棉绒错误“不要将位置视为固定；只能立即使用..." [英] Lint error "Do not treat position as fixed; only use immediately..."

问题描述

我正在为开源库做贡献，并且出现了lint错误不要将位置视为固定；只能立即使用，并调用holder.getAdapterPosition()稍后再查找" :

I'm contributing to open source library and got lint error "Do not treat position as fixed; only use immediately and call holder.getAdapterPosition() to look it up later" for this code:

  @Override public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
    mAdapter.onBindViewHolder(holder, position);

    if (!isFirstOnly || position > mLastPosition) {
      for (Animator anim : getAnimators(holder.itemView)) {
        anim.setDuration(mDuration).start();
        anim.setInterpolator(mInterpolator);
      }
      mLastPosition = position;
    } else {
      ViewHelper.clear(holder.itemView);
    }
  }

我检查过，是因为该位置已保存以备将来使用.对于图书馆创建者来说，这是一个问题，为什么他们需要这种逻辑.但是，当我将职位的用法更改为用法holder.getAdapterPosition()时，问题消失了:

I've checked that it is because the position is saved for the future use. It is a question to library creator why they need this logic. But issue disappeared when I change the usage of the position to the usage holder.getAdapterPosition():

  @Override public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
    mAdapter.onBindViewHolder(holder, position);

    if (!isFirstOnly || holder.getAdapterPosition() > mLastPosition) {
      for (Animator anim : getAnimators(holder.itemView)) {
        anim.setDuration(mDuration).start();
        anim.setInterpolator(mInterpolator);
      }
      mLastPosition = holder.getAdapterPosition();
    } else {
      ViewHelper.clear(holder.itemView);
    }
  }

我认为从概念上讲它变化不大，但现在皮棉很满意.为什么?

I assume that conceptually it didn't change much but lint is satisfied now. Why?

推荐答案

请注意，与ListView不同，RecyclerView不会调用此方法 如果项目的位置在数据集中发生了变化，则再次 项目本身无效或无法确定新位置. 因此，您只能在 在此方法内获取相关数据项，因此不应保留 它的副本.如果以后需要某个物品的位置(例如 单击侦听器)，使用getAdapterPosition()将具有更新的 适配器位置

Note that unlike ListView, RecyclerView will not call this method again if the position of the item changes in the data set unless the item itself is invalidated or the new position cannot be determined. For this reason, you should only use the position parameter while acquiring the related data item inside this method and should not keep a copy of it. If you need the position of an item later on (e.g. in a click listener), use getAdapterPosition() which will have the updated adapter position

因此，从技术上讲，项目可能会重新排列(例如排序或移动)，并且由于项目尚未失效，因此不需要绑定.这意味着如果项目显示相同的数据，而仅更改列表中的位置/索引，则可能不会调用onBindViewHolder().接收到的position变量仅在bind函数的范围内成立，并不总是指向数据集中的正确位置.这就是为什么每次需要更新位置时都必须调用函数getAdapterPosition()的原因.

So, technically items may be re-arranged (like sorted, or moved around) and binding will not be necessary because items are not invalidated yet. This means onBindViewHolder() may NOT be called if items show the same data, but just their position/index in a list changes. The position variable received holds true only for the scope of bind function and will not always point to the correct position in the data set. That's why the function getAdapterPosition() must be called every time updated position is needed.

恕我直言，mLastPosition = holder.getAdapterPosition();仍然可能是错误的.因为可能会重新排列项目，并且mLastPosition仍指向旧位置.

IMHO, mLastPosition = holder.getAdapterPosition(); is still potentially wrong. Because item may be re-arranged and mLastPosition still points to old position.

关于皮棉为何保持沉默的原因，也许皮特的规则并不那么彻底.只是检查是否正在复制position参数.

About why lint is silent, perhaps Lint's rule is not that thorough. It's only checking whether the position parameter is being copied or not.

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