Android数据存储方式——SQLite数据库的增删改查用法样例和注意事项.txt

声明：
1.sqlite是用的时候才创建
2.oncreate:只执行一次。
*3、执行SQL语句：db.execSQL("update user set username=?, password=? where id=?",new Object[]{user.getUsername(),user.getPassword(),user.getId()});
    注意设置的字段和条件字段之间不能加逗号，否则会报出 near "where": syntax error (code 1): 类型的错误
思路：写一个User工具类，操作User表。
步骤：１.新建User实体类
       2.新建UserServcie工具类：有一个Helper类的属性，在UserServcie的构造函数中实例化Helper类的实例
       3.UserService中写一个addUser(User);
       4.写一个查询所有： 
       public List<User> queryAll() {
        SQLiteDatabase db = helper.getReadableDatabase();
        List<User> list = new ArrayList<>();
        //ResultSet
        Cursor cursor = db.rawQuery("select * from user", null);
        while (cursor.moveToNext()) {
            int id = cursor.getInt(cursor.getColumnIndex("id"));
            String username = cursor.getString(cursor.getColumnIndex("username"));
            String password = cursor.getString(cursor.getColumnIndex("password"));
            User user = new User(id, username, password);
            list.add(user);
        }
        return list;
    }
       5.activity中写页面，实例化控件（两个EditeTest,一个Button,TextView）
       6.点击添加按钮，先插入数据，然后查询所有，展示到Textview上面。

数据处理的类：

package com.work.mysqlite.db;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

import com.work.mysqlite.entity.User;

import java.util.ArrayList;
import java.util.List;

/** * Created by Administrator on 2017/2/28. * 用于操作数据库 */

public class UserService {
    private MySQLHelper helper;

    public UserService(Context context) {
      helper=new MySQLHelper(context);
    }
    //添加数据的方法：
    public void addUser(User user){
        SQLiteDatabase db=helper.getWritableDatabase();
        db.execSQL("insert into user(username,password) values (?,?) ",new Object[]{user.getUsername(),user.getPassword()});
        db.close();
    }
    //查询全部数据的方法：
    public List<User> queryAll(){
        SQLiteDatabase db=helper.getReadableDatabase();
         List<User> list=new ArrayList<>();
        //查询返回结果集用Cursor类接收，表示游标（相当于下标）
        Cursor cursor= db.rawQuery("select * from user",null);
        while (cursor.moveToNext()){//如果有下一个游标，通过数据库中的相应字段获取值
            int id=cursor.getInt(cursor.getColumnIndex("id"));
            String username=cursor.getString(cursor.getColumnIndex("username"));
            String password=cursor.getString(cursor.getColumnIndex("password"));
            User user=new User(id,username,password);
            list.add(user);
        }
        return list;
    }
    //删除数据的方法
    public void delete(String id){
        SQLiteDatabase db=helper.getWritableDatabase();
        db.execSQL("delete from user where id=?",new Object[]{id});
        db.close();
    }
    //修改数据的方法
    public void update(User user){
        SQLiteDatabase db=helper.getWritableDatabase();
        db.execSQL("update user set username=?, password=? where id=?",new Object[]{user.getUsername(),user.getPassword(),user.getId()});
        db.close();
    }
}

自定义adapter

package com.work.mysqlite.adapter;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.EditText;
import android.widget.TextView;

import com.work.mysqlite.R;
import com.work.mysqlite.entity.User;

import java.util.List;

/** * Created by Administrator on 2017/2/28. */

public class UserAdapter extends BaseAdapter {
    private Context context;
    public List<User> list;
    private LayoutInflater inflater;

    public UserAdapter(Context context, List<User> list) {
        this.context = context;
        this.list = list;
        inflater=LayoutInflater.from(context);
    }

    @Override
    public int getCount() {
        return list.size();
    }

    @Override
    public Object getItem(int position) {
        return list.get(position);
    }

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder=null;
       if(convertView==null){
           convertView=inflater.inflate(R.layout.user_item,null);
           holder=new ViewHolder();
           holder.tv_id= (TextView) convertView.findViewById(R.id.tv_id);
           holder.tv_username= (TextView) convertView.findViewById(R.id.tv_username);
           holder.tv_pwd= (TextView) convertView.findViewById(R.id.tv_pwd);
           convertView.setTag(holder);
       }else {
           holder= (ViewHolder) convertView.getTag();
       }
        User user= (User) getItem(position);//获取对应位置的user对象
        holder.tv_id.setText(""+user.getId());
        holder.tv_username.setText(user.getUsername());
        holder.tv_pwd.setText(user.getPassword());
        return convertView;
    }
    class ViewHolder{//声明自定义布局中的变量
        private TextView tv_id,tv_username,tv_pwd;

    }
}

SQLite数据库的创建

package com.work.mysqlite.db;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

/** * Created by Administrator on 2017/2/28. */

public class MySQLHelper extends SQLiteOpenHelper {
    public MySQLHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }
    public MySQLHelper(Context context) {
        super(context, "tset.db", null, 1);
    }


    @Override
    public void onCreate(SQLiteDatabase db) {//本方法只会执行一次，创建一张user表，有一个作为主键自增的int型的id
        String sql="create table user(id integer primary key autoincrement,username varchar(20),password varchar(20))";
        db.execSQL(sql);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }
}

主函数的调用方法

package com.work.mysqlite;

import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.method.ScrollingMovementMethod;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;

import com.work.mysqlite.adapter.UserAdapter;
import com.work.mysqlite.db.MySQLHelper;
import com.work.mysqlite.db.UserService;
import com.work.mysqlite.entity.User;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    private EditText sql_id,sql_username,sql_pwd;
    private Button btn_add,btn_delete,btn_update;
    private ListView sql_lv;
    public List<User> list =new ArrayList<>();
    private UserService service;
    public UserAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        intiView();
    }
    private void intiView(){
        service=new UserService(this);
        sql_id= (EditText) findViewById(R.id.sql_id);
        sql_username= (EditText) findViewById(R.id.sql_username);
        sql_pwd= (EditText) findViewById(R.id.sql_pwd);
        btn_add= (Button) findViewById(R.id.btn_add);
        btn_delete= (Button) findViewById(R.id.btn_delete);
        btn_update= (Button) findViewById(R.id.btn_update);

        sql_lv= (ListView) findViewById(R.id.sql_lv);
// sql_tv.setMovementMethod(ScrollingMovementMethod.getInstance());//设置TextView滚动显示
        btn_add.setOnClickListener(this);
        btn_delete.setOnClickListener(this);
        btn_update.setOnClickListener(this);

        adapter=new UserAdapter(this,list);
        sql_lv.setAdapter(adapter);//将自定义adapter应用于ListView中
        quaryAll();
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.btn_add :
                addUser();
                break;
            case R.id.btn_delete:
                delete();
                break;
            case R.id.btn_update:
                update();
                break;
        }
    }

    //添加数据
    public void addUser(){
        String username=sql_username.getText().toString();
        String password=sql_pwd.getText().toString();
        User user=new User(username,password);
        service.addUser(user);
        quaryAll();
    }
    //查询全部的方法
    public void quaryAll(){
        adapter.list=service.queryAll();
        adapter.notifyDataSetChanged();//刷新页面

// sql_tv.setText("");
// for (int i = 0; i <list.size() ; i++) {
// User user=list.get(i);
// user.setId(i);
// sql_tv.append("id:"+user.getId()+",username:"+user.getUsername()+",password:"+user.getPassword()+"\n");
// }
    }
//删除数据的方法
    public void delete(){
        String id=sql_id.getText().toString();
        service.delete(id);
        quaryAll();
    }
    //修改数据的方法
    public void update(){
        String id=sql_id.getText().toString();
        String username=sql_username.getText().toString();
        String password=sql_pwd.getText().toString();
        User user=new User(Integer.parseInt(id),username,password);
        service.update(user);
        quaryAll();
    }

}