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

问题描述

我想以编程方式点击 recyclerView 中的一个项目，我找到了一种方法 这样做:

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

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

但它对我不起作用，findViewHolderForAdapterPosition 只返回 null.

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

我是否遗漏了代码中的某些内容?

Did I miss something in my code?

历史列表适配器:

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);
    }
}
}

记录列表:

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();

我省略了一些代码，但应该不会影响我代码的整体结构.

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

推荐答案

根据官方文档:

如果notifyDataSetChanged()已被调用但新布局没有尚未计算，此方法将返回null，因为新的在计算布局之前，视图的位置是未知的.

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.

使用 findViewHolderForAdapterPosition() 是不安全的.

当你在 listView.swapAdapter(listadapter, false); 之后调用这个方法时，你总是会得到一个 null 作为结果，因为 notifyDataSetChanged()code> 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.

这篇关于Android recyclerView findViewHolderForAdapterPosition 返回 null的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！