ItemDecoration实现stickyHeader效果

短命女 2023-01-23 01:05 114阅读 0赞

![在这里插入图片描述][20210520202246305.gif_pic_center]

/** * 快速选择器章节装饰 */
    public class FastIndexSectionDecoration extends RecyclerView.ItemDecoration { 
    
        private Context mContext;
        private List<FilterBean> mData;
    
        private int backgroundColor;
        private int textColor;
        private float textSize;
        private float textMarginLeft = 35;
        private int mDecorationHeight;
    
        private Paint mBgPaint;
        private Paint mTextPaint;
        private Rect mTextBounds;
    
        public FastIndexSectionDecoration(Context context, List<FilterBean> data) { 
            this.mContext = context;
            this.mData = data;
            backgroundColor = Color.parseColor("#66C2FFF1");
            textColor = Color.parseColor("#FF9999");
            textSize = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, 16, context.getResources().getDisplayMetrics());
    
            mTextPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
            mTextPaint.setTextSize(textSize);
            mTextPaint.setColor(textColor);
    
            mBgPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
            mBgPaint.setColor(backgroundColor);
    
            mDecorationHeight = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 35, context.getResources().getDisplayMetrics());
            mTextBounds = new Rect();
        }
    
    
        @Override
        public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) { 
            super.getItemOffsets(outRect, view, parent, state);
    
            if (mData == null || mData.size() == 0) { 
                return;
            }
    
            int position = ((RecyclerView.LayoutParams) view.getLayoutParams()).getViewAdapterPosition();
            if (position > mData.size() - 1 || position < 0) { 
                return;
            }
    
            // 第一个分类不需要显示分类章节
            if (position > 0 && !TextUtils.equals(mData.get(position).getFirstChar(), mData.get(position - 1).getFirstChar())) { 
                outRect.set(0, mDecorationHeight, 0, 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 child = parent.getChildAt(i);
                RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
                int position = params.getViewAdapterPosition();
                String indexName = mData.get(position).getFirstChar();
                if (indexName == null) { 
                    continue;
                }
                if (position > 0 && !TextUtils.equals(indexName, mData.get(position - 1).getFirstChar())) { 
                    // 背景
                    int top = child.getTop() - params.topMargin - mDecorationHeight;
                    int bottom = top + mDecorationHeight;
                    c.drawRect(left, top, right, bottom, mBgPaint);
                    // 文字
                    mTextPaint.getTextBounds(indexName, 0, indexName.length(), mTextBounds);
                    int h = mTextBounds.height();
                    c.drawText(indexName, left + textMarginLeft, bottom - (mDecorationHeight - h) / 2.0f, mTextPaint);
                }
            }
        }
    
        @Override
        public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) { 
            super.onDrawOver(c, parent, state);
    
            int firstVisibleItemPosition = ((LinearLayoutManager) parent.getLayoutManager()).findFirstVisibleItemPosition();
            // 第一个也不展示decoration
            if (firstVisibleItemPosition <= 0) { 
                return;
            }
    
            boolean hasTrans = false;
            String indexName = mData.get(firstVisibleItemPosition).getFirstChar();
            // 移动decoration
            if (firstVisibleItemPosition + 1 < mData.size()) { 
                String nextIndexName = mData.get(firstVisibleItemPosition + 1).getFirstChar();
                if (!TextUtils.equals(indexName, nextIndexName)) { 
                    View firstVisibleChild = parent.getChildAt(0);
                    int transY = firstVisibleChild.getBottom() - (parent.getPaddingTop() + mDecorationHeight);
                    if (transY < 0) { 
                        c.save();
                        c.translate(0, transY);
                        hasTrans = true;
                    }
                }
            }
            float left = parent.getLeft();
            float top = parent.getPaddingTop();
            float right = parent.getWidth() - parent.getPaddingRight();
            float bottom = top + mDecorationHeight;
            // 背景
            c.drawRect(left, top, right, bottom, mBgPaint);
            mTextPaint.getTextBounds(indexName, 0, indexName.length(), mTextBounds);
            //文字
            float baseline = bottom - (mDecorationHeight - mTextBounds.height()) / 2.0f;
            c.drawText(indexName, parent.getPaddingLeft() + textMarginLeft, baseline, mTextPaint);
            if (hasTrans) { 
                c.restore();
            }
        }
    }

参考文献：https://www.jianshu.com/p/3221b5c8fc38

[20210520202246305.gif_pic_center]: /images/20221020/8c4d5a0820b24b4cb6e2aa0f102fe9d1.png