.getGroupId(pos);
        if (groupId.equals("-1")) return;
        //只有是同一组的第一个才显示悬浮栏
        if (pos == 0 || isFirstInGroup(pos)) {
            outRect.top = topGap;
            if (dataList.get(pos).getName() == "") {
                outRect.top = 0;
            }
        } else {
            outRect.top = 0;
        }
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDraw(c, parent, state);
        int left = parent.getPaddingLeft();
        int right = parent.getWidth() - parent.getPaddingRight();
        int childCount = parent.getChildCount();
        for (int i = 0; i childCount; i++) {
            View view = parent.getChildAt(i);
            int position = parent.getChildAdapterPosition(view);
            String groupId = callback.getGroupId(position);
            if (groupId.equals("-1")) return;
            String textLine = callback.getGroupFirstLine(position).toUpperCase();
            if (textLine == "") {
                float top = view.getTop();
                float bottom = view.getTop();
                c.drawRect(left, top, right, bottom, paint);
                return;
            } else {
                if (position == 0 || isFirstInGroup(position)) {
                    float top = view.getTop() - topGap;
                    float bottom = view.getTop();
                    //绘制悬浮栏
                    c.drawRect(left, top - topGap, right, bottom, paint);
                    //绘制文本
                    c.drawText(textLine, left, bottom, textPaint);
                }
            }
        }
    }

    @Override
    public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDrawOver(c, parent, state);
        int itemCount = state.getItemCount();
        int childCount = parent.getChildCount();
        int left = parent.getPaddingLeft();
        int right = parent.getWidth() - parent.getPaddingRight();
        float lineHeight = textPaint.getTextSize() + fontMetrics.descent;

        String preGroupId = "";
        String 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.equals("-1") || groupId.equals(preGroupId)) continue;

            String textLine = callback.getGroupFirstLine(position).toUpperCase();
            if (TextUtils.isEmpty(textLine)) continue;

            int viewBottom = view.getBottom();
            float textY = Math.max(topGap, view.getTop());
            //下一个和当前不一样移动当前
            if (position + 1 itemCount) {
                String nextGroupId = callback.getGroupId(position + 1);
                //组内最后一个view进入了header
                if (nextGroupId != groupId && viewBottom textY) {
                    textY = viewBottom;
                }
            }
            //textY - topGap决定了悬浮栏绘制的高度和位置
            c.drawRect(left, textY - topGap, right, textY, paint);
            //left+2*alignBottom 决定了文本往左偏移的多少（加-->向左移）
            //textY-alignBottom  决定了文本往右偏移的多少  (减-->向上移)
            c.drawText(textLine, left + 2 * alignBottom, textY - alignBottom, textPaint);
        }
    }


    /**
     * 判断是不是组中的第一个位置
     *
     * @param pos
     * @return
     */
    private boolean isFirstInGroup(int pos) {
        if (pos == 0) {
            return true;
        } else {
            // 因为是根据字符串内容的相同与否来判断是不是同意组的，所以此处的标记id 要是String类型
            // 如果你只是做联系人列表，悬浮框里显示的只是一个字母，则标记id直接用 int 类型就行了
            String prevGroupId = callback.getGroupId(pos - 1);
            String groupId = callback.getGroupId(pos);
            //判断前一个字符串与当前字符串是否相同
            if (prevGroupId.equals(groupId)) {
                return false;
            } else {
                return true;
            }
        }
    }

    //定义一个借口方便外界的调用
    interface DecorationCallback {
        String getGroupId(int position);

        String getGroupFirstLine(int position);
    }
}

第三步：在向list集合中先把每一个item的起“标记”作用的字符串都加进去

setPullAction(comingslist);

private void setPullAction(ListWaitMVBean.DataBean.ComingBean> comingslist) {
        dataList = new ArrayList();

        for (int i = 0; i comingslist.size(); i++) {
            NameBean nameBean = new NameBean();
            String name0 = comingslist.get(i).getComingTitle();
            nameBean.setName(name0);
            dataList.add(nameBean);
        }
    }

第四步：在setAdapter() 前，为RecyclerView添加ItemDecoration:

recyclerView.addItemDecoration(new SectionDecoration(dataList,mContext, new SectionDecoration.DecorationCallback() {
               //返回标记id (即每一项对应的标志性的字符串)
                @Override
                public String getGroupId(int position) {
                    if(dataList.get(position).getName()!=null) {
                        return dataList.get(position).getName();
                    }
                    return "-1";
                }

                //获取同组中的第一个内容
                @Override
                public String getGroupFirstLine(int position) {
                    if(dataList.get(position).getName()!=null) {
                        return dataList.get(position).getName();
                    }
                    return "";
                }
            }));

这样就完成了~

再看一眼最终效果感受一下：

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