Android使用SQLite保存数据

要使用SQLite首先要建表，建表要继承SQLiteOpenHelper,如下:

package com.example.sqlitedemo4;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;public class MySQLiteOpenHelper extends SQLiteOpenHelper {    private static MySQLiteOpenHelper historySQLiteOpenHelper;    private static String DATABASE_NAME = "school";    /**     * 数据库的构造方法     * 数据库查询的结果集，为null则使用默认的结果集     * 数据库的版本，从1开始，小于1则抛异常     * @param context     */    public MySQLiteOpenHelper(Context context) {        super(context, DATABASE_NAME, null, 1);    }    public static synchronized MySQLiteOpenHelper getSQLiteOpenHelper(Context context){        if (historySQLiteOpenHelper == null){            historySQLiteOpenHelper = new MySQLiteOpenHelper(context.getApplicationContext());        }        return historySQLiteOpenHelper;    }    /**     * 数据库在第一次被创建时调用，表结构，初始化     * @param db 数据库     */    @Override    public void onCreate(SQLiteDatabase db) {        db.execSQL("create table class(id integer primary key autoincrement,name text,age integer,school text)");    }    @Override    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {}}

上面是一个建表的类，在activity中调用,getSQLiteOpenHelper是为了MySQLiteOpenHelper 使用单例模式；activity的布局就一个ListView，activity的代码如下：

package com.example.sqlitedemo4;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import android.os.Bundle;import android.support.v7.app.AppCompatActivity;import android.widget.ListView;import java.util.ArrayList;import java.util.HashMap;import java.util.Map;public class MainActivity extends AppCompatActivity {    private MySQLiteOpenHelper msql;    private SQLiteDatabase db;    private ListView lv;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        lv = (ListView) findViewById(R.id.lv);        msql = MySQLiteOpenHelper.getSQLiteOpenHelper(this);        insertSql();        selectSql();    }    public void insertSql() {        db = msql.getWritableDatabase();        db.execSQL("insert into class values(null,'时崎狂三',23,'A')");        db.execSQL("insert into class values(null,'saber',23,'A')");        db.execSQL("insert into class values(null,'苏九儿',3000,'A')");        db.execSQL("insert into class values(null,'龙三元',2000,'A')");        db.execSQL("insert into class values(null,'郭双',23,'A')");        db.close();    }    public void selectSql() {        db = msql.getWritableDatabase();        ArrayList<Map<String, Object>> list = new ArrayList<>();        String sql = "select * from class";        //String sql = "select * from class order by Id desc";//倒序查找        Cursor cursor = db.rawQuery(sql, null);        cursor.moveToFirst();        while (!cursor.isAfterLast()) {            String name = cursor.getString(cursor.getColumnIndex("name"));            int age = cursor.getInt(cursor.getColumnIndex("age"));            String school = cursor.getString(cursor.getColumnIndex("school"));            Map<String, Object> map = new HashMap<>();            map.put("name", name);            map.put("age", age);            map.put("school", school);            list.add(map);            cursor.moveToNext();        }        MyAdapter adapter = new MyAdapter(this, list);        lv.setAdapter(adapter);    }    @Override    protected void onDestroy() {        super.onDestroy();        db.execSQL("DELETE FROM class");//清空表数据        db.close();    }}

如代码所示，如果要使用倒序查找就使用sql语句String sql = "select * from class order by Id desc";；
如果要顺序查找就使用String sql = "select * from class";，在最后需要关闭SQLiteDatabase；
db.execSQL("DELETE FROM class");是清空表数据，而并非删除表
最后在附上adapter的代码：
布局 ：

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="horizontal">    <TextView        android:id="@+id/tv_name"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_marginLeft="10dp"        android:layout_marginTop="10dp" />    <TextView        android:id="@+id/tv_age"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_marginLeft="10dp"        android:layout_marginTop="10dp" />    <TextView        android:id="@+id/tv_school"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_marginLeft="10dp"        android:layout_marginTop="10dp" /></LinearLayout>

代码

package com.example.sqlitedemo4;import android.content.Context;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.TextView;import java.util.List;import java.util.Map;public class MyAdapter extends BaseAdapter {    private List<Map<String, Object>> list;    private Context context;    public MyAdapter(Context context,List<Map<String, Object>> list) {        this.context = context;        this.list = list;    }    @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 vh = null;        if(convertView == null){            convertView = LayoutInflater.from(context).inflate(R.layout.item_main, null);            vh = new ViewHolder();            vh.tv_name = (TextView) convertView.findViewById(R.id.tv_name);            vh.tv_age = (TextView) convertView.findViewById(R.id.tv_age);            vh.tv_school = (TextView) convertView.findViewById(R.id.tv_school);            convertView.setTag(vh);        }else{            vh = (ViewHolder) convertView.getTag();        }        vh.tv_name.setText(list.get(position).get("name").toString());        vh.tv_age.setText(list.get(position).get("age").toString()+"");        vh.tv_school.setText(list.get(position).get("school").toString());        return convertView;    }    public class ViewHolder{        public TextView tv_name;        public TextView tv_age;        public TextView tv_school;    }}

效果图: