问题描述： 在使用RecyclerView实现水平滚动的布局时，如果使用GridLayoutManager并添加了ItemDecoration，则会发现装饰物会错位或缺失。这是由于GridLayoutManager的实现中，对于装饰物的绘制并没有进行完备的处理。

解决步骤： 我们可以通过重写GridLayoutManager的onDraw方法，手动绘制装饰物来解决此问题，代码示例如下：

private final Rect mBounds = new Rect(); //用于存储当前item的位置信息 @Override public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) { final int childCount = parent.getChildCount(); final int spanCount = getSpanCount(); for (int i = 0; i < childCount; i++) { final View child = parent.getChildAt(i); final int position = parent.getChildAdapterPosition(child); if (position < spanCount) { continue; } /** 绘制顶部装饰物 / if (position % spanCount == 0) { mBounds.set(parent.getPaddingLeft(), parent.getPaddingTop(), parent.getWidth() - parent.getPaddingRight(), child.getTop()); drawTop(c, parent, mBounds); } /* 绘制底部装饰物 / drawBottom(c, parent, child, spanCount); /* 绘制item右边装饰物 */ if ((position + 1) % spanCount != 0) { mBounds.set(child.getRight(), child.getTop(), child.getRight() + getDecorationWidth(), child.getBottom()); drawRight(c, parent, mBounds); } } } private void drawTop(Canvas c, RecyclerView parent, Rect bounds) { final Drawable drawable = getTopDecoration(); drawable.setBounds(bounds); drawable.draw(c); } private void drawBottom(Canvas c, RecyclerView parent, View child, int spanCount) { final RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) child.getLayoutParams(); final int position = parent.getChildAdapterPosition(child); final Drawable drawable = getBottomDecoration(); if (position >= spanCount) { mBounds.set(child.getLeft() - layoutParams.leftMargin, child.getTop() - getDecorationWidth(), child.getRight(), child.getTop()); drawable.setBounds(mBounds); drawable.draw(c); } } private void drawRight(Canvas c, RecyclerView parent, Rect bounds) { final Drawable drawable = getRightDecoration(); drawable.setBounds(bounds); drawable.draw(c); }

在此代码中，我们重载了onDraw