第十二章：Android数据存储（下）

一、SQLite介绍

提到数据存储问题，数据库是不得不提的。数据库是用来存储关系型数据的不二利器。Android为开发者提供了强大的数据库支持，可以用来轻松地构造基于数据库的应用。Android的数据库应用，依托于当下最流行的开源嵌入式数据库SQLite。在Android中，应用的数据库文件是该应用私有的，存储在应用数据目录下的databases子目录内。从代码结构来看，Android的数据库实现可以分成两个层次，在底层通过C++调用SQLite的接口来执行SQL语句，并通过JNI向上暴露Java可访问的接口。

SQLite可视化工具：SQLite Expert Professional 3；

二、Android访问SQLite

主要步骤：

(1)创建某个类继承SQLiteOpenHelper,并重写

-- 带Context参数的构造函数; //用来创建数据库

-- onCreate(SQLiteDatabase db); //在创建数据库时调用

-- onUpgrade(SQLiteDatabase db,int old,int newversion);  //数据库版本更改时调用

(2)创建数据库：SQLiteDatabase db = helper.getWritableDatabase();

(3)SQL语句：db.execSQL(String sql);

 

语句使用：

1.打开数据库

 

SQLiteDatabase db = helper.getWritableDatabase();

SQLiteDatabase db = helper.getReadableDatabase(); //此函数内部其实也调用了getWritableDatabase()函数，即调用了此函数，也可以写数据

 

2.insert语句

 

(1)db.execSQL("insert into person(name,age) values(?,?)",new Object[]{"xiazdong",20});

(2)

ContentValues values = new ContentValues();
values.put("name","xiazdong");
values.put("age",20);
db.insert("tablename",null,values);

3.delete语句

 

(1)db.execSQL("delete from person where id=?",new Object[]{id});

(2)db.delete("tablename","id=?",new String[]{id+""});

 

4.update语句

 

(1)

db.exeSQL("update person set age=? where name=?",new Object[]{30,"xiazdong"});

(2)

ContentValues values = new ContentValues();
values.put("age",30);/*set子句*/
db.update("tablename",values,"name=?"/*where子句*/,new String[]{"xiazdong"}/*where子句参数*/);

5.query语句

 

(1)

Cursor cursor = db.rawQuery("select * from person where name=?",new Object[]{"xiazdong"});
while(cursor.moveToNext()){
    //int index = cursor.getColumnIndex(String name);//根据name获得索引
    //String name = cursor.getString(int index);    //根据索引获得值
    String name = cursor.getString(cursor.getColumnIndex("name"));
}

(2)

Cursor cursor = db.query("tablename",null/*表示select * */,"name=?"/*where语句*/,new String[]{"xiazdong"},null/*group by 语句*/,null/*having 语句*/,null/*order by语句*/,null/*limit 语句*/);

 

6.分页语句

 

Cursor cursor = db.rawQuery("select * from person limit ?,?",new Object[]{5,5});    //第一个5表示跳过5条记录，下一个5为查询结果的记录个数

while(cursor.moveToNext()){

    String name = cursor.getString(cursor.getColumnIndex("name")); 

}

7.获得记录个数语句

 

(1)

Cursor cursor = db.rawQuery("select count(*) from person", null);
cursor.moveToFirst();
int count = cursor.getInt(0);

 

(2)

db.query("person",new String[]{"count(*)"},null,null,null,null,null,null);

 

 

 

 示例代码：

MySQLiteOpenHelper.java:

package com.example.helloandroid;

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

public class MySQLiteOpenHelper extends SQLiteOpenHelper {

    public MySQLiteOpenHelper(Context context, String name,
            CursorFactory factory, int version) {
        super(context, name, factory, version);
        // TODO Auto-generated constructor stub
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub

    }

}

DataBaseActivity.java

package com.example.helloandroid;

import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;

public class DataBaseActivity extends Activity {
      private Button createDatabase, createTable, selectData, insertData,
      updateData, deleteDaata;
      private MySQLiteOpenHelper helper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_data_base);

        // 初始化按钮
        createDatabase = (Button) findViewById(R.id.createDatabase);
        createTable = (Button) findViewById(R.id.createTable);
        selectData = (Button) findViewById(R.id.selectData);
        insertData = (Button) findViewById(R.id.insertData);
        updateData = (Button) findViewById(R.id.updateData);
        deleteDaata = (Button) findViewById(R.id.deleteDaata);

        helper = new MySQLiteOpenHelper(DataBaseActivity.this, "mydb.db",
                null, 1);

        /*
         * 创建数据库
         */
        createDatabase.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                SQLiteDatabase sqlitedatabase = helper.getWritableDatabase();
                Toast.makeText(DataBaseActivity.this, "数据库创建成功", 1000).show();

            }

        });

        /*
         * 创建表
         */
        createTable.setOnClickListener(new OnClickListener() {

            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                SQLiteDatabase sqlitedatabase = helper.getWritableDatabase();
                // 创建表
                sqlitedatabase
                        .execSQL("create table student(id INTEGER PRIMARY KEY autoincrement,name text)");
                Toast.makeText(DataBaseActivity.this, "表创建成功", 1000).show();
            }
        });

        /*
         * 插入数据
         */

        insertData.setOnClickListener(new OnClickListener() {

            public void onClick(View v) {
                // TODO Auto-generated method stub
                SQLiteDatabase sqlitedatabase = helper.getWritableDatabase();
                sqlitedatabase
                        .execSQL("insert into student(name) values ('tinyphp')");
                Toast.makeText(DataBaseActivity.this, "插入数据成功", 1000).show();
            }
        });

        /*
         * 更新数据
         */
        updateData.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                SQLiteDatabase sqlitedatabase = helper.getWritableDatabase();
                sqlitedatabase
                        .execSQL("update student set name='monkey' where id='1'");
                Toast.makeText(DataBaseActivity.this, "数据更新成功", 1000).show();
            }
        });

        /*
         * 查询数据
         */

        selectData.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                SQLiteDatabase sqlitedatabase = helper.getReadableDatabase();

                //参数：表名、查询的列、查询条件、查询参数、查询结果分组、分组结果限制、排序
                Cursor cursor = sqlitedatabase.query("student", new String[] {
                        "id", "name" }, "id=?", new String[] { "1" }, null,
                        null, null);
                String name=null;
                while(cursor.moveToNext()){
                    name =cursor.getString(cursor.getColumnIndex("name"));
                }
                Toast.makeText(DataBaseActivity.this, "查询结果name为："+name, 1000).show();
            }
        });

        /*
         * 删除数据
         * */

        deleteDaata.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                SQLiteDatabase sqlitedatabase =helper.getWritableDatabase();
                sqlitedatabase.delete("student", "id=?", new String[]{"1"});
                Toast.makeText(DataBaseActivity.this, "数据删除成功", 1000).show();
            }
        });

    }
}

activity_data_base.xml

<?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="vertical" >

     <Button
        android:id="@+id/createDatabase"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="创建数据库" />

     <Button
        android:id="@+id/createTable"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="创建表" />

       <Button
        android:id="@+id/insertData"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="插入" />

       <Button
        android:id="@+id/updateData"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="更新" />

       <Button
           android:id="@+id/selectData"
           android:layout_width="match_parent"
           android:layout_height="wrap_content"
           android:text="查询" />

        <Button
        android:id="@+id/deleteDaata"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="删除" />
</LinearLayout>

效果图：