Android的recyclerView findViewHolderForAdapterPosition返回null [英] Android recyclerView findViewHolderForAdapterPosition returns null

问题描述

我想点击一个recyclerView编程的项目，我发现<一个href=\"http://stackoverflow.com/questions/29745919/clicking-on-item-programmatically-in-recyclerview\">a 方式做到这一点：

I want to click a item in recyclerView programmatically, I found a way do that:

recyclerView.findViewHolderForAdapterPosition(0).itemView.performClick();

但它不为我工作，findViewHolderForAdapterPosition刚刚返回null。

but it doesn't work for me, the findViewHolderForAdapterPosition just returns null.

我错过了什么在我的code？

Did I miss something in my code?

HistoryListAdapter：

HistoryListAdapter:

public class HistoryListAdapter extends RecyclerView.Adapter<HistoryListAdapter.ViewHolder> {
private static ArrayList<RecordItem> recordItems;
private static FragmentActivity activity;
private static RecordList recordList;

public HistoryListAdapter(ArrayList<RecordItem> recordItems, FragmentActivity FA, RecordList FRL) {
    this.recordItems = recordItems;
    this.activity = FA;
    this.recordList = FRL;
}

@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    // create a new view
    View itemLayoutView = LayoutInflater.from(parent.getContext()).inflate(R.layout.recorditem, parent, false);
    return new ViewHolder(itemLayoutView);
}

@Override
public void onBindViewHolder(final ViewHolder viewHolder, final int position) {
    // TextView setText ...
}

// Return the size of the itemsData (invoked by the layout manager)
@Override
public int getItemCount() {
    return recordItems.size();
}

// inner class to hold a reference to each item of RecyclerView
public static class ViewHolder extends RecyclerView.ViewHolder{
    public TextView result, datetime;

    public ViewHolder(View itemLayoutView) {
        super(itemLayoutView);
        itemLayoutView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (activity != null) {
                    // do something...
                }
            }
        });
        result = (TextView) itemLayoutView.findViewById(R.id.result);
        heartrate = (TextView) itemLayoutView.findViewById(R.id.heartrate);
        datetime = (TextView) itemLayoutView.findViewById(R.id.datetime);
    }
}
}

RecordList：

RecordList:

RecyclerView listView = (RecyclerView) layoutView.findViewById(R.id.listView);
HistoryListAdapter listadapter = new HistoryListAdapter(itemsToShow, getActivity(), RecordList.this);
listView.swapAdapter(listadapter, false);
listView.findViewHolderForAdapterPosition(0).itemView.performClick();

我省略了一些code，但它不应该影响我的code的整体结构。

I omitted some code, But it should not affect the overall structure of my code.

推荐答案

按照<一个href=\"https://developer.android.com/intl/zh-cn/reference/android/support/v7/widget/RecyclerView.html#findViewHolderForAdapterPosition(int)\"相对=nofollow>官方文档：

如果notifyDataSetChanged（）被调用，但新的布局有不
  经过计算尚未，此方法将返回的无效由于新
  直到布局计算的景色的位置是未知的。

if notifyDataSetChanged() has been called but the new layout has not been calculated yet, this method will return null since the new positions of views are unknown until the layout is calculated.

这不是安全使用 findViewHolderForAdapterPosition（）。

当你调用后 listView.swapAdapter（listadapter，FALSE）此方法; 您总能获得一个空作为的结果，因为 notifyDataSetChanged（）将被调用。

While you call this method after listView.swapAdapter(listadapter, false); you'll always get a null as result because notifyDataSetChanged() will be called.

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