[单击项时如何通过回调方法将getAdapterPosion（）值传递回调用方Activity

Question

[我试图找到如何将适配器的getAdapterPosion（）结果返回给调用方Activity，但我无法弄清楚。

Adapter类中的回调代码

public class ListAdapter extends RecyclerView.Adapter<ListAdapter.RowViewHolder> {
// Adapter class code
...
    class RowViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
//more code

        public void onClick(View view) {
            if (mClickListener != null) mClickListener.onItemClick(view, getAdapterPosition());
            ListActivity.position = getAdapterPosition();
            final Country currentCountry = countriesList.get(getAdapterPosition());
        }
    }

    public void setClickListener(ItemClickListener itemClickListener) {
        this.mClickListener = itemClickListener;
    }

    public interface ItemClickListener {
        void onItemClick(View view, int position);
    }
...
}

整个适配器类（如果要运行它）

public class ListAdapter extends RecyclerView.Adapter<ListAdapter.RowViewHolder> {

    private ItemClickListener mClickListener;
    FragmentManager fm;
    Activity listActivity;
    private Context context;
    private List<Country> countriesList;

    public ListAdapter(Context context, Activity listActivity) {

        this.fm = fm;
        this.listActivity = listActivity;
        this.context = context;
        countriesList = new ArrayList<>();
    }

    @NotNull
    @Override
    public RowViewHolder onCreateViewHolder(@NotNull ViewGroup parent, int viewType) {

        View itemView = LayoutInflater.from(context)
                .inflate(R.layout.row_list, parent,false);

//        context = parent.getContext();
        return new RowViewHolder(itemView);
    }

    class RowViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

        TextView viewName;
        ImageView viewFlag;

        LinearLayout countryEntry;

        RowViewHolder(View view) {

            super(view);
            viewName = view.findViewById(R.id.name);
            viewFlag = view.findViewById(R.id.flag);
            countryEntry = view.findViewById(R.id.rowId);
            view.setOnClickListener(this);
        }

        @Override
        public void onClick(View view) {
            if (mClickListener != null) mClickListener.onItemClick(view, getAdapterPosition());
            ListActivity.position = getAdapterPosition();
            final Country currentCountry = countriesList.get(getAdapterPosition());
//todo: can i return currentCountry to the listActivity in order to pass it?
        }
    }

    public void setClickListener(ItemClickListener itemClickListener) {
        this.mClickListener = itemClickListener;
    }

    public interface ItemClickListener {
        void onItemClick(View view, int position);
    }

    @Override
    public void onBindViewHolder(@NotNull RowViewHolder holder, int position) {

        final Country currentCountry = countriesList.get(position);
        int id = currentCountry.getId();

        holder.viewName.setText(countriesList.get(position).getName());

        Uri imageUrl = Uri.parse(String.valueOf(countriesList.get(position).getFlag()));

        SvgLoader.pluck()
                .with(listActivity)//Replace new MainActivity with activity
                .setPlaceHolder(R.mipmap.ic_launcher, R.mipmap.ic_launcher)
                .load(imageUrl, holder.viewFlag);

//        holder.viewFlag.setImageURI(Uri.parse(String.valueOf(countriesList.get(position).getFlag())));
//        holder.countryEntry.setOnClickListener(new View.OnClickListener() {
//        });
    }

    @Override
    public int getItemCount() {
        return countriesList.size();
    }

    public void attachCountriesList(List<Country> countriesList) {
        // getting list from Fragment.
        this.countriesList = countriesList;
    }
}

来自活动的呼叫是adapter.setClickListener(this);。我一直在尝试将此调用的结果分配给一个int变量，但它不起作用。

谢谢！

Answer 1

活动不调用适配器。他们实例化它们，然后在RecyclerView上设置适配器。没有什么可退回的。您需要的是对适配器的引用。您可以通过多种方式从活动中获取信息。

设置适配器之前：

ListAdapter adapter = new ListAdapter(parameter, parameter);

recycler.setAdapter(adapter);

获得职位：

int position = adapter.getAdapterPosition();

设置适配器后：

ListAdapter adapter = (ListAdapter)recycler.getAdapter();

使您的代码复杂的事物：

1. 在ListAdapter中，您向构造函数传递Context和ListActivity。 ListActivity已经是一个Context子类，无论何时需要Context，都可以使用ListActivity。

2. 您正在使onClick过程复杂化。您将适配器项设置为clickListeners，然后将活动作为侦听器。当您单击项目时，您将经过2个侦听器（项目本身和listActivity）。您的活动无需成为侦听器（将其称为clickListener不会使其成为一个侦听器，因此它只是一个侦听器）。由于您已经在适配器中引用了您的“活动”，因此您已经可以与其进行通信。因此，不要在onClick中包含以下代码：

public void onClick(View view) {
    if (mClickListener != null) 
      mClickListener.onItemClick(view, getAdapterPosition());
    ListActivity.position = getAdapterPosition();
    final Country currentCountry = countriesList.get(getAdapterPosition());
}

您可能有这个：

public void onClick(View view) {

    listActivity.showItemDetails( view, getAdapterPosition) ;  //you name your method what u want of course, just make sure is public.

    listActivity.setCountries(currentCountries);  //since you have the activity's reference u can pass anything u like including currentCountry

}

然后，您可以摆脱创建的接口以及设置器和获取器。以及其他使该工作奏效的因素。您不需要它！