Java 如果在数组字符串上，则RecyclerView数组为null

我正在研究Android回收视图，我发现了这个例子

回收适配器

public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.ViewHolder> {
    private String[] titles = {"Capter One",
    "Chapter Two",
            "Chapter Three",
            "Chapter Four",
            "Chapter Five",
            "Chapter Six"
    };
    private  String[] details = {"Det..One","Det..Two","Det.. Three","Det...Four","Det.. Five","Det..Six"};

    private int[] images = {R.drawable.android_image_1,
            R.drawable.android_image_2,
            R.drawable.android_image_3,
            R.drawable.android_image_4,
            R.drawable.android_image_5,
            R.drawable.android_image_6
    };
@Override
public ViewHolder onCreateViewHolder( ViewGroup viewGroup, int i ){
    View v = LayoutInflater.from (viewGroup.getContext ()).inflate (R.layout.card_layout, viewGroup,false);
    ViewHolder viewHolder = new ViewHolder (v);
    return viewHolder;

}

    @Override
    public void onBindViewHolder(ViewHolder viewHolder, int i) {
        viewHolder.itemTitle.setText(titles[i]);
        viewHolder.itemDetail.setText(details[i]);
        viewHolder.itemImage.setImageResource(images[i]);
    }
    @Override
    public int getItemCount() {
        return titles.length;
    }

    class ViewHolder extends RecyclerView.ViewHolder /*implements Inter*/{
        ImageView itemImage;
        TextView itemTitle;
        TextView itemDetail;

        ViewHolder( View itemView ){
            super(itemView);
            itemImage = itemView.findViewById (R.id.item_image);
            itemTitle = itemView.findViewById (R.id.item_title);
            itemDetail = itemView.findViewById (R.id.item_detail);
            itemView.setOnClickListener (new View.OnClickListener () {
                @Override
                public void onClick ( View v ) {
                    int position = getAdapterPosition ();
                    position +=1;
                    Snackbar.make (v,"click on position" + titles[position],Snackbar.LENGTH_SHORT).setAction ("Action", null).show ();


                }
            });
            }
    }
}

没什么特别的，而且效果很好。 我只是做了一点“最佳实践”的改变我想从资源文件中获取标题数组，如下所示：

<resources>
    <string-array name="titles">
        <item>Chap 1</item>
        <item>Chap 2</item>
        <item>Chap 3</item>
        <item>Chap 4</item>
        <item>Chap 5</item>
        <item>Chap 6</item>
        <item>Chap 7</item>
        <item>Chap 8</item>
    </string-array>

</resources>

但当我运行应用程序时，我得到java.lang.NullPointerException：尝试获取空数组的长度 在com.example.evenbook.RecyclerAdapter.getItemCount（RecyclerAdapter.java:55）上

数组在中为空

public int getItemCount() {
        return titles.length;
    }

如果我尝试使用return 5，就可以了（它只显示5个卡片项目）

我还认为getItemCount方法是在onCreateViewHolder之前启动的，但我认为这是不可能的。 发生了什么？ 提前感谢

尝试以下更改：

public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.ViewHolder> {
    private String[] titles;
    private  String[] details;
    private int[] images;

    public RecyclerAdapter() {
        this.titles =  = {"Capter One",
            "Chapter Two",
            "Chapter Three",
            "Chapter Four",
            "Chapter Five",
            "Chapter Six"
        };
        this.details =  = {"Det..One","Det..Two","Det.. Three","Det...Four","Det.. Five","Det..Six"};
        this.images =  = {R.drawable.android_image_1,
            R.drawable.android_image_2,
            R.drawable.android_image_3,
            R.drawable.android_image_4,
            R.drawable.android_image_5,
            R.drawable.android_image_6
        };
    }

    @Override
    public ViewHolder onCreateViewHolder( ViewGroup viewGroup, int i ){
        View v = LayoutInflater.from (viewGroup.getContext ()).inflate (R.layout.card_layout, viewGroup,false);
        ViewHolder viewHolder = new ViewHolder (v);
        return viewHolder;

    }

    @Override
    public void onBindViewHolder(ViewHolder viewHolder, int i) {
        viewHolder.itemTitle.setText(titles[i]);
        viewHolder.itemDetail.setText(details[i]);
        viewHolder.itemImage.setImageResource(images[i]);
    }
    @Override
    public int getItemCount() {
        return titles.length;
    }

    class ViewHolder extends RecyclerView.ViewHolder /*implements Inter*/{
        ImageView itemImage;
        TextView itemTitle;
        TextView itemDetail;

        ViewHolder( View itemView ){
            super(itemView);
            itemImage = itemView.findViewById (R.id.item_image);
            itemTitle = itemView.findViewById (R.id.item_title);
            itemDetail = itemView.findViewById (R.id.item_detail);
            itemView.setOnClickListener (new View.OnClickListener () {
                @Override
                public void onClick ( View v ) {
                    int position = getAdapterPosition ();
                    position +=1;
                    Snackbar.make (v,"click on position" + titles[position],Snackbar.LENGTH_SHORT).setAction ("Action", null).show ();


                }
            });
        }
    }
}

公共类RecyclerAdapter扩展了RecyclerView.Adapter{ 私有字符串[]标题； 私有字符串[]详细信息； 私有int[]图像； 公共回收设备适配器（）{ this.titles=={“捕获者一号”， “第二章”， “第三章”， “第四章”， “第五章”， “第六章” }; 这个.细节={“一号”、“二号”、“三号”、“四号”、“五号”、“六号”}； this.images=={R.drawable.android_image_1， R.drawable.android_image_2， R.drawable.android_image_3， R.drawable.android_image_4， R.drawable.android_image_5， R.drawable.android_image_6 }; } @凌驾 公共视图持有者onCreateViewHolder（视图组视图组，int i）{ 视图v=LayoutInflater.from（viewGroup.getContext（））.flate（R.layout.card\u布局，viewGroup，false）； 视窗夹持器视窗夹持器=新视窗夹持器（v）； 返回视图持有者； } @凌驾 公共无效onBindViewHolder（ViewHolder ViewHolder，int i）{ viewHolder.itemTitle.setText（titles[i]）； viewHolder.itemdail.setText（细节[i]）； viewHolder.itemImage.setImageResource（images[i]）； } @凌驾 public int getItemCount（）{ 返回标题。长度； } 类ViewHolder扩展了RecyclerView.ViewHolder/*实现了*/{ 图像查看项目图像； 文本视图项目标题； 文本视图项目详细信息； ViewHolder（视图项视图）{ 超级（项目视图）； itemImage=itemView.findViewById（R.id.item\u图像）； itemTitle=itemView.findViewById（R.id.item\u title）； itemDetail=itemView.findViewById（R.id.item\u详细信息）； itemView.setOnClickListener（新的View.OnClickListener（）{ @凌驾 公共void onClick（视图v）{ int position=getAdapterPosition（）； 位置+=1； Snackbar.make（v，“点击位置”+标题[position]，Snackbar.LENGTH\u SHORT）.setAction（“Action”，null）.show（）； } }); } } }

---

您可以使用

getResources（）.getStringArray

    String[] array = getResources().getStringArray(R.array.titles);

然后可以更改适配器构造函数以接受字符串数组

String[]

    RecyclerAdapter adapter = new RecyclerAdapter(array);

公共类RecyclerAdapter扩展了RecyclerView.Adapter{ 私有字符串[]标题； RecyclerAdapter（字符串[]标题）{ this.titles=标题； } //…其他同学 }

---

有效，谢谢！！如果我想在RecycleAdapter类中获取数组，怎么可能？

public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.ViewHolder> {
    private String[] titles;
    private  String[] details;
    private int[] images;

    public RecyclerAdapter() {
        this.titles =  = {"Capter One",
            "Chapter Two",
            "Chapter Three",
            "Chapter Four",
            "Chapter Five",
            "Chapter Six"
        };
        this.details =  = {"Det..One","Det..Two","Det.. Three","Det...Four","Det.. Five","Det..Six"};
        this.images =  = {R.drawable.android_image_1,
            R.drawable.android_image_2,
            R.drawable.android_image_3,
            R.drawable.android_image_4,
            R.drawable.android_image_5,
            R.drawable.android_image_6
        };
    }

    @Override
    public ViewHolder onCreateViewHolder( ViewGroup viewGroup, int i ){
        View v = LayoutInflater.from (viewGroup.getContext ()).inflate (R.layout.card_layout, viewGroup,false);
        ViewHolder viewHolder = new ViewHolder (v);
        return viewHolder;

    }

    @Override
    public void onBindViewHolder(ViewHolder viewHolder, int i) {
        viewHolder.itemTitle.setText(titles[i]);
        viewHolder.itemDetail.setText(details[i]);
        viewHolder.itemImage.setImageResource(images[i]);
    }
    @Override
    public int getItemCount() {
        return titles.length;
    }

    class ViewHolder extends RecyclerView.ViewHolder /*implements Inter*/{
        ImageView itemImage;
        TextView itemTitle;
        TextView itemDetail;

        ViewHolder( View itemView ){
            super(itemView);
            itemImage = itemView.findViewById (R.id.item_image);
            itemTitle = itemView.findViewById (R.id.item_title);
            itemDetail = itemView.findViewById (R.id.item_detail);
            itemView.setOnClickListener (new View.OnClickListener () {
                @Override
                public void onClick ( View v ) {
                    int position = getAdapterPosition ();
                    position +=1;
                    Snackbar.make (v,"click on position" + titles[position],Snackbar.LENGTH_SHORT).setAction ("Action", null).show ();


                }
            });
        }
    }
}

    String[] array = getResources().getStringArray(R.array.titles);

    RecyclerAdapter adapter = new RecyclerAdapter(array);

public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.ViewHolder> {
    private String[] titles;

    RecyclerAdapter(String[] titles) {
        this.titles = titles;
    }

   // ... rest of class
}