android - 如何从自定义 ListView 数组适配器类中的 ListView 中删除行并刷新 ListView 中的剩余项目？

Question

我是 Android 的新手，正在努力提高编程技能。

在这里，我有自定义 ListView 适配器类，我曾在其中显示 ListView 项目，如 TextView 、图像等。

我需要做的是，我在 ListView 中有删除按钮，如果我点击删除按钮， ListView 中的特定行必须被删除，并且需要刷新 ListView 中剩余的行项目。

代码在这里:

public class CustomListViewAdapter1 extends ArrayAdapter<ListView_Model> {
private Activity activity;
List<ListView_Model> books;


public CustomListViewAdapter1(Activity activity, int resource, List<ListView_Model> books) {
    super(activity, resource, books);
    this.activity = activity;

}

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    ViewHolder holder = null;
    LayoutInflater inflater = (LayoutInflater) activity.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
   // If holder not exist then locate all view from UI file.
    if (convertView == null) {
        // inflate UI from XML file
        convertView = inflater.inflate(R.layout.item_listview, parent, false);
        // get all UI view
        holder = new ViewHolder(convertView);
        // set tag for holder
        convertView.setTag(holder);

    } else {
        // if holder created, get tag from view
        holder = (ViewHolder) convertView.getTag();
    }

    ListView_Model book = getItem(position);

    holder.name.setText(book.getName());
    holder.authorName.setText(book.getAuthorName());
    holder.mobileNo.setText(book.getPhNo());
    holder.imgView_lv_delete_btn2= (ImageView) 
    convertView.findViewById(R.id.listview_delete_btn2);
    holder.imgView_lv_delete_btn2.setTag(position);


    holder.imgView_lv_delete_btn2.setOnClickListener(new 
    View.OnClickListener() {
       @Override
       public void onClick(View v) {
//I have commented this line here which is not working

       /*Integer index = (Integer)v.getTag();
           System.out.println("Index is:"+index);

           books.remove(index.intValue());
           notifyDataSetChanged();*/
 }
   });
return convertView;
}

private static class ViewHolder {
    private ImageView images,imgView_lv_edit_btn,imgView_lv_view_btn1,imgView_lv_delete_btn2;

    private TextView name;
    private TextView authorName,mobileNo;

    public ViewHolder(View v) {
        name = (TextView) v.findViewById(R.id.title);
        images = (ImageView) v.findViewById(R.id.thumbnail);
        authorName = (TextView) v.findViewById(R.id.author);
        mobileNo = (TextView) v.findViewById(R.id.MobileNo);

        imgView_lv_edit_btn = (ImageView) v.findViewById(R.id.listview_edit_btn);
        imgView_lv_view_btn1 = (ImageView) v.findViewById(R.id.listview_view_btn1);
     }
}}

我在上面的代码中注释了这一行，因为它不起作用。

          /*Integer index = (Integer)v.getTag();
           System.out.println("Index is:"+index);

           books.remove(index.intValue());
           notifyDataSetChanged();*/

我在这里犯了什么错误，为什么会在这里抛出这个错误？

抛出的错误是:

java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object java.util.List.remove(int)' on a null object reference at CustomListViewAdapter1$1.onClick(CustomListViewAdapter1.java:67)

Answer 1

您没有在 constructor 中分配变量 books。

public CustomListViewAdapter1(Activity activity, int resource, List<ListView_Model> books) {
    super(activity, resource, books);
    this.activity = activity;
    this.books = books; // The missing line
}

现在您的注释代码应该可以工作了!