Question

我正在尝试在我的Recyclerview Adapter和Activity之间创建一个接口，这样当单击适配器中的某个项时，Activity会相应地做出反应，但是监听器始终为null。

接口

public interface UrlTagCatClickedListener {
    public void onUrlTagCatClicked (String chemicalURL);
}

适配器

public class TagCatAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    private Context mContext;
    private List<TagCatItem> mTagCatItems;
    private int lastPosition = -1;

    private UrlTagCatClickedListener mTagCatClickedListener;

    public  TagCatAdapter(List<TagCatItem> tagCatItems, Context context) {
        super();
        this.mTagCatItems = tagCatItems;
        this.mContext = context;
        this.mTagCatClickedListener = null;
    }

    public void setTagCatClickedListener (UrlTagCatClickedListener tagCatClickedListener) {
        this.mTagCatClickedListener = tagCatClickedListener;
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View v = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.tag_cat_item, parent, false);
        return new ItemViewHolder(v);
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        final  TagCatItem tagCatItem = mTagCatItems.get(position);
        ((ItemViewHolder) holder).chemicalTitle.setText(Html.fromHtml(tagCatItem.getChemicalTitle()));
        ((ItemViewHolder) holder).chemicalDate.setText(tagCatItem.getChemicalDate());
        ((ItemViewHolder) holder).chemicalTitle.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (mTagCatClickedListener != null) { // mTagCatClickedListener is always null
                    mTagCatClickedListener.onUrlTagCatClicked(tagCatItem.getChemicalURL());
                }
            }
        });
    }

    public  class  ItemViewHolder extends RecyclerView.ViewHolder{
        public TextView chemicalTitle, chemicalDate;
        public  ItemViewHolder(final View mView) {
            super(mView);
            chemicalTitle = (TextView) mView.findViewById(R.id.tagcat_title);
            chemicalDate = (TextView) mView.findViewById(R.id.tagcat_date);
        }
    }



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

活动

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d(TAG, "onCreate called")
        //Skipped a lot of codes that doesn't relate to the queation

        List<TagCatItem> mTagCatItems = new ArrayList<>();

        TagCatAdapter tagCatAdapter = new TagCatAdapter(mTagCatItems, this);
        tagCatAdapter.setTagCatClickedListener(new UrlTagCatClickedListener() {
            @Override
            public void onUrlTagCatClicked(String chemicalURL) {
                Log.d(TAG, "I go the url!!!!!!!!!! and it is + " + chemicalURL);
            }
        });
    }

请你知道为什么它为空以及如何修复它？

Answer 1

您在给定的设置中有两个不同的TagCatAdapter实例;一个位于Activity，一个位于Fragment。您已经在UrlTagCatClickedListener创建的Activity上设置了Fragment，但它是TagCatAdapter＆＃39; s {{1}您在RecyclerView上设置的实例。那个人没有设置监听器，所以它的mTagCatClickedListener总是为空。

您只需将给定的UrlTagCatClickedListener移至TagCatAdapter中的Fragment，然后移除TagCatAdapter中的Activity，就像您一样。 ;无论如何都不要使用那个。

为什么这个自定义侦听器为null？

1 个答案: