【达内课程】SQLite（四）项目之删除联系人列表

【达内课程】OptionsMenu

【达内课程】ContextMenu

看这节之前先学习以上两节

我们先做出如下效果

MainActivity

public class MainActivity extends AppCompatActivity implements View.OnClickListener,DialogInterface.OnClickListener{
    ......

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ......

        //为listview注册ContextMenu
        registerForContextMenu(lv_contacts);
    }

    public static final int MENU_ITEM_EDIT = 1;
    public static final int MENU_ITEM_DELETE = 2;
    @Override
    public void onCreateContextMenu(ContextMenu menu,
                                     View v,
                                     ContextMenu.ContextMenuInfo menuInfo) {
        //将参数转换为AdapterView.AdapterContextMenuInfo类型
        AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) menuInfo;
        int pos = info.position;
        Person p = persons.get(pos);
        menu.add(Menu.NONE,MENU_ITEM_EDIT,Menu.NONE,"编辑"+p.getName()+"的个人信息");
        menu.add(Menu.NONE,MENU_ITEM_DELETE,Menu.NONE,"删除"+p.getName()+"的个人信息");
        super.onCreateContextMenu(menu, v, menuInfo);
    }

    @Override
    public boolean onContextItemSelected(MenuItem item) {
        switch (item.getItemId()){
            case MENU_ITEM_EDIT:
                break;
            case MENU_ITEM_DELETE:
                //弹出确认对话框
                AlertDialog.Builder builder = new AlertDialog.Builder(this);
                AlertDialog dialog = builder.setTitle("警告")
                                            .setMessage("删除操作不可恢复，确定删除吗？")
                                            .setPositiveButton("确定",this)
                                            .setNegativeButton("取消",null)
                                            .create();
                dialog.show();
                break;
        }
        return super.onContextItemSelected(item);
    }

    ......

    @Override
    public void onClick(DialogInterface dialogInterface, int i) {
        //删除

    }
}

然后我们增加删除功能

IDao

public interface IDao<T> {
    long insert(T t);

    List<T> query(String whereClause,String[] whereArgs,String orderBy);

    int delete(int id);
}

PersonDao中重写delete方法，暂时先不实现

 @Override
    public int delete(int id) {
        return 0;
    }

MainActivity中我们要把操作的position作为全局变量记录下来

    private int actionPosition;
   private int actionPosition;
    @Override
    public void onCreateContextMenu(ContextMenu menu,
                                     View v,
                                     ContextMenu.ContextMenuInfo menuInfo) {
        //将参数转换为AdapterView.AdapterContextMenuInfo类型
        AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) menuInfo;
        actionPosition = info.position;
        menu.add(Menu.NONE,MENU_ITEM_EDIT,Menu.NONE,"编辑"+persons.get(actionPosition).getName()+"的个人信息");
        menu.add(Menu.NONE,MENU_ITEM_DELETE,Menu.NONE,"删除"+persons.get(actionPosition).getName()+"的个人信息");
        super.onCreateContextMenu(menu, v, menuInfo);
    }

然后增加点击删除的事件

@Override
    public void onClick(DialogInterface dialogInterface, int i) {
        //删除
        PersonDao personDao = new PersonDao(this);
        int affectedRows = personDao.delete(persons.get(actionPosition).getId());
        if(affectedRows > 0){
            Toast.makeText(this,"删除成功",Toast.LENGTH_SHORT).show();
            //获取新数据,刷新页面
            persons.clear();
            persons.addAll(personDao.query(null, null, "_name ASC"));
            adapter.notifyDataSetChanged();
        }else {
            Toast.makeText(this,"删除失败，请联系管理员",Toast.LENGTH_SHORT).show();
        }
    }

现在我们来重点看下PersonDao中的delete方法如何实现

@Override
    public int delete(int id) {
        //获取SQLiteDatabase对象
        DBOpenHelper dbOpenHelper = new DBOpenHelper(context);
        SQLiteDatabase db = dbOpenHelper.getWritableDatabase();
        //执行业务：删除数据
        String table = "users";
        String whereClause = "_id = ?";
        String[] whereArgs = {id+""};
        int affectedRoew = db.delete(table,whereClause,whereArgs);
        //释放资源
        db.close();
        db = null;
        //返回
        return affectedRoew;
    }

效果图