对于屏幕外项目,RecyclerView findViewHolder为null

Question

[第一次提问者和第一次安卓编码器所以我道歉,如果我做错了什么]

我正在尝试更改我的回收器上的itemview内部的值.但是,如果该项目视图恰好在屏幕外,则findViewBy [布局,适配器或ID]将显示为null.

public void setUserActive(UserListAdapter adapter, RecyclerView recyclerView, int position, View v) {recyclerView.findViewHolderForItemId(adapter.getItemId(position));
    TextView txtActive = (TextView) vh.itemView.findViewById(R.id.user_isActive);
    txtActive.setText("Active");
    UserListAdapter.ViewHolder inactivevh = (UserListAdapter.ViewHolder) recyclerView.findViewHolderForItemId(adapter.getItemId(adapter.getActiveUserPosition()));
    TextView txtInActive = (TextView) inactivevh.itemView.findViewById(R.id.user_isActive);
    txtInActive.setText("");
    adapter.setActiveUserPosition(position);
}

我尝试了几种不同的方法,从使用

  UserListAdapter.ViewHolder vh = (UserListAdapter.ViewHolder) recyclerView.findViewHolderForLayoutPosition(position);

要么

UserListAdapter.ViewHolder inactivevh = (UserListAdapter.ViewHolder) recyclerView.findViewHolderForAdapterPosition(position)

当应该处于inactivevh的视图关闭时,它们都会失败.

我已将适配器设置为hasStableIDs = true notifydatasetchanged似乎也没有帮助.

Answer 1

如果某个项目在屏幕上(布局),您可以使用您描述的方法方便地获取其视图持有者.如果一个项目不在屏幕上,它将在通过滚动后立即更新onBindViewHolder.如果没有滚动,则不会向用户显示任何更新它的尝试是浪费处理能力(除了因为项目没有分配视图持有者而无法实现).

含义:以onBindViewHolder能够提取最新数据的方式实现适配器.看起来你已经全部设置好了,可以使用这个:

public void setUserActive(UserListAdapter adapter, RecyclerView recyclerView, int position) {
    // Retrieve the old active user ID so we can mark him deactivated.
    final int oldUserActivePosition = adapter.getActiveUserPosition();

    // Setup the adapter with current data.
    adapter.setActiveUserPosition(position);

    // Do NOT use stable IDs and this method. It just doesn't work as expected.
    // recyclerView.findViewHolderForItemId(adapter.getItemId(position));

    // Activate new user.
    UserListAdapter.ViewHolder holder = (UserListAdapter.ViewHolder) recyclerView.findViewHolderForAdapterPosition(position);
    if (holder == null) {
        // The item is off screen, no need to update it yet.
    } else {
        // Update the on screen item. The logic is already implemented in the adapter.
        adapter.onBindViewHolder(holder, position);
    }

    // Deactivate previous user.
    holder = (UserListAdapter.ViewHolder) recyclerView.findViewHolderForAdapterPosition(oldUserActivePosition);
    if (holder != null) {
        adapter.onBindViewHolder(holder, oldUserActivePosition);
    }
}

当然,简化代码中的if-else块.

编辑:

我刚刚意识到原始解决方案是多么复杂.只要适配器可以对您需要的所有事件做出反应,onBindViewHolder并且绑定非常简单,这就足够了:

public void setActiveUserPosition(int position) {
    if (mActiveUserPosition != position) {
        int oldPosition = mActiveUserPosition;
        mActiveUserPosition = position;
        notifyItemChanged(oldPosition);
        notifyItemChanged(position);
    }
}

您现在需要调用的只是adapter.setActiveUserPosition(position);渲染setUserActive方法已过时.