android使用ItemDecoration给RecyclerView 添加水印

public class MyDrawable extends Drawable { Paint mPaint; public MyDrawable() {  mPaint = new Paint();  mPaint.setColor(Color.parseColor("#1A000000"));  mPaint.setAntiAlias(true);  mPaint.setTextAlign(Paint.Align.LEFT);//从字的最左边开始画  mPaint.setTextSize(54); } @Override public void draw(@NonNull Canvas canvas) {  Rect r = getBounds();  //画斜着的字  canvas.save();  canvas.rotate(-30, r.left, r.bottom);  canvas.drawText("哈哈哈哈哈哈哈", r.left, r.bottom, mPaint);  canvas.restore(); } /*  复写这两个方法是为了当在控件wrap_content时能自己测量出高，同时也方便布局。 */  //倾斜30度，可以算出高来 @Override public int getIntrinsicHeight() {  return (int) (Math.sqrt(3) / 3 * getIntrinsicWidth() + 0.5F); } @Override public int getIntrinsicWidth() {  return (int) (mPaint.measureText("DecorationDraw") + 0.5F); } //...模板方法省略}

public class MyDecoration extends RecyclerView.ItemDecoration { private Drawable mDivider; private int mScrollY; public MyDecoration() {  mDivider = new MyDrawable(); } @Override public void onDraw(Canvas canvas, RecyclerView parent, RecyclerView.State state) {  //清除之前画的  // canvas.drawColor(Color.WHITE);  /*   * 跟着滑动是因为bounds在不停的变化，就是top   */  int top = UIUtil.dp(20) - mScrollY;  // 对于画多少个水印，根据业务需求来，这里直接画count个  int itemCount = parent.getAdapter().getItemCount();  // 进行布局  for (int i = 0; i < itemCount; ++i) {   int left = i % 2 == 0 ? UIUtil.dp(20) : parent.getMeasuredWidth() -mDivider.getIntrinsicWidth() - UIUtil.dp(20);   //通过setBounds来控制水印的左右   mDivider.setBounds(left, top, parent.getMeasuredWidth(), top + mDivider.getIntrinsicHeight());   mDivider.draw(canvas);   if (i % 2 == 0) {    top += UIUtil.dp(20) + mDivider.getIntrinsicHeight();   } else {    top += UIUtil.dp(140) + mDivider.getIntrinsicHeight();   }  } } /*  mScrollY用于监测recyclerView的滑动距离，此处使用的是onScrollListener中dy的累加值，当item不发生删除添加操作时是准确的 */  public void setScrollY(int scrollY) {  this.mScrollY = scrollY; }}

private int totallyY = 0;recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() { @Override public void onScrolled(RecyclerView recyclerView, int dx, int dy) {  totallyY += dy;  myDecoration.setScrollY(totallyY);  }});