如何在sqlite android中检索下一个值

Posted 2023-04-19

【中文标题】如何在sqlite android中检索下一个值

【英文标题】：How to retrieve the next value in sqlite android

【发布时间】：2016-01-26 09:41:45

【问题描述】：

您好，我有一个应用程序可以显示学生的姓名和性别。在我的查询中，我将显示限制为 20。如何通过单击下一步按钮应用 21-40 的显示。如果我单击上一个，它也会返回。

MainActivity 类

public class MainActivity extends Activity 

    List<Students> GetAll;
    DatabaseHelper db = new DatabaseHelper(this);
    ListView lv;
    Context context = this;
    DatabaseHelper dbhelper;
    Button btnprevious,btnnext;

    @Override
    protected void onCreate(Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        dbhelper = new DatabaseHelper(MainActivity.this);
        //Add below lines to your original code
        try
            dbhelper.createDataBase();
        
        catch(IOException e)
            e.printStackTrace();
        
        try 
            dbhelper.openDataBase();
         catch (SQLException e) 
            // TODO Auto-generated catch block
            e.printStackTrace();
        
        //Till here
        GetAll = dbhelper.getAll();
        lv = (ListView) findViewById(R.id.list);
        lv.setAdapter(new ViewAdapter());
    



    public class ViewAdapter extends BaseAdapter 

        LayoutInflater mInflater;

        public ViewAdapter() 
            mInflater = LayoutInflater.from(context);
        

        @Override
        public int getCount() 
            return GetAll.size();
        

        @Override
        public Object getItem(int position) 
            return null;
        

        @Override
        public long getItemId(int position) 
            return position;
        

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

            if (convertView == null) 
                convertView = mInflater.inflate(R.layout.list_item,null);
            

            final TextView names = (TextView) convertView.findViewById(R.id.doctorlist_name);
            final TextView gender = (TextView) convertView.findViewById(R.id.doctorlist_gender);

            names.setText(GetAll.get(position).getname());
            gender.setText(GetAll.get(position).getgender());

            return convertView;
        
    

DatabaseHelper 类

public List<Students> getAll() 

        final int maxCount = 20;

        List<Students> sList = new ArrayList<Students>();
        
            String selectQuery =
                    "SELECT id,full_name,gender FROM students LIMIT " +maxCount+" ";
            Log.e("students query: ", selectQuery);
            SQLiteDatabase db = this.getWritableDatabase();
            Cursor cursor = db.rawQuery(selectQuery, null);

            // looping through all rows and adding to list
            if (cursor.moveToFirst()) 
                do 
                    Students si = new Students();
                    si.setid(Integer.parseInt(cursor.getString(0)));
                    si.setname(cursor.getString(1));
                    si.setgender(cursor.getString(2));

                    sList.add(si);
                 while (cursor.moveToNext());
            
            db.close();
        
        return sList;
    

【参考方案1】：

在下一个按钮单击时将索引增加 20，在上一个按钮单击时将索引减少到 20，您可以通过以下查询实现。

String selectQuery = "SELECT id,full_name,gender FROM students LIMIT 20, "+index;

编辑：

public List<Students> getStudent(int index) 
        final int maxCount = 20;
        List<Students> sList = new ArrayList<Students>();
            String selectQuery = "SELECT id,full_name,gender FROM students LIMIT "+maxCount+", "+index;;
            Log.e("students query: ", selectQuery);
            SQLiteDatabase db = this.getWritableDatabase();
            Cursor cursor = db.rawQuery(selectQuery, null);
            // looping through all rows and adding to list
            if (cursor.moveToFirst()) 
                do 
                    Students si = new Students();
                    si.setid(Integer.parseInt(cursor.getString(0)));
                    si.setname(cursor.getString(1));
                    si.setgender(cursor.getString(2));

                    sList.add(si);
                 while (cursor.moveToNext());
            
            db.close();
        
        return sList;




private int currentPageIndex=0; 
@Override
public void onClick(View view) 
     switch(view.getId())
          case R.id.prevBtn;
                currentPageIndex -=20;
                GetStudent.clear();
                GetStudent.addAll(dbhelper.getStudent(int index));
                adapter.notifyDataSetChanged();
        break;
          case R.id.nextBtn;
                currentPageIndex +=20;
                GetStudent.clear();
                GetStudent.addAll(dbhelper.getStudent(int index));
                adapter.notifyDataSetChanged();
        break;
     

【讨论】：

我将在哪里将其插入到我的 dbhelper 类或我的主要活动中？对不起 android 新手

@GemUbaldo 检查更新的代码。使用 getStudent() 方法检索学生。传递您需要从中获取学生的索引。正如我之前所说，在下一个按钮单击时将索引增加 20，在上一个按钮单击时将索引减少到 20。

我在这一行的主要活动中遇到错误 GetStudent = dbhelper.getStudent(int index);

dbhelper = new DatabaseHelper(MainActivity.this); //在原始代码中添加以下行 try dbhelper.createDataBase(); catch(IOException e) e.printStackTrace(); 尝试 dbhelper.openDataBase(); catch (SQLException e) // TODO 自动生成的 catch 块 e.printStackTrace(); //直到这里 GetStudent = dbhelper.getStudent(int index); lv = (ListView) findViewById(R.id.list); lv.setAdapter(new ViewAdapter());

我替换 GetAll = dbhelper.getAll(); with GetStudent = dbhelper.getStudent(int index);

【参考方案2】：

您可以更改 whereCluse： 例如下一页：（page = 2） id> 20*(page - 1) 和 LIMIT 20*(page)