制作一个APP模拟电子书店的一部分功能。首先需要创建一个名为BookStore.db的数据库，在数据库中新建一张Book表，表中有id(主键)、作者、价格、页数和书名等列。然后增加一些按钮，分别实现对该数据库进行增加或删除书籍，修改价格，查找书籍信息等
操作的功能
在activity_main.xml文件中创建布局，代码如下：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:orientation="vertical"
tools:context="bzu.edu.cn.databasedemo.MainActivity">
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="CreateDatabase"
android:onClick="createDatabase"
android:id="@+id/btnCreateDB"/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="AddDatabase"
android:onClick="addDatabase"
android:layout_marginTop="10dp"
android:id="@+id/btnAddDB"/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="UpdateDatabase"
android:onClick="updateDatabase"
android:layout_marginTop="10dp"
android:id="@+id/btnUpdateDB"/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="DeleteDatabase"
android:onClick="deleteDatabase"
android:layout_marginTop="10dp"
android:id="@+id/btnDeleteDB"/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="QueryDatabase"
android:onClick="queryDatabase"
android:layout_marginTop="10dp"
android:id="@+id/btnQueryDB"/>
</LinearLayout>
新建一个辅助类DBHelper，代码如下：
Android系统推荐使用SQLiteOpenHelper的子类创建SQLite数据库，因此需要创建一个类继承自
SQLiteOpenHelper，重写onCreate（）方法，并在该方法中执行创建数据库的命令。创建数据库的SQL
语句被定义在onCreate（）方法中，当数据库第一次被创建时会自动调用该方法中的SQL语句。当数据库
版本号增加时会调用onUpgrade（）方法，如果版本号不增加，该方法则不会被调用。
package bzu.edu.cn.databasedemo.db;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
import android.widget.Toast;
/**
* Created by Administrator on 2017/4/12.
*/
public class DBHelper extends SQLiteOpenHelper {
private Context context;
public static final String DB_NAME="BookStore.db";
public static final String CREATE_BOOK="create table book(id integer primary key autoincrement,author text,price real,pages integer,name text)";
public static final String CREATE_CATEGORY="create table category(id integer primary key autoincrement,name text,code integer)";
public DBHelper(Context context, int version) {
super(context, DB_NAME, null, version);
Log.d("DBHelper","constructor");
this.context=context;
}
@Override
public void onCreate(SQLiteDatabase db) {
Log.d("DBHelper","onCreate");
db.execSQL(CREATE_BOOK);
db.execSQL(CREATE_CATEGORY);
Toast.makeText(context,"create succeeded",Toast.LENGTH_LONG).show();
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {//数据库的升级
db.execSQL("drop table if exists book");
db.execSQL("drop table if exists category");
onCreate(db);
}
}
package bzu.edu.cn.databasedemo;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;
import bzu.edu.cn.databasedemo.db.DBHelper;
public class MainActivity extends AppCompatActivity {
private DBHelper dbHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dbHelper = new DBHelper(this, 2);
}
public void createDatabase(View v) {//创建建数据库
dbHelper.getWritableDatabase();
}
public void addDatabase(View v) {//添加数据
SQLiteDatabase sqLiteDatabase = dbHelper.getWritableDatabase();
ContentValues contentValues = new ContentValues();
contentValues.put("name", "Java");
contentValues.put("author", "孙卫青");
contentValues.put("pages", 500);
contentValues.put("price", 56.5);
sqLiteDatabase.insert("book", null, contentValues);
contentValues.clear();
contentValues.put("name", "C++");
contentValues.put("author", "Dan");
contentValues.put("pages", 400);
contentValues.put("price", 56);
sqLiteDatabase.insert("book", null, contentValues);
}
public void updateDatabase(View v) {//更新数据
SQLiteDatabase sqLiteDatabase = dbHelper.getWritableDatabase();
ContentValues contentValues = new ContentValues();
contentValues.put("price", 10.8);
sqLiteDatabase.update("book", contentValues, "name=?", new String[]{"Java"});
}
public void deleteDatabase(View v) {//删除数据
SQLiteDatabase sqLiteDatabase = dbHelper.getWritableDatabase();
sqLiteDatabase.delete("book", "pages<?", new String[]{"500"});
}
public void queryDatabase(View v) {//查询数据
StringBuilder stringBuilder = new StringBuilder();
SQLiteDatabase sqLiteDatabase = dbHelper.getReadableDatabase();
Cursor cursor = sqLiteDatabase.query("book", null, null, null, null, null, null);
if (cursor.moveToFirst()) {
do {
//遍历Cursor对象，取出数据并打印
String name = cursor.getString(cursor.getColumnIndex("name"));
String author = cursor.getString(cursor.getColumnIndex("author"));
int pages = cursor.getInt(cursor.getColumnIndex("pages"));
double price = cursor.getDouble(cursor.getColumnIndex("price"));
stringBuilder.append(name + "-" + author + "-" + pages + "-" + price+"\n");
} while (cursor.moveToNext());
}
Toast.makeText(this, stringBuilder.toString(),Toast.LENGTH_LONG).show();
}
}