android - 如何选择性地装饰 RecyclerView 项目

Question

我正在根据这个要点创建 ItemDecoration 的子类:https://gist.github.com/alexfu/0f464fc3742f134ccd1e

如何让它只装饰有一定条件的元素？例如，只装饰具有特定位置、ViewHolder 类型等的项目。

我已使用此代码修改了上述要点(以及对已弃用的 Android API 的一些更改)，但 所有项目 无论如何都会得到修饰:

public boolean isDecorated(View view, RecyclerView parent) {
    RecyclerView.ViewHolder holder = parent.getChildViewHolder(view);
    return holder instanceof MenuIconViewHolder || holder instanceof MenuDetailViewHolder;
}

@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
    if (isDecorated(view, parent)) {
        if (mOrientation == VERTICAL_LIST) {
            outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
        } else {
            outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
        }
    } else {
        super.getItemOffsets(outRect, view, parent, state);
    }
}

上面的代码有什么问题？ 顺便说一句，将这种代码放在 ItemDecoration 类中是否被认为是最佳实践(关于关注点分离)？

Answer 1

您还需要在 draw 方法上调用 isDecorated，因为此时您没有在这些项目上放置偏移量，但您仍然在上面绘制。

该方法循环遍历当前在屏幕上可见的 RecyclerView 中的所有 subview 。

public void drawVertical(Canvas c, RecyclerView parent) {
    final int left = parent.getPaddingLeft();
    final int right = parent.getWidth() - parent.getPaddingRight();

    final int childCount = parent.getChildCount();
    for (int i = 0; i < childCount; i++) {
        final View child = parent.getChildAt(i);
        if(isDecorated(child, parent))
        {
            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                .getLayoutParams();
            final int top = child.getBottom() + params.bottomMargin;
            final int bottom = top + mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }
}

public void drawHorizontal(Canvas c, RecyclerView parent) {
    final int top = parent.getPaddingTop();
    final int bottom = parent.getHeight() - parent.getPaddingBottom();

    final int childCount = parent.getChildCount();
    for (int i = 0; i < childCount; i++) {
        final View child = parent.getChildAt(i);
        if(isDecorated(child, parent))
        {
            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                .getLayoutParams();
            final int left = child.getRight() + params.rightMargin;
            final int right = left + mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }
}