首先显示在项目后面绘制RecyclerView ItemDecoration

Question

我只需要将itemDecoration添加到一个项目中。它起作用，但首先显示装饰没有自己的空间。但是当我开始滚动时，它将获得自己的空间。以下是我从here

部分获取的代码

View spacer;

    public NewMessageHeaderDecoration() {
        spacer = null; 
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDraw(c, parent, state);

        if (spacer == null) { // If layout is not already inflated
            spacer = LayoutInflater.from(parent.getContext()).inflate(R.layout.view_holder_new_messages_header, parent, false);
            fixLayoutSize(spacer, parent);
        }

        // go through all the recycler views parents
        for (int i = 0; i < parent.getChildCount(); i++) {
            View child = parent.getChildAt(i);
            int pos = parent.getChildAdapterPosition(child);
            long msgSerial = ((ChatAdapter)parent.getAdapter()).getItemSerial(pos);

            if(msgSerial == 40) {

                c.save(); 
                c.translate(0, child.getTop() - 2 - spacer.getHeight());
                spacer.draw(c);
                c.restore(); 
            } 
        }
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);

        int position = parent.getChildAdapterPosition(view);
        if (position == RecyclerView.NO_POSITION || position == 0 || spacer == null) {
            return;
        }

        outRect.top = 2 + spacer.getHeight(); 
    }

    protected void fixLayoutSize(View view, ViewGroup parent) {
        if (view.getLayoutParams() == null) {
            view.setLayoutParams(new ViewGroup.LayoutParams(
                    ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT));
        }

        int widthSpec = View.MeasureSpec.makeMeasureSpec(parent.getWidth(), View.MeasureSpec.EXACTLY);
        int heightSpec = View.MeasureSpec.makeMeasureSpec(parent.getHeight(), View.MeasureSpec.UNSPECIFIED);

        int childWidth = ViewGroup.getChildMeasureSpec(widthSpec,
                parent.getPaddingLeft() + parent.getPaddingRight(), view.getLayoutParams().width);
        int childHeight = ViewGroup.getChildMeasureSpec(heightSpec,
                parent.getPaddingTop() + parent.getPaddingBottom(), view.getLayoutParams().height);

        view.measure(childWidth, childHeight);

        view.layout(0, 0, view.getMeasuredWidth(), view.getMeasuredHeight());
    }